from feed to milk

7/31/2019 From Feed to Milk

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FROM FEEDTO MILK:UNDERSTANDING

RUMEN FUNCTION

EXTENSION CIRCULAR 422


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CONTENTS

Part I: Background in Basic Nutrition of Dairy Cattle .. .. .. .. .. .. .. .. .. .. .. .. .. . 1Rumen physiology ................................................................................................................ 1

Rumination and saliva production ..................................................................................... 3

Function of the rumen........................................................................................................... 3

Rumen microbiology ............................................................................................................. 4

Microbial digestion in the rumen ........................................................................................ 6

Carbohydrates ................................................................................................................ 6

Protein ............................................................................................................................. 8

Lipids ............................................................................................................................... 8

Vitamins .......................................................................................................................... 8

Basic nutritional concepts behind feeding dairy cattle .................................................... 8

Dry matter intake and its effect on the cow ..................................................................... 11

Part II: Feed and Feed Nutrients for Dairy Cattle .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 13

Carbohydrates ...................................................................................................................... 13

Fats ......................................................................................................................................... 15

Protein ................................................................................................................................... 17

Energy ................................................................................................................................... 21Minerals ................................................................................................................................ 23

Vitamins ................................................................................................................................ 25

Water ...................................................................................................................................... 26

List of FiguresFigure 1. Summary of digestion and absorption in the ruminant. ............................................ 2

Figure 2. Ruminal fermentation as a consequence of adaptation due to pH regulation. .......... 6

Figure 3. Feed, nutrient flow from the rumen, and milk components. ..................................... 6

List of Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inside back cover

Prepared by Virginia Ishler, extension assistant in the Department of Dairy and Animal

Science; Jud Heinrichs, professor of dairy and animal science; and Gabriella Varga, associate

professor of animal science.

Development of this publication was made possible through a grant from Church & Dwight Co.,

Inc., manufacturers of ARM & HAMMER feed ingredients.


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TABLESTable 1. Rate of passage of feed for dry cows and lactating cows. ................................ 1

Table 2. Effect of ration on eating rate and on saliva production. ................................. 3

Table 3. Chemical composition of saliva from cattle. ....................................................... 3Table 4. Typcial composition of rumen gases.................................................................... 4

Table 5. Grouping of rumen bacterial species according to the typeof substrates fermented. ........................................................................................ 5

Table 6. Effect of forage to concentrate ratio on the volatile fatty acidproportions in the lactating cow. .......................................................................... 7

Table 7. Estimated rumen fermentation characteristics. .................................................. 7

Table 8. Feed ingredient sources that are utilized by ruminants. .................................. 8

Table 9. Eating, rumination behavior, rumen pH, volatile fatty acids (VFAs),average milk yield, and milk composition as influenced by particlesize of the ration. ..................................................................................................... 9

Table 10. Differences in extent of ruminal digestion of starches as affectedby source and processing. ................................................................................... 10

Table 11. Target scores for stages of lactation using the 5-pointbody condition scale. ............................................................................................ 11

Table 12. Classification of concentrate ingredients. ......................................................... 13

Table 13. Carbohydrate fractions for some common forages andfeed ingredients. ................................................................................................... 14

Table 14. Fiber partition in various forages. ...................................................................... 15

Table 15. Guidelines for forage neutral detergent fiber (NDF) andforage dry matter intakes. ................................................................................... 15

Table 16. Guide to carbohydrate composition in rations forhigh-producing dairy cows. ................................................................................ 15

Table 17. Fatty acid profile of various commodity and specialty fat sources............... 16

Table 18. Crude protein and protein fractions in various forages andfeed ingredients. ................................................................................................... 17

Table 19. Average distribution of protein and nitrogen fractions insome feedstuffs. .................................................................................................... 18

Table 20. List of the essential and nonessential amino acids. ......................................... 19

Table 21. The essential amino acid profiles of milk, ruminal bacteria, and feeds. ...... 19

Table 22. Guide to protein composition in rations for high-producingdairy cows. ............................................................................................................. 20

Table 23. Regression equations for estimating energy values of various feeds. .......... 20

Table 24. Calculation of cattle NEM and NEG values. .................................................... 21

Table 25. Summarization of minerals in the dairy ration. ............................................... 22

Table 26. Guide to mineral composition in rations for high-producing cows. ............ 24

Table 27. Summarization of fat-soluble vitamins in the dairy ration. ........................... 25

Table 28. Guide to vitamin composition in rations for high-producingdairy cows. ............................................................................................................. 25

Table 29. Water intake needs by various age groups of dairy cattle,drinking water only. ............................................................................................. 26

Table 30. Interpretation of a water analysis report. .......................................................... 27


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PART I: BACKGROUNDIN BASIC NUTRITIONOF DAIRY CATTLE

Feed costs represent 45 to 60 percent ofthe total cost of producing milk.The key to maximizing dairy farmprofitability is to maintain nutrient levelswhile carefully managing feed costs.When optimal nutrition is achieved, cowswill produce better quality and largerquantities of milk. Overall health shouldimprove, resulting in cost savings inveterinary fees, breeding, and treatmentwith drugs.

A basic understanding of animal

nutrition as it applies to dairy cattle isessential to good herd management.Proper feeding of the dairy cow iscomplicated and requires a combinationof scientific knowledge, creativity, andgood management skills to balance theneeds of the rumen microorganisms andthe needs of the animal.

Rumen physiologyWhat makes ruminant animals unique istheir four stomach compartments: thereticulum, the rumen, the omasum, andthe abomasum. The reticulum and therumen are often discussed together

because they are adjoining compart-ments. The reticulum is actually thelargest of the various sacs of the rumen.Digestion of feedstuffs by microorgan-isms takes place in both stomachcompartments.

The reticulum, often called theblind pouch, is the first stomach

compartment. If the cow consumes metalor other large indigestible items, thehoneycomb structure of the stomach wallacts as a sieve and prohibits any hard-ware from moving further into thedigestive tract. Feed that enters thereticulum is later regurgitated andremasticated as part of the cud. Thereticulum can contain up to 2.5 gallons ofundigested feed and feed being digested(digesta).

The rumen is a large, hollow

muscular organ. The rumen developsanatomically in size, structure, andmicrobial activity as the calfs diet ischanged from liquid milk or replacer todry feed or silages. In the matureruminant, the rumen nearly fills theentire left side of the abdominal cavity.

The rumen is a fermentation vat thatcan hold 40 to 60 gallons of material andis the site of microbial activity. Anestimated 150 billion microorganisms perteaspoon are present in its contents. They

consist of bacteria, protozoa, and fungi.Bacteria require a warm, moist, oxygen-free environment for optimum growth.This type of environment is naturallymaintained in the rumen with a tempera-ture range of 100 to 108oF. If cows are feda proper balance of forages and grain, thepH should range between 5.8 and 6.4,which allows the growth of many speciesof bacteria.

The omasum is sometimes referredto as the manyplies because of its

many layers of muscular tissue. In theomasum, the particle size of digesta isreduced, and any excess water isremoved before the digesta enters theabomasum. The omasum can contain upto 4 gallons of digesta.

The fourth compartment is theabomasum or true stomach, whereacids and enzymes further digest thecows digesta. It is the first true glandularportion of the gastrointestinal tract wherethe stomach walls secrete enzymes. Itfunctions very similarly to the stomach ofmany simple stomached animals such asthe pig. This stomach compartment canhold approximately 5 gallons of material.The time that digesta remains in theabomasum is very short compared to theretention time of feeds in the rumen. Theturnover rate of feedstuffs in the rumenand total retention time in the digestivetract, for lactating and dry cows, areshown in Table 1.

The presence of food in the aboma-sum stimulates hydrochloric acidproduction. Hydrochloric acid convertspepsinogen to pepsin, which breaksdown protein to shorter molecular chaincompounds such as peptides and aminoacids for further digestion and absorp-tion in the small intestine. The truestomach has a low pH of 2 to 4, duelargely to this acid production. Some fatdigestion also occurs in the true stomach.

Digesta flowing from the abomasum

to the small intestines is composed ofsmall particles suspended in liquiddigesta. There is little sorting of particu-late matter, and the flow of liquid andparticles is rather similar. As digestapasses through the small intestine, thepH increases at a relatively slow rate.This has important implications forenzymatic activity in the intestine

because enzymes secreted by thepancreas and intestinal mucosa generallyhave a pH optimum which is neutral to

slightly alkaline.

Table 1. Rate of passage of feed for dry cowsand lactat ing cows.

ITEM DRYCOWSa MILKCOWSa

Body weight, lb 1541 1381

Dry matter intake, lb/day 23.8 43.5

Milk production, lb/day 53.6

Ruminal mean retention

time, hr

Grain 25.6 19.4

Hay 30.0 30.3Total mean retention time

in the digestive tract, hr

Grain 47.0 39.2

Hay 55.3 50.7

Source: Adapted from Hartnell, G. F. and L. D.

Satter. 1979. Determination of rumen fill,

retention time and ruminal turnover rates of

ingesta at different stages of lactation in dairy

cows. J. Anim. Sci. 48:381.

aMeans reported in this table were taken from

four dry cows and four lactating cows.


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B B B B

Amino acids Fatty acids Glucose

and

Glycerol

Peptides

Starches

Peptides Fats Sugars

Nonprotein nitrogen(NPN) Feed proteins Fats Carbohydrates

NPN Feed proteins Fats Cellulose Starches

Hemicellulose Sugars

Bacterial Feed

protein protein

Bacterial protein Glucose

(contains essential Volatile fatty acids

amino acids) (VFA's)

VFA's

B

BB

Bile salts, which are synthesized inthe liver from cholesterol, aid in main-taining this alkaline pH in the smallintestine. They also act as emulsifiers that

separate fat globules and give lipaseenzymes more surface area upon whichto act. Both the biliary and the pancreaticsecretions neutralize the gastric acids andprovide enzymes for hydrolysis ofstarches, proteins, and lipids. The smallintestine is the main absorption site forthese breakdown products (Figure 1).

In adult ruminants fed high foragediets, virtually all of the soluble sugars aswell as most of the starch in feeds arefermented by the rumen microbial

population. However, animals fed highgrain diets at high intake levels may haveas much as 50 percent of the dietarystarch escape ruminal fermentation and

be presented in the lower tract fordigestion. In these circumstances,substantial amounts of glucose may beabsorbed from the small intestine.

Protein reaching the small intestineof the ruminant is derived from threesources: (a) dietary protein that hasescaped breakdown by rumen microbes;

(b) protein contained in bacterial andprotozoal cells that flow out of therumen; and (c) endogenous proteinscontained in sloughed cells and secre-tions into the abomasum and intestine.Pancreatic and intestinal proteases breakdown these forms of protein so the aminoacids and peptides can be absorbed in thesmall intestine.

Figure 1. Summary of digestion and absorption in the ruminant.

2 FROM FEEDTO MILK: UNDERSTANDING RUMEN FUNCTION

DIGESTIVEORGAN FEEDCONSTITUENT

KEY: = some absorbed = main site of absorption B = bacterial action

MOUTH

RETICULUM

RUMEN

OMASUM

ABOMASUMORTRUESTOMACH

SMALLINTESTINE


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Lipids arriving in the small intestineare primarily esterified fatty acids andphospholipids. Triglycerides that escaperuminal breakdown and esterified fatty

acids of microbial origin are readilyhydrolyzed by pancreatic lipase torelease free fatty acids. These areabsorbed by the intestinal mucosal cells.

Any material that has not beenutilized in the digestive tract to this pointenters the large intestine. Absorption ofwater, minerals, nitrogen, and volatilefatty acids occurs in the large intestine.The homostatic functions of the largeintestine involve electrolyte balance,some microbial fermentation, and

temporary storage for excreta. Anyproducts that have not been digested willpass out through the feces. Fecal materialcontains undigested feed, metabolic fecalnitrogen, and undigested fat and

bacteria.

Rumination and saliva productionA ruminant animal has the ability toingest feed rapidly and to complete thechewing at a later time. This process isknown as rumination. The steps involved

are regurgitation of the feed, remasti-cation or rechewing, resalivation, andreswallowing of rumen digesta. Theprocess of rumination reduces theparticle size of feeds, which enhancesmicrobial function and allows foreasier passage out of the stomachcompartments.

The regurgitated material is called abolus or cud and consists primarilyof chewed material coated with saliva.Saliva is a major secretion into thedigestive tract, and its production isdirectly related to the amount of time acow spends eating and ruminating(Table2). Production of saliva in amature ruminant can exceed 47.5 gallonsper day when cows chew six to eighthours per day.

Saliva is rich in mineral ions,particularly sodium, phosphate, and

bicarbonate, which serve as bufferingagents in the digestive system (Table 3).

Saliva neutralizes the acids producedduring fermentation and helps tomaintain an ideal environment for

bacteria growth.

Production of saliva can be encour-aged by controlling the ruminants diet.The more a cow chews, the more saliva itproduces. The amount of time a cowspends chewing is influenced by feedingmanagement practices and the nature ofthe diet. The order in which feed ingredi-ents are fed, the particle size of the feeds,the number of times during the day cowsare fed, and the type of feed consumedcan all directly affect saliva production.Long hay stimulates the greatest amount

of chewing, rumination, and salivaproduction. Feeding forages high in cellwall content or neutral detergent fiberwould tend to increase rumination time.

Rumination may be significantlyreduced, for example, by feeding highamounts of concentrates and finelychopped forages. High moisture feeds

such as pasture or silage can reducesaliva produced per pound of dry matterintake by 50 percent. Grains or pelletedfeeds can reduce the flow to 20 percent ofthat on a long-hay diet. Saliva productioncan drop dramatically if the cow does notreceive adequate effective fiber, which isdefined as a combination of forageparticle size and forage neutral detergentfiber intake.

Function of the rumen

The rumen through its strong muscula-ture allows mixing and churning ofdigesta. The movement of the rumenmixes the contents, promoting turnoverand accessibility of the coarser forageparticles for regurgitation, cud chewing,size reduction, and microbial digestion.Fine forage particles, dense concentrateparticles, and materials which have

become hydrated tend to congregate nearthe bottom. Particles tend to move outfrom the rumen as they are reduced in

size through cud chewing and microbialaction. The microbes also pass from therumen for possible digestion in the lowergastrointestinal tract.

The structuring and composition ofrumen contents is influenced by diet.Since the dairy cow consumes such avaried selection of feedstuffs and feedparticle sizes, rumen contents do nothave a uniform composition, and as aresult there is stratification of feedparticles. Long-hay diets producecontents with a large, less dense, floatinglayer beneath the gas dome with rela-tively liquid contents and suspendedfiber beneath. Denser material sinks tothe bottom of the rumen. The floatingmat is composed of the more recentlyingested forage. In diets where forageparticle size is fine and forage neutraldetergent fiber is low, the floating mat isdiminished, but this occurs to a muchgreater extent when high levels of

PART I: BACKGROUNDIN BASIC NUTRITIONOF DAIRY CATTLE 3

Table 2. Effect of rat ion on eating rate and onsaliva production.

EATINGRATE SALIVARYPRODUCTIONPOUNDSOF TEASPOONS/POUND

FEED FEED/MIN OFFEED

Pelleted .79 1.0

Fresh grass .62 1.5Silage .55 2.0

Dried grass .18 5.0

Hay .15 6.0

Source: Bailey, C. B.1958. The role of secretion of

mixed saliva in the cow. In: Proceedings of the

Nutrition Society, p. xiii.

Table 3. Chemical composition of saliva fromcattle.

ELEMENT mEq/la

Sodium 126

Potassium 6

Phosphate 26

Chloride 7

Bicarbonate 126

Source: Bailey, C. B. and C. C. Balch. 1961. Saliva

secretion and its relation to feeding in cattle.

British Journal of Nutrition 15:371.

amEq/l is milliequivalents per liter.


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pelleted grain or concentrates are fed.The rumen contents with these types ofdiets are generally more viscous.

The function of the rumen as a

fermentation vat and the presence ofcertain bacteria promote the develop-ment of gases. These gases are found inthe upper part of the rumen with carbondioxide and methane making up thelargest portion (Table4). The proportionof these gases is dependent on rumenecology and fermentation balance.Ordinarily, the proportion of carbondioxide is two to three times that ofmethane, although a large quantity ofcarbon dioxide is reduced to methane.

Approximately 132 to 264 gallons of gasproduced by fermentation are belchedeach day. The eructation of gases via

belching is important in bloat prevention.

period of two to three weeks is usuallyneeded.

The development of the ruminalpapillae is related to the production of

certain acids from the fermentation offeeds. Increasing the proportions ofbutyric and propionic acids, as seen withhigh grain rations, increases blood flowto the ruminal epithelium, whichstimulates vascular budding andepithelial cell proliferation. Papillaeeither grow in size and number orshorten in size, depending on the dietand the fermentation acids produced.

Rumen microbiology

The objective of feeding dairy cattlenutritionally balanced diets is to providea rumen environment that maximizesmicrobial production and growth. Whendesigning rations for ruminants, theneeds of both the animal and the rumenmicroorganisms must be considered. Inorder to optimize animal performance,compromises in feeding the microbes orthe cow may occur.

The microbial population in therumen consists of bacteria, protozoa, and

fungi. The majority of the concentrationis as bacteria, which can number 1010 to1011 cells/gram of rumen contents.Bacteria can be grouped according totheir three main shapes (cocci, rods, andspirilla), according to their size (generallyfrom 0.3 to 50 m), and according to theirdifferent structures. They can also begrouped according to the type ofsubstrate fermented and are categorizedinto eight distinct groups of rumen

bacteria (Table 5). These species ofbacteria degrade or utilize products suchas cellulose, hemicellulose, starch, sugars,intermediate acids, protein, and lipidsand produce methane. An expandedclassification could include pectinutilizers and ammonia producers. Mostspecies of bacteria are capable of ferment-ing more than one substrate.

The methane-producing bacteria area special class of microorganisms

responsible for regulating the overallfermentation in the rumen. They removehydrogen gas by reducing carbon dioxidewith hydrogen gas to form methane.

Producing methane keeps the hydrogenconcentration in the rumen low, whichallows methanogenic bacteria to promotethe growth of other bacterial species andprovides for a more efficient fermenta-tion. The effective removal of hydrogen

by these methanogenic species encour-ages hydrogen-producing species toproduce more hydrogen and thus altertheir metabolism towards higher yieldingpathways. These higher yieldingpathways result in the synthesis of more

microbial cells, which increases availableprotein to the ruminant.

The protozoa in the rumen numberabout 105 to 106 cells/gram of rumencontents and are influenced by feedingpractices. Higher numbers of protozoaare generally found in the rumen whendiets of high digestibility are fed.Different types of diets seem to encour-age different protozoal genera. Someprotozoa numbers are higher when dietscontain large amounts of soluble sugars

and other types predominate with highstarch diets.

The protozoa actively ingest bacteriaas a source of protein. They also appearto be a stabilizing factor for fermentationend products. Protozoa, like bacteria andfungi, contribute to fiber digestion. Whilethe protozoa are an integral part of themicrobial population and have a markedeffect on the fermentation, their benefit tothe ruminant is still controversial.

The anaerobic fungi are the most

recently recognized group of rumenmicrobes. When animals are fed a highforage diet, rumen fungi may contributeup to 8 percent of the microbial mass.While it is still unclear whether thesefungi are functionally significant, theyhave been shown to degrade celluloseand xylans, indicating some role in fiberdigestion.


The mucosal surface of the rumen ischaracterized by ruminal papillae, theorgans of absorption. Papillae distribution,size, and number are closely related toforage to concentrate ratio, feeding habits,forage availability, and digestibility.

If a ruminants diet is significantlyaltered, as in moving from a high foragediet to a high grain diet or a dry cowration to a lactating cow diet, this changeshould be implemented gradually toallow ruminal papillae time to adapt tonutritional changes. An adaptation

Table 4. Typical composition of rumen gases.

COMPONENT AVERAGEPERCENT

Hydrogen 0.2

Oxygen 0.5

Nitrogen 7.0

Methane 26.8

Carbon dioxide 65.5

Source: Sniffen, C. J. and H. H. Herdt. The

Veterinary Clinics of North America: Food Animal

Practice, Vol 7, No 2. Philadelphia, Pa.: W. B.

Saunders Company, 1991.


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Consideration of microbial repro-duction rate is essential when makingdietary changes in any ruminant. Majorchanges in the diet require a period of

transition to allow for shifts in thepopulations of different microbialspecies. This adaptation may take severaldays. One of the most common problemsencountered in nutrition management issudden changes in the ruminants diet toinclude large amounts of readily ferment-able carbohydrates. Feeding diets of thistype results in a succession of changes inthe rumen microbial population duringthe adaptation period, specifically inthose bacteria which produce and

utilize lactate.In this type of scenario, the acid-

sensitive lactate utilizers are replaced byacid-tolerant lactate utilizers. Lacticacidosis arises from this abrupt shift to ahigh concentrate diet and keeps theeffective lactate-utilizing species fromincreasing in sufficient numbers toprevent the accumulation of lactate. Thisresults in decreasing the rumen pH to avery acidic level, less than 5.5.

Rumen pH is one of the most

variable factors which can influence themicrobial population and the levels ofvolatile fatty acids produced (Figure 2).The rumen pH at which certain functionsare optimized can differ. There are two

basic groups of bacteria which function atvarious pHs. The fiber digesters are mostactive at a pH of 6.2 to 6.8. Cellulolytic

bacteria and methanogenic bacteria canbe reduced when the pH begins to fallbelow 6.0. The starch digesters prefer amore acidic environment, a pH of 5.2 to

6.0. Certain species of protozoa can begreatly depressed with a pH under 5.5. Toaccommodate all these needs, normalfeeding practices should maintain a pHrange between 5.8 to 6.4.


Table 5. Grouping of rumen bacterial species according to the type of substrates fermented.

There are three interconnectingenvironments in which the microbes arelocated in the rumen. The first is the liquid

phase, where free-living microbial groupsin the rumen fluid feed on solublecarbohydrates and protein. This portionmakes up 25 percent of the microbialmass. Next is the solid phase, where themicrobial groups associated with orattached to food particles digest insolublepolysaccharides, such as starch and fiber,as well as the less soluble proteins. Thiscan make up as much as 70 percent of themicrobial mass. In the last phase, 5percent of the microbes attach to therumen epithelium cells or to the protozoa.

Microbial attachment in the rumenhas numerous implications in theruminant. In order for bacteria tomaintain their numbers in the rumen, itis necessary that their reproduction time

be shorter than the turnover rate of therumen digesta. Since the passage rate ofthe particulate phase is much slower thanthat of the liquid phase in the rumen,slower-growing species attach to particlematter and are thereby prevented from

being washed out of the rumen. The dietfed to the dairy cow influences thenumber and relative proportions of thedifferent microbial species in the rumen.

Source: Church, D. C., ed. The Ruminant Animal: Digestive Physiology and Nutrition.

Englewood Cliffs, N.J.: Prentice Hall, 1988.

Major Cellulolytic Species

Bacteroides succinogenes

Ruminococcus flavefaciens

Ruminococcus albus

Butyrivibrio fibrisolvens

Major Pectinolytic Species


Bacteroides ruminicola

Lachnospira multiparus

Succinivibrio dextrinosolvens

Treponema bryantii

Streptococcus bovis

Major Ureolytic Species

Succinivibrio dextrinosolvens

Selenomonas sp.

Bacteroides ruminicolaRuminococcus bromii

Butyrivibrio sp.

Treponema sp.

Major Sugar-utilizing Species

Treponema bryantii

Lactobacillus vitulinus

Lactobacillus ruminus

Major Proteolytic Species

Bacteroides amylophilus



Streptococcus bovis

Major Lipid-utili zing Species

Anaerovibrio lipolytica


Treponema bryantii

Eubacterium sp.

Fusocillus sp.

Micrococcus sp.

Major Hemicell ulolytic Species



Ruminococcus sp.

Major Amylolytic Species

Bacteroides amylophilus

Streptococcus bovis

Succinimonas amylolytica


Major Methane-producing Species

Methanobrevibacter ruminantium

Methanobacterium formicicum

Methanomicrobium mobile

Major Acid-utilizing Species

Megasphaera elsdenii

Selenomonas ruminantium

Major Ammonia-producing Species


Megasphera elsdenii

Selenomonas ruminantium


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Figure 2. Ruminal fermentation as a consequence of adaptation due to pH regulation.Microbial digestion in the rumenThe rumen provides a site where therumen microorganisms can digestcarbohydrates, proteins, and fiber.

Through this digestion process, energy orvolatile fatty acids (VFAs) and microbialprotein that can be utilized by the animalare produced (Figure3).

Carbohydrates

When carbohydrates, both structural(neutral detergent fiber) and non-structural (sugars and starches), undergomicrobial fermentation, they produceVFAs. The primary VFAs in descendingorder of abundance are acetic, propionic,

butyric, isobutyric, valeric, isovaleric,and traces of various other acids. TheVFAs can provide up to 80 percent of theenergy needs of the animal.

Acetic acid can constitute 50 to 60percent of the total VFAs. It predomi-nates in a high forage diet. Acetate isused for fatty acid synthesis and is themain precursor for lipogenesis in adiposetissue. Some acetate is also used formuscle metabolism and body fat.Production of adequate levels of acetatein the rumen is essential to maintainadequate quantities of milk fat.

Acetic acid levels can drop if there isa lack of effective fiber in the ration. Thiscan also occur when feeding a heavyconcentrate diet or a diet high in heat-treated starch as in pelleting, steamcrimping, or steam flaking. High intakesof oil can also depress acetic acid.

Propionic acid can make up 18 to 20percent of the total VFAs. It reaches its

highest concentration in a high grain diet.Propionic acid provides energy throughconversion to blood glucose in the liver.It is also used in lactose or milk sugarsynthesis.

Butyric acid provides energy to therumen wall and makes up 12 to 18percent of the total VFAs. It is largelyconverted to ketones during absorptionthrough the rumen epithelium. B-hydro-xybutric acid (B-HBA) accounts for morethan 80 percent of the ketones. B-HBA is


used for fatty acid synthesis in adiposeand mammary gland tissues.

The proportion of VFAs are greatlyinfluenced by diet and the status of themethanogenic population in the rumen.Despite wide swings in the microbialpopulation and differences in feed intake,

ruminal VFA proportions are fairly stableamong diets with varying forage toconcentrate ratios. However, the ruminalproportions of VFAs are largely pHdependent.

In general, as the forage to concen-trate ratio decreases, the acetate to

Mol %

70

60

50

40

30

20

10

7 6 5 Rumen pH

Lacticacid

Propionicacid

Aceticacid

Active Activecellulolytic amylolytic

flora flora

Kaufman, W., H. Hagemeister, and G. Durksen. Adaptation to changes in dietary composition level andfrequency of feeding. In: Digestive Physiology and Metabolism in Ruminants, ed. Y. Ruckebusch and P.

Thivend. Westport, Ct.: AVI Publishing, 1980, p. 587.

Figure 3. Feed, nutrient f low from the rumen, a nd milk components.

Crude Sugar, Fermentable Fatprotein starch fiber

DIP

Microbial growth and fermentation

Microbial protein

Amino Propionic Acetic, Fattyacids (glucose) butyric acids

Milk Milk Milkprotein lactose fat

UIP

Source: Sniffen, C. J. and H. H. Herdt. The Veterinary Clinics of North America: Food Animal Practice,Vol 7, No 2. Philadelphia, Pa.: W. B. Saunders, 1991.

Note: UIP = undegradable intake protein; DIP = degradable intake protein.

FEED

NUTRIENTS

MILKCOMPONENTS


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Table 6. Effect of forage to concentrate rat io on the volatile fa tty acid proportions in thelactating cow.

MOLARRATIOS, %

FORAGETOCONCENTRATERATIO ACETATE PROPIONATE BUTYRATE

100:00 71.4 16.0 7.975:25 68.2 18.1 8.0

50:50 65.3 18.4 10.4

40:60 59.8 25.9 10.2

20:80 53.6 30.6 10.7

Source: Physiology of Digestion and Metabolism in the Ruminant, ed. A.T. Phillipson. Newcastle-upon-

Tyne, England: Oriel Press, 1970, p. 422.

Table 7. Estimated rumen fermentation characte ristics.

PROPORTIONOFCARBOHYDRATECONVERTEDTOb

SUBSTRATE DIETa ACETATE PROPIONATE BUTYRATE

Soluble carbohydratec F 0.69 0.20 0.10

C 0.45 0.21 0.30

Starch F 0.59 0.14 0.20

C 0.40 0.30 0.20

Hemicellulose F 0.57 0.18 0.21

C 0.56 0.26 0.11

Cellulose F 0.66 0.09 0.23

C 0.79 0.06 0.06

Source: Murphy, M. R., R. L. Baldwin, and L. J. Koong. 1982. Estimation of stoichiometric parameters for

rumen fermentation of roughage and concentrate diets. J. Animal Sci. 55:411-421.

aF codes forage diets; C codes diets containing more than 50 percent of a cereal-based concentrate diet.

bRatios do not add up to 100 because the isoacids are not taken into account.

cSoluble carbohydrate fraction includes organic acids and pectin in this analysis.

Note: The acetate to propionate ratio resulting from fermentation of hemicellulose in a high forage diet

was 3.2, but only 2.2 when fermented in a high grain diet. The acetate to propionate ratio from cellulose

fermentation also varied with diet, 13.1 for a forage diet and 7.3 for a grain diet, both being much higher

than that produced by hemicellulose.

propionate ratio also decreases (Table 6).As cellulose and hemicellulose levelsincrease relative to soluble carbohydrateand starch levels, the acetate to propi-

onate ratio also tends to increase.However, VFA production from a givensubstrate such as cellulose or starchvaries with diet composition (Table 7).Although cellulose and hemicellulose areusually digested simultaneously inforages, the end-products produced mayvary depending on diet.

The vast majority of VFAs arepassively absorbed through the rumenwall. This continuous removal of VFA byabsorption from the reticulo-rumen is

important for maintaining a stableruminal pH. Removal of acid products isalso important for the continued growthof cellulolytic organisms. VFAs thatremain in the digesta flow from therumen to the lower tract and are ab-sorbed by the omasum and abomasum.

Rate of VFA absorption from therumen is influenced by the chain lengthof individual acids and ruminal pH.Increasing the chain length of the acidresults in increased absorption rates in

the following order: butyrate greater thanpropionate greater than acetate. LowerpH and the resultant increases in theproportion of the acids in the rumenfavor more rapid absorption.

The net absorption of VFAs reachingthe blood is dependent on the concentra-tion in the rumen and the quantity used

by the rumen wall. The rates of utiliza-tion by the rumen wall are for butyrate propionate acetate. As a result ofthe higher concentration in the rumen

and the low rate of utilization by therumen wall, acetate enters the blood inthe greatest quantity, followed bypropionate. Very little butyrate enters the

blood due to the lesser amount in therumen and greater amount metabolized

by the rumen wall.Lactic acid is important when starch

is a part of the diet and is itself fermentedto acetate, propionate, and butyrate.Lactate, when present, is absorbed


directly through the rumen wall. Lacticacid does not accumulate to any largeextent in dairy cattle that have been fednutritionally sound rations that aremanaged properly. If gradual introduc-tion of grains is practiced, the lactate-utilizing bacteria will develop and permitonly a transient increase in lactic acidaccumulation following ingestion of adiet high in readily fermentable carbohy-

drates. Problems arise when largeamounts of starch or cereal concentratesare fed. Total lactate in severe cases maycomprise 50 to 90 percent of the totalrumen acids. The absorption of largeamounts of lactic acid across the rumenwall to the blood produces systemicacidosis and results in animals goingoff feed, developing laminitis, andperforming poorly overall.


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Protein

Another critical function of the rumenmicrobes is synthesis of microbialprotein. The biological value of microbial

protein is 66 to 87 percent. Dietaryprotein may be improved or reduced inbiological value by rumen microbes,depending on the quality of protein fed.

Most ruminal bacteria can useammonia nitrogen as a source of nitro-gen. Some species of bacteria requireadditional nitrogen compounds such asintact protein or carbon chains of certainamino acids for most efficient or rapidgrowth.

Ammonia is derived in the rumen

through microbial degradation of dietaryprotein and dietary nonprotein nitrogen,from hydrolysis of recycled urea to therumen, and from degradation of micro-

bial crude protein. Rumen ammoniadisappears from the rumen in differentways, such as incorporation of thenitrogen by the microbes, absorptionthrough the rumen wall, and flushing tothe omasum.

Ammonia not taken up by themicrobes is absorbed directly through the

rumen wall. The rate of absorption isdependent on the pH of the rumenenvironment and the concentration ofammonia. Absorption is rapid at a pH of6.5 or higher. It declines to nearly zero ata pH of 4.5. Ammonia absorptionincreases as ruminal concentrationincreases. Indications of ammoniatoxicity include ruminal ammoniaconcentration above 100 mg/dl, ruminalpH above 8, and blood plasma ammoniaconcentrations above 2 mg/dl.

Substitution of dietary nonproteinnitrogen, such as urea, for protein fromplant and animal sources can reducecosts of protein supplementation. Urea isdegraded by the microbes into ammonia,which can be used for microbial synthesisresulting in microbial protein. Themicrobes can also utilize nonproteinnitrogen in ensiled feeds and otherfeedstuffs. During the ensiling process,ammonia, amines, amides, and nitrates

result from the degradation of proteinand can be used as nitrogen sources bythe rumen microbes.

The ruminant animal relies upon

microbial crude protein synthesized inthe rumen and dietary protein whichescapes digestion in the rumen for itssupply of amino acids. Microbial proteinis very high in quality, rivaling animalprotein and exceeding most vegetableproteins in essential amino acid content.However, the rumen microbes cannotproduce all the essential amino acidsrequired for animal growth and highlevels of milk production.

The amino acids are absorbed and

utilized in the small intestine. Mostamino acids are used in the synthesis of

body proteins, such as muscle and milkproteins. Some amino acids, especiallythose from protein reserves in the bodytissue, may be used to maintain bloodglucose levels and meet energy needs.

Lipids

Rumen microbes rapidly and extensivelymodify dietary lipids. Hydrolysis in therumen proceeds rapidly after ingestion.

The microbial metabolism of galacto-lipids (found in plant leaves) andtriglycerides (found in seeds) starts withtheir hydrolysis. The glycerol andgalactose portions are readily fermentedto VFAs. Liberated fatty acids areneutralized at rumen pH and adhere to

the surfaces of bacteria and feed par-ticles. The rumen microbes cannot usefatty acids as an energy source, and theiruse is restricted to cell incorporation and

synthetic purposes. Following thebreakdown of lipids, the microbes areresponsible for biohydrogenation, or theaddition of hydrogen to fatty acids withdouble bonds. An example would be themicrobial hydrogenation of oleic acid tostearic acid.

Vitamins

The rumen also functions in synthesizingB-complex vitamins and vitamin K. Thismakes the dairy cow less dependent on

dietary sources. If cobalt intake isadequate, then vitamin B

12is generally

not lacking. Additional supplementationof niacin or vitamin B

12may show a

production response, though sometimesonly in high-producing cows understress.

Basic nutritional concepts behind

feeding dairy cattleRuminants are excellent recyclers. Theyconsume fibrous feeds and waste by-products that are not suitable forconsumption by humans and single-stomached animals and convert theminto nutritious feeds like meat and milk.Table 8 lists feed sources that are utilized

by the ruminant.

Table 8. Feed ingredient sources that are utilized by ruminants.

FORAGE CROP FOOD-PROCESSING FIBER-PROCESSING PROTEIN ANIMALCROPS WASTES WASTES WASTES SUBSTITUTES WASTES

Legumes Straw Corn factory Wood fines Urea Blood meal

Grasses Cornstalks Apple pomace Paper Anhydrous- Meat meal

Corn silage Pea vines Beet pulp Cardboard Bone meal

Small grain Bean vines Brewers grain Cottonseed hulls Feather meal

Sorghum- Distillers grain Fish meal

Soyhulls

Oil meals

Bakery waste

Mill by-products

sudan

ammonia



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Table 9. Eating, rumination behavior, rumen pH, volatile fatty acids (VFAs), average milk yield, andmilk composition as influenced by particle size of the rat ion.

RATION

ITEM FINE MEDIUM COARSE

Eating, min./24 hr 195.3 204.4 204.7

Ruminating, min./24 hr 374.4a 466.3b 530.7c

Total chewing time, min./24 hr 569.7a 670.7b 735.4c

pH 5.3a 5.9b 6.0b

VFA, molar %

Acetic 58.33c 61.24d 61.82d

Propionic 22.34c 20.16c, d 19.46d

Actual milk, lb/day 69.3 70.6 68.4

4% FCM, lb/day 60.5a

66.6b, c

64.9a, c

Milk fat, % 3.0a 3.6b, c 3.8c

Milk protein, % 3.0 3.0 3.1

Source: Grant et al. 1990. Milk fat depression in dairy cows: Role of silage particle size. J. Dairy Sci.

73:183442.

Note: Rations formulated on 55:45 silage to concentrate basis consisting of alfalfa silage, high moisture

corn, and a mineral vitamin supplement. A field chopper with knives adjusted to a 3/16-inch theoretical

cut length and fitted with a 3-inch recutter screen chopped the fine silage. A 3/8-inch theoretical cut

length yielded coarsely chopped silage. A 1:1 mixture (dry weight) of the two silages provided the

intermediate particle length in the medium ration.

a, b, c, d Means within rows with unlike superscripts differ significantly.

Land that is not suitable for growingfood crops for human consumption can

be utilized to grow forage for ruminants.Perennial and annual forages, such as

alfalfa and corn silage, are low-cost andland-effective sources of nutrients.In order for the ruminant to utilize

these various sources of feedstuffs,certain basic rules for nutrition must befollowed to ensure optimum perfor-mance. The main concepts are related tofeed particle size, the structural andnonstructural carbohydrate fractions, andthe protein fractions supplied from thevarious feeds.

Adequate effective fiber is necessary

for proper rumen function. Rations fedwith insufficient forage particle lengthresult in cows spending less timechewing, which decreases the volume ofsaliva produced and leads to inadequate

buffering and lower rumen pH.When rumen pH falls below 6.0, the

growth of the cellulolytic organisms canbe reduced, allowing for an increase inthe propionate-producing microbes. Thiscan cause a decrease in the acetate topropionate ratio and potentially result in

a lower milk fat percentage.Particle size is important, especially

for forage utilization and maintenance ofa good fiber mat in the rumen. A fibermat is essential to assure adequategrowth and microbe activity and resultsin an increase of VFAs, especially acetate,and microbial protein yield. Table 9illustrates the influence particle size canhave on rumen function and productionparameters.

Feeding a ration with reduced forage

particle size will increase dry matterintake, decrease digestibility, and resultin lower rumen solid retention time.Rations that have a smaller initial forageparticle size will enter the rumen at aneven smaller size after initial chewingand swallowing, and therefore leave therumen at a faster rate. The result is anincrease in the rumen turnover rateallowing for an increase in dry matterintake, but because the rate of passage is


faster, less time is available for microbesto digest the feeds.

In addition to the forage particlelength, the fiber content in the diet isimportant. Fiber is necessary to provideadequate amounts of complex carbohy-drates to slow digestibility and controlthe acidity in the rumen. Acid detergentfiber and neutral detergent fiber (ADF,NDF) are the main fiber fractions that are

used in ration formulation. For high-producing, early lactation animals,recommendations are 18 to 20 percent ofADF and 28 to 30 percent of NDF in thetotal ration dry matter. The level offorage NDF and the forage particlelength in the diet play an important rolein determining effective fiber in the diet.However, not all fiber is of equal value inthe ration. See Carbohydrates (p. 13) formore in-depth information on forage

NDF and on the nonstructuralcarbohydrates.

The digestibility of the fiber willvary depending on the source. Forexample, fiber in some by-productingredients may be more digestible andmore quickly digested than forage withthe same fiber content. Fiber in low-quality forage may not be adequatelydigested. However, forages that are too

immature may be lacking adequate fiberand may be digested too rapidly.

The manner in which grains areprepared can have a substantial effect on

both the rumen environment and thecow. The particle size of the grains, suchas fine ground, coarse, rolled, or steamflaked, can affect the digestibility of thegrain and the total ration. The finer thegrind of a cereal grain, the more exposedthe endosperm of the grain, which allows


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for easier attack by rumen microbes.The type of heat processing influencesavailability of the starch (Table 10). Thisis associated with the gelatinization and

rupture of the starch granules as seen, forexample, in steam flaking. The method ofgrain processing, the amount of concen-trate fed, and the level of nonstructuralcarbohydrates (NSC) in the total rationdry matter have a tremendous influenceon animal performance.

There needs to be a balance betweenthe cell wall (NDF) and the cell contents(NSC) to maximize production as well asmaintain the health of the animal.Effective fiber is needed in the diet to

provide a fiber mat and to slow down theavailability of the carbohydrates to avoidlow rumen pH. The NSC or sugars andstarches are necessary to provide readilyavailable energy for the rumen microbesand the animal. Balancing rations too farin one direction or the other can bedetrimental to the dairy cow.

The main objective in balancing NDFand NSC is to control rumen pH. Theoptimum range in pH is 5.8 to 6.4 forsynthesis of microbial protein and

B-complex vitamins. This pH rangemay be somewhat higher or lower forshort periods of time throughout the day,especially in conventional feedingsystems. Ruminal pH normallyfluctuates less when cows are fed a totalmixed ration.

There are various ways to control thepH, such as providing adequate effectivefiber and providing a balance of proteinnitrogen, concentrate, fiber, and mineralsin the rumen. Much of the final outcome

of daily rumen pH level and fluctuationis determined by the feeding system andfeeding management practice. Inconventional feeding systems (thosewhere grain and forage are fed sepa-rately), implementing a feeding strategyis essential to eliminate the peaks andvalleys in rumen pH. Some commonrecommendations are feeding hay priorto concentrates, feeding high proteinforages and concentrates close to feeding

Table 10. Differences in extent of ruminal digestion of starches as affected by source and processing.

PERCENTAGEDIGESTIONINTHERUMEN

PROCESSING OATS WHEAT BARLEY CORN M ILO

Ensiled, high moisture

(fine grind) 99 99 98 85

Steam flaked

(thin flake) 99 98 97 86 84

Ensiled, high moisture

(coarse rolled) 82 80

Dry, fine grind 94 93 91 78 72

Dry, medium grind 89 88 87 74 68

Dry, coarse grind 79 78 77 65 61

Dry, whole 60

Source: H. H. Van Horn and C. J. Wilcox, ed. 1992. Nonstructural and structural carbohydrates.

In: Large Dairy Herd Management. Management Services, American Dairy Science Association,

Champaign, Ill., p 222.


of high energy feeds, and feedingconcentrates more than twice daily.

Buffers can aid in controlling rumenpH. Sodium bicarbonate is the mostlywidely used dietary buffer. Rationswhich benefit the most from buffers arerations containing a large percentage ofcorn silage and/or high moisture corn,

and low fiber forages.In addition to a good balance

between the carbohydrate fractions, thereneeds to be a balance between rumendegradable and rumen bypass protein tomeet the amino acid needs of high-producing cows. Bypass or undegradableintake protein (UIP) should range from35 to 40 percent for early lactation andhigh milk production (over 80 pounds ofmilk per day). Paying close attention tothe amino acid profile of bypass sources

of protein will help supply the essentialamino acids in the diet. However,

balancing for UIP alone is not recom-mended. Adequate degradable protein isnecessary so there are sufficient ammonialevels in the rumen to meet the nitrogenneeds of the microbes.

In order for the ruminant to functionproperly, the nutritionist must knowwhat substrates the rumen microbes aresensitive to so they can be avoided when

formulating rations. The rumen microbesare sensitive to both excessive anddeficient levels of protein, ammonia,urea, and the type and level of fat in theration. Mineral levels, especially calcium,phosphorus, sulfur, magnesium, copper,zinc, and cobalt, can cause problemswhen either too high or too low.

Abnormally fermented material mayalter the VFAs and lactic acid in therumen. This is more apt to occur if pH ormoisture contents of the material are outof the optimum range. Using feed spoiled

by mold, putrefaction, and mycotoxinsmay decrease production and mayincrease the incidence of displacedabomasum.

Water can have an effect on therumen microorganisms especially whenthere is heavy bacterial or metal contami-

nation or high mineral concentrationssuch as chloride. Water that is extremelyacidic or alkaline can also create prob-lems. It may be necessary to send watersamples out for analysis to check forabnormalities, especially when rations onpaper appear balanced but cows are notresponding accordingly.


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Dry matter i ntake and

its effect on the cowThe main objective in feeding manage-ment is to increase the dry matter intake

of the cows. With this increase shouldcome higher levels of milk production.In order for this to happen, close atten-tion to energy, ration digestibility, rumenfill, palatability, temperature, bodyweight of the animal, feeding conditions,environment, ventilation, frequency offeeding, and water intake and quality arenecessary. Establishing optimal standardsin each category should result in optimaldry matter intake.

Most lactating cows will eat to

satisfy energy needs if presented with asound and balanced ration. Yet cowsproducing over 85 pounds of milk oftencannot eat enough to meet their energyneeds. They may utilize body energyreserves, mostly fat, to make up at leastpart of any energy deficiency. One poundof body fat may be utilized to effectivelyproduce 7 to 9 pounds of milk, depend-ing on the fat test.

High-producing cows should be ingood body condition before they go dry.Table 11 gives the recommended rangefor body condition scores for the differentstages of lactation. Each score changerepresents 120 to 150 pounds of bodyweight gain or loss. Obesity should beavoided because cows will be moresusceptible to going off feed, ketosis,

calving difficulties, and more infectionssuch as mastitis. Low-producing andlate-lactation animals will sometimesconsume more feed than is necessary to

meet energy needs; thus body conditionshould be monitored closely with theseanimals. Dry cows may consume doubletheir needs if allowed to eat free choice.

When ration digestibility is too low,animals usually cannot eat enough tomeet their nutrient needs. If the energydensity in the diet is less than .66 McalNEL, then it may be impossible for high-producing cows to meet their energyrequirements.

Some rations that are relatively high

in digestibility may be consumed atlower levels since energy needs may bemet with less intake. High-quality rationsfor high-producing dairy cattle shouldcontain around .74 Mcal NEL. Rationscontaining too much concentrate and notenough forage and effective fiber mayactually depress intakes, milk produc-tion, and fat test and may adverselyaffect health. Ration digestibility mayalso be depressed by an improper

balance of nutrients. Low-quality forage

is a more frequent cause of loweredintakes and performance than the lack ofenergy in the concentrate portion of theration. Improper forage and grainpreparation may depress digestibility,performance, and sometimes total rationdry matter intake.

When feeding rations with lowdigestibility, rumen fill is quicklyachieved. These rations are digestedslowly and, to a lesser extent, pass out ofthe rumen at a slower rate. When rumen

fill occurs, a signal is sent to the brainstem to stop intake as part of the overallprocess of intake regulation.

The use of sodium bicarbonate orsesquicarbonate at .80 percent in the totalration dry matter can increase digestibil-ity by raising the rumen pH. This canresult in higher dry matter intakes. Anincrease in milk production and/or fattest may be noted when these additivesare fed.

Palatability is also a concern,especially in conventional feedingsystems. Certain feedstuffs and additivesmay depress intakes of concentrates

when fed conventionally compared to atotal mixed ration (TMR). For example,animal protein blends may have to belimited in the grain mix used on aconventional ration compared to higherlevels that can be fed in a TMR. Somespecies and varieties of forage are lesspalatable than others and may have to berestricted.

Both feeding conditions andenvironmental climate can limit intake.When the climate exceeds 65oF and 65

percent humidity, dry matter intake andoften milk production and fat test maydecrease. A substantial decrease in totalration dry matter may occur at over 80oFand 80 percent humidity. Thus there is aseasonal effect on dry matter intake withhigher consumption usually occurringduring cool weather and depressedintakes occurring during hot, humidweather. Forage quality and the energycontent of the concentrates as well as thedensity levels of protein, minerals, and

effective fiber generally need to beincreased during the summer months.Poorly ventilated feeding or housingareas can increase heat and humidity andallow strong odors, such as ammonia, to

become concentrated, which can cause adecline in consumption because animalsspend less time in those areas.

Dry matter intake can be depressedwhen heating, putrefaction, and moldoccur in ensiled feeds or TMRs. This can

be minimized by not removing ensiled

feeds from the silo much in advance offeeding. Ensiled feeds that have under-gone abnormal fermentation maydepress intakes. The presence of certaintoxins, such as mycotoxins, alkaloids,and tannin, can cause problems. In orderto minimize their effects on low perfor-mance, feed more often throughout theday, especially during the summer, tokeep feed fresh and from heating. Avoidusing problem feeds for milk cows,

Table 11. Target scores for stages of lact ationusing the 5-point body condition scale.

STAGEOF TARGETBODYLACTATION CONDITIONSCORE

Cows at calving 3+ to 4-

Early lactation 3- to 3

Mid-lactation 3

Late lactation 3 to 3+

Dry 3+ to 4-

Source: Body-condition Scoring as a Tool for

Dairy Herd Management. Penn State Extension

Circular 363.



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especially early lactation or high-producing cows.

Increasing feeding frequency maynot be necessary when feeding a bal-

anced ration that is managed properly.However, feeding more frequently thanone to three times daily may be necessaryin many situations to attain expectedtotal ration dry matter intakes, feedutilization, and production.


Water consumption and quality areoften overlooked as important factorsaffecting dry matter intake. In order foranimals to receive a plentiful and clean

supply of water, watering devices shouldbe functioning properly to allow ad-equate intake. The chemical and bacterialquality should be checked occasionallyfor possible contaminants.

A balanced ration will allow for

proper digestibility, good dry matterintakes, and satisfactory feed utilization.A ration should be developed withprofitable levels of milk production in

mind. In addition to balancing for themany nutrients, do not overlook thephysical aspects of the ration, such asminimum forage required, maximumlevels of concentrate to feed, effectivefiber, and palatability.


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PART II: FEEDAND FEED NUTRIENTSFOR DAIRY CATTLE

Many different feeds or combinations offeeds can be successfully used in rationsfor dairy cattle. Feed ingredients supplysources of nutrients, fiber, and particlesize necessary for normal digestion,metabolism, and performance. Becausefeeds vary in cost and nutrient content,good judgment must be used in theselection process. The type, source, andlevel of forages, roughages, concentrates,minerals, vitamins, and other additivesin the diet must be considered when

trying to meet the cows nutrientrequirements.

Forages are perennial and annualcrops grown for use as pasture, greenchop, haylage, silage, or hay that have

been harvested at the proper length. Theycontain significant levels of protein, fiber,energy, and vitamins A and E. If the cropshave been sun-cured, the feed may alsocontain significant levels of vitamin D.

Roughages are crops or processingwastes of adequate particle size that are

high in fiber, relatively low in energycontent, and devoid of fat solublevitamins A, D, and E. Cereal straw,cornstalks, cottonseed hulls, corn cobs, orapple pomace with hulls are commonroughages.

Concentrates are cereal grains andby-product feedstuffs containingrelatively high levels of energy. Gener-ally, concentrates are finer in particle sizethan properly harvested forages. Table 12shows the classification of commonlyused feed ingredients.

A dairy cows diet is usuallycomposed of various feed ingredientswhich can help meet her nutrientrequirements. However, no one nutrientis more important than another, and anexcess or deficiency of one or morenutrients can limit performance. Know-ing what nutrients feed ingredientssupply to a ration will help optimize feedutilization. The main nutrient categories

of importance in dairy cattle rations arecarbohydrates, fats, proteins, minerals,vitamins, and water. While fiber is not anutrient by strict definition, it plays acritical role in digestion and must beconsidered when formulating rations.

CarbohydratesCarbohydrates are the primary energysource for the ruminant andcan bedivided into two main fractions, struc-tural and nonstructural. The structural

portion of the plant is the cell wallmaterial and is analytically defined asneutral detergent fiber (NDF). NDFconsists of cellulose, hemicellulose,lignin, and a portion of the pectin. Forageintakes can be set using NDF whenformulating dairy rations.

Acid detergent fiber (ADF) isanother fiber value reported whichcontains only cellulose and lignin.Ruminants are unable to digest lignin;thus the higher the lignin content of afeed, the lower its digestibility. Thesecomplex carbohydrates are more slowlydigested and often less completelydigested than the nonstructuralcarbohydrates.

The simple or nonstructuralcarbohydrates (NSC) consist of the cell

contents, including sugars, starches,pectins, short chains of cellulose-likesubstances (-glucans), and in ensiledproducts, the fermentation acids. NSC isnot a chemically achieved value butrather is estimated as [100 - (CP + NDF +ether extract + ash)]. This type of

Table 12. Classificat ion of concentrate ingredients.

CPa UIPa SPa

> 40% > 45% OF CP > 30% OF CP

Corn gluten meal Blood meal Corn gluten feedUrea Corn gluten meal Whole cottonseed

Raw soybeans Fish meal Wheat midds

Canola meal Animal protein blends Raw soybeans

Cottonseed meal Brewers grains (wet and dry) Urea

Heat-treated soybeans Distillers grains

Soybean meal (44% or 48%) Heat-treated soybeans

NSCa FAT NDFa

>55% >18% >35%

Bakery product (i.e., bread) Chocolate Beet pulp

Barley Bakery waste products Corn gluten feedMilo Raw soybeans Distillers grain

Rye Whole cottonseed Wheat midds

Corn Candy waste products Brewers grain (wet and dry)

Hominy Tallow Whole cottonseed

Oats Heat-treated soybeans Soyhulls

Wheat

Source: Concentrates for Dairy Cattle. Penn State Dairy and Animal Science Extension Fact Sheet 94-06.

aCP = crude protein; UIP = undegradable intake protein; SP = soluble protein; NSC = nonstructural

carbohydrates; NDF = neutral detergent fiber. All values are listed on a dry matter basis.


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carbohydrate is highly digestible whencompared to NDF. Even though pectinsand -glucans are part of the cell wall,they are included in the NSC fraction

because they are rapidly fermented andeasily digestible (Table13).The amount of structural and

nonstructural carbohydrates in a rationcan have a profound effect on productionand health if not properly balanced in aration. The partitioning of the carbohy-drate fractions between plant species,especially legumes and grasses, isdifferent and can affect the extent andrate of digestion.

Comparing legumes and grasses of

similar maturities, legumes are generallyhigher in lignin and lower in NDF.Grasses tend to be higher in hemicellu-lose and NDF. The range for cellulose isfairly similar between the two types offorage (Table 14).

Since legumes tend to have a higherlignin content compared to grasses, lessNDF is available for digestion. Legumeshave a faster rate of digestion thangrasses, and therefore intakes are higherwith legume forages. The rate of diges-

tion is slower for grasses because theyremain in the rumen longer. Conse-quently, the total amount of digestion isgreater for grasses. Forage dry matterintake of predominantly grass foragescan be restricted while still maintainingadequate forage NDF intake (Table15).These differences between legumes andgrasses can influence how rations areformulated for forage NDF and foragedry matter intake.

The NSC fractions of forages can

also influence digestion. Pectins arefound in legumes but are negligible ingrasses. Pectins can ferment in the rumenas rapidly as starch, but they form acetaterather than propionate. -glucans, whichare a major component of grasses,ferment more slowly.

The NDF found in most concentrateingredients is less effective due to finerparticle size, greater density, higherdigestibility, and quicker passage from

Table 13. Carbohydrate fractions for some common forages and feed ingredients.

% OFNONSTRUCTURALCARBOHYDRATES

% DM BASIS PECTINSINGREDIENT NSC SUGAR STARCH -GLUCANS VFA

Alfalfa haylage 23.0 0.0 40.9 33.0 26.1

Grass hay 17.2 35.4 15.2 49.4 0.0

Corn silage 45.3 0.0 71.3 0.0 28.7

Barley 61.8 9.1 81.7 9.2 0.0

Corn 71.4 20.0 80.0 0.0 0.0

Hominy 59.9 8.9 80.4 10.7 0.0

Oats 42.4 4.4 95.6 0.0 0.0

Wheat 73.8 8.9 80.2 10.9 0.0

HMEC 70.8 0.0 94.8 0.0 5.2

HMSC 75.9 0.0 97.2 0.0 2.8

Canola 25.8 11.4 45.6 43.0 0.0

Distillers 10.3 0.0 100.0 0.0 0.0

Corn gluten feed 24.7 3.7 71.2 25.1 0.0

Corn gluten meal 17.3 0.0 69.4 30.6 0.0

Soyhulls 14.1 18.8 18.8 62.4 0.0

Soybean meal, 44% 34.4 25.0 25.0 50.0 0.0

Wheat midds 31.2 10.0 90.0 0.0 0.0

Source: Adapted from T. Miller, J. Grimmett, and W. Hoover, West Virginia University, 1993.

the rumen than forage NDF. Mostconcentrates are too fine in particle size

to provide a sufficient rumen mat,maintain normal rumen epithelial tissue,and stimulate sufficient chewing andeructation of gases. For these reasons, it isgenerally recommended that most of theNDF in the diet be in the form of forageNDF.

The NSC fractions of cereal grainsusually contain over 80 percent starch.Most by-product feeds contain a largerportion of the NSC fractions as starchwith the remainder as sugars and pectins.In concentrate ingredients, the availabil-ity and rate of digestion of the starchdepend on the grain source and process-ing method.

A good balance between thecarbohydrate fractions is necessary tomaintain normal rumen function andmetabolism (Table16). Extremes in eitherdirection can adversely affect animalperformance and health. For example, ifforages are chopped too fine, then the

effectiveness of fiber present in furnish-

ing a mat for microbial function andstimulating good rumen motility isreduced. Low digestibility of the foragealso may reduce the effectiveness of thefiber present. In order to keep the rumenfunctioning normally, minimum foragelevels and proper particle size length ofensiled forages must be ensured.

Low fiber, both ADF and NDF, in theration can result from lack of forage and/or extremely high-quality forage (mainlyearly spring or late fall cuttings). Lack of

fiber can lower milk fat test and produc-tion and cause metabolic problems, suchas rumen acidosis and infectious dis-eases. These problems can be controlled

by following sound guidelines for forageharvesting, forage particle size length,and forage NDF intake, and forage drymatter intake.

A proper intake of NSC is necessaryto provide sufficient propionic acidproduction to help meet the animalsenergy needs, allow for adequate



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Table 15. Guidelines for forage neutral detergent fiber (NDF) and forage dry matter intakes.

FORAGE NDF AS % OFBODYWEIGHTa INTAKELEVEL

.75%b Minimum if ration provides 1.3-1.4% total NDF by use ofby-product feeds.

.85%b Minimum if ration provides 1.0-1.2% total NDF by use ofgrains or starch feeds.

.90% Moderately low

.95% Average

1.00% Moderately high

1.10% Maximum

Source: Using Neutral Detergent Fiber to Set Forage Intakes for Dairy Cows. Penn State Dairy and Animal

Science Extension Fact Sheet 93-2.

aForage dry matter intake should range between 1.4 to 2.4 percent of body weight regardless of forage

NDF intake parameters.

bHigher minimum may be necessary if forage is chopped too fine.

Example of intake parameters between grass and legume forage:

Average body weight: 1300 lb; desired forage NDF as % BW: 0.90%

Legume hay @48% NDF; grass hay @62% NDF; 1300 X .009 = 11.7 lb forage NDF

Intake of legume forage: 11.7 .48 = 24.3 lb 1300 x 100 = 1.9% BW forage dry matter intake

Intake of grass forage: 11.7 .62 = 18.8 lb 1300 x 100 = 1.45% BW forage dry matter intake

Table 16. Guide to carbohydrate composition inrations for high-producing dairy cows.

STAGEOFLACTATION

ITEM EARLY M ID LATE

Forage NDF, % DM 21-24 25-26 27-28

Total NDF, % DM 28-32 33-35 36-38

NSC, % DM 32-38 32-38 32-38

Source: Use of Total Mixed Rations (TMR) for

Dairy Cows. Penn State Dairy and Animal Science

Extension Fact Sheet 94-25.

microbial protein synthesis, and maintainnormal fiber digestion as well as otherrumen functions.

Inadequate NSC may depress theenergy available from propionic andlactic acid production, reduce microbialprotein synthesis, and decrease fiberdigestion. Excessive NSC may depressfiber digestibility, acetic acid production,and milk fat test, as well as causeabnormalities in rumen tissue, whichmay lead to ulcers and liver abscesses.

FatsFat or ether extract can be used as an

energy source for the high-producingdairy cow. Fat is approximately 2.25times more energy rich than protein orcarbohydrates on a pound for pound

basis. Yet rumen microorganisms cannottolerate high levels of fat. The types andlevels of fats used in dairy cattle rationsshould be scrutinized closely bothnutritionally and economically.

The main lipid component of foragesis galactolipid, which involves glycerol,galactose, and unsaturated fatty acids(primarily linoleic and linolenic acid).Their concentration declines with the ageof the plant and will vary with theproportion of leaves to stems.

The main storage lipids found inboth plant seeds and animal fats aretriglycerides (three fatty acids attached toglycerol). Some of the specialty productslabeled as rumen inert are comprised ofeither triglycerides, free-fatty acids, orcalcium salts of fatty acids. The fatty acid

PART II: FEEDAND FEED NUTRIENTSFOR DAIRY CATTLE 15

Table 14. Fiber partition in various forages.

% DM BASIS

FORAGE % DM ADF NDF HEMICELLULOSE CELLULOSE LIGNIN

Legume

haylage 56a 34 44 10 27 7.451-62 30-38 36-51 5-14 23-30 5.7-9.0

Legumesilage 37 39 47 8.9 31 7.7

30-43 33-44 40-55 4.1-13.6 22-34 5.3-10.0

MM legumeb

haylage 55 37 48 11.5 29 7.851-60 31-42 40-56 5.7-17.3 25-33 4.3-11.4

MM legumeb

silage 35 39 52 13.4 32 6.827-42 35-42 45-59 7.8-18.9 29-35 5.4-8.3

MM grassb

haylage 59 38 54 15.7 31 7.752-65 34-43 46-62 10.8-21 27-34 5.5-9.9

MM grassbsilage 36 39 56 17.0 33 6.9

28-45 35-44 50-63 12-22 29-36 4.7-9.0

Grasssilage 31 41 62 21 24 6.4

21-41 37-44 55-68 15-27 31-37 4.9-7.8

Cornsilage 33 26 45 19 23 2.8

25-40 22-30 38-51 15-23 19-27 2.2-3.5

Note: Samples from NEDHIC Forage Testing Lab, Ithaca, N.Y. Analysis performed by J. B. Robertson,Department of Animal Science, Cornell University.aMean one standard deviation (range indicated by darker shading represents 67% of samples received)will fall within these values.bMM legume refers to mixed mainly legume forage; MM grass refers to mixed mainly grass forage.


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profile of vegetable, animal, and specialtyfats is an important characteristic becauseof how it relates to ruminal inertness andpostruminal digestibility (Table17).

Fatty acids can be either saturated orunsaturated. Common saturated fattyacids (myristic, palmitic, and stearic) aresolid at room temperature and melt atabove body temperature. Unsaturatedfatty acids (palmitoleic, oleic, linoleic,and linolenic) vary in melting point buttend to be liquid at room temperature.Unsaturated fats are more likely tointerfere with ruminal fermentation thansaturated fatty acids.

The fatty acids in whole cottonseed

and full-fat soybeans contain largeamounts of unsaturated fatty acids.However, whole oilseeds are less likely tointerfere with ruminal fermentationcompared to free oils. Whole oilseeds areslowly digested, allowing for a slowrelease of the oil in the rumen and moreextensive microbial hydrogenation.

Tallow is the most commonly fedanimal fat. It is comprised of about 50percent saturated fatty acids. Saturatedfats are believed to be relatively inert in

the rumen because of their high meltingpoint and low solubility in rumen fluid.However, 40 percent of the fatty acids intallow are oleic acid, which may impairrumen fermentation when added in largequantities.

Fatty acids in grease and animal-vegetable blends are highly unsaturated.Their fatty acid profiles can be quitevariable, and therefore they are notgenerally recommended for lactatingcow diets.

Specialty fats that completelybypass the rumen are highly saturated.Many of these products consist of tallowor hydrogenated tallow. Others havethe fatty acids complexed with calcium,which is relatively insoluble in rumenfluid.

To meet the essential fatty acid needsof the dairy cow, relatively low intakes offat are needed. In most cases, 2 to 3percent fat in the basal diet is adequate. A

Table 17. Fatty acid profile of various commodity and specialty f at sources.

COMMODITYFATSOURCES

FATTYACID WHOLE WHOLE YELLOW ANIMAL-WEIGHT, % COTTONSEED SOYBEANS TALLOW GREASE VEGETABLEBLEND

Myristic 1 3 3 1

Palmitic 25 11 26 18 22

Palmitoleic 6 4 5

Stearic 3 4 19 12 5

Oleic 17 24 40 47 36

Linoleic 54 54 5 13 29

Linolenic 7 1 3 2

Saturated, %a 29 15 48 33 28

Unsaturated, %b 71 85 52 67 72

SPECIALTYFATSOURCES

FATTYACID BOOSTER ENERGYWEIGHT, % ALIFET FAT CAROLAC DAIRY80 BOOSTER MEGALAC

Myristic 3 3 2 4 2 2

Palmitic 27 25 24 28 49 51

Palmitoleic 1 3 3 2

Stearic 37 22 35 55 35 4

Oleic 31 45 33 11 13 35

Linoleic 1 2 2 1 8

Linolenic 1

Saturated, %a 67 50 61 87 86 57

Unsaturated, %b 33 50 39 13 14 43

Sources: Palmquist, D. L. 1988. The feeding value of fats. In: Feed Science, ed. E.R. Orskov. Amsterdam:

Elsevier Science, 1988, pp. 293-311.

Palmquist, D. L., A. Kelbly, and D. Kinsey. 1989. Digestibility by lactating dairy cows of diets containing

two levels of several commercial fats. J. Dairy Sci. 72:572 (Suppl. 1).

DePeters, E. J., S. J. Taylor, C. M. Finley, and T.R. Famula. 1987. Dietary fat and nitrogen composition of

milk from lactating cows. J. Dairy Sci. 70:1192.

aSaturated fatty acids (Myristic, Palmitic, Stearic).

bUnsaturated fatty acids (Palmitoleic, Oleic, Linoleic, Linolenic).


tected fat. This would increase the totaldietary fat to 6 to 7 percent of the totalration dry matter.

When supplemental fat is added todairy rations, certain minerals must beadjusted. Modifications to the levels ofcalcium, phosphorus, and magnesiumare needed. It may also be necessary toincrease selenium and vitamin E. (SeeMinerals, p. 23, and Vitamins, p. 25.)

recommended limit for cows producingbetween 70 and 90 pounds of 4 percentfat-corrected milk is an additional 1.0 to1.5 pounds of added fat from unpro-tected sources, such as animal fats,oilseeds, or a combination of the two, can

be fed. This should result in an additional2 to 3 percent fat in the ration totaling 5percent. Cows producing over 90 poundsof 4 percent fat-corrected milk can be fedan additional .50 to 1.0 pound of pro-


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ProteinRuminant protein nutrition is compli-cated and requires examining proteinquality, protein fractions, and total

protein. Certain levels of degradable,soluble, and undegradable intake proteinmust be present in the dairy cows diet tomeet the needs of rumen microbes aswell as provide essential amino acids tothe small intestine.

Developing rations to meet the cowsrequirement for protein entails muchmore than balancing rations for totalcrude protein. The crude protein valuereported for forages and feeds is ameasure of their nitrogen content only; it

does not indicate whether the nitrogen iscontained as amino acid or true proteinnitrogen or some nonprotein nitrogensource. It also does not tell how degrad-able or available the nitrogen in the feedis for rumen microbes to synthesize, howmuch of the amino acid nitrogen in thefeed escapes degradation in the rumen,or the quality of this bypass protein. Allthese items need to be considered whenformulating rations.

The three protein fractions most

commonly used in ration formulationsare degradable, undegradable, andsoluble intake protein. The rumenmicrobes require an adequate supply ofruminally available nitrogen whichcomes from degradable sources ofnitrogen in feeds, including both proteinand nonprotein nitrogen sources. Inaddition, the rumen microbes benefitfrom a limited amount of the proteinreadily dissolving in the rumen. This isreferred to as soluble intake protein.Protein that escapes or bypasses therumen is referred to as undegradableintake protein.

When formulating rations, knowinghow feed ingredients will contribute tothe various protein fractions in a dairycows ration can be helpful for bettermeeting her protein requirements.Table 18 lists some of the crude proteinfractions in various feedstuffs commonlyfed to dairy cows.

Table 18. Crude protein and protein fractions in various forages and feed ingredients.

% OFCRUDEPROTEIN

CRUDE SOLUBLE UNDEGRADABLEFEEDSTUFF % DM PROTEIN PROTEIN INTAKEPROTEIN

Grass hay 90.0 10.5 29.0 37.0MM grass haya 90.0 12.5 30.0 34.0

Legume hay 90.0 18.6 32.0 28.0

MM legume haya 90.0 16.8 31.0 31.0

Grass silageb 55 41.0 45.0

MM grass silagea 55 42.0 42.0

Legume silage 55 48.0 36.0

MM legume silagea 55 46.0 39.0

Corn silage 33.0 8.8 48.0 31.0

Corn silage-urea 34.0 13.2 70.0 19.0

Corn silage-NH3

34.0 12.0 57.0 27.0

Blood meal 91.0 93.0 7.5 82.0

Brewers grain, dry 92.0 27.1 7.4 49.0

Brewers grain, wet 22.0 28.0 10.0 45.0Canola meal 92.5 40.8 28.0 23.0

Corn, ear (dry) 87.0 9.0 15.6 65.6

Corn, ear (high moisture) 69.0 8.8 36.0 35.0

Corn, shell (dry) 88.0 10.0 12.0 52.0

Corn, shell (high moisture) 74.4 9.5 33.0 35.0

Corn gluten feed 90.0 23.0 52.0 25.0

Corn gluten meal 90.0 67.2 5.0 55.0

Corn distillers, dark 91.0 29.0 15.0 47.0

Corn distillers, light 92.0 29.0 15.0 54.0

Cottonseed, whole 88.4 23.7 27.1 41.0

Soybeans, raw 90.0 41.8 40.0 26.0Soybeans, cooked 90.0 41.8 17.0 50.0

Soybean meal, 44% 90.0 50.0 20.0 35.0

Soybean meal, 48% 90.0 54.5 20.0 35.0

Wheat midds 89.0 18.0 40.0 21.0

Note: The expectancies on crude protein and protein fractions are provided for use when analyses are notavailable. If feasible, test concentrate ingredients as well as forages. These best-fit data have beendeveloped from Northeast DHI forage testing summaries and compilations by the National ResearchCouncil (NRC) and from the feed industry.

aMM grass refers to mixed mainly grass forage. MM legume refers to mixed mainly legume forage.

bUse the grass data for small grain silage.


% DM BASIS


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A more detailed description of theprotein fractions can be determined usingthe detergent system for analyses ofcarbohydrates along with the partition-

ing of protein by borate buffer. Theseprotein fractions are identified as fractionA (ammonia, nitrates, amino acids, andpeptides), fraction B1 (globulins andsome albumins), fraction B2 (mostlyalbumins and glutelins), fraction B3(prolamins), and fraction C (Maillardproducts bound to lignin).

Fraction A protein degrades in therumen instantaneously with nonereaching the small intestine. Smallamounts of fraction B1 reach the lower

digestive track with intestinal digestibil-ity being complete. The undegradableprotein fractions consist of variableamounts of B2 (30 to 70 percent), most ofB3, and fraction C. Fraction C bypassesthe entire digestion system. Heat addedor generated during the processing ofsome grains and by-products increasesthe bypass protein because globulins andalbumins in the B1 fraction are denaturedand are now in the B2 or B3 fraction.Table 19 lists the distribution of protein

and nitrogen fractions in some com-monly used feedstuffs. Although it isimportant to be aware of the detailinvolved with the various proteinfractions, at present most feed analysisreports and ration formulation programsdeal with target numbers related only tosoluble, degradable, and undegradableintake protein.

Balancing rations on protein qualitytends to be more complex compared tomeeting the animals requirement for

total protein and protein fractions.Attention to both microbial proteinproduction and the amino acid profile offeeds is needed.

Protein quality refers to the balanceand amount of essential amino acids thata particular feed contains. There areapproximately 23 different amino acids;each has a unique structure and allcontain nitrogen. Approximately

Table 19. Average distribution of protein and nitrogen fractions in some feedstuffs.

% DM BASISCRUDE

FEEDSTUFF PROTEIN A B1 B2 B3 C

Concentrates:

Blood meal 91.7 0.2 4.7 93.9 0.0 1.2

Brewers grain, dry 25.4 2.9 1.2 55.5 28.4 12.0

Canola 42.3 21.1 11.3 57.0 4.2 6.4

Corn grain 10.1 7.7 3.3 74.0a 10.0 5.0

Corn grain (high moisture) 10.1 40.0 0.0 44.1a 10.6 5.3

Corn, ear (dry) 9.0 11.2 4.8 66.2a 10.0 7.8

Corn, ear (high moisture) 9.0 30.0 0.0 51.3a 10.4 8.3

Corn distillers, dry 29.5 17.0 5.0 14.9a 43.1 20.0

Corn gluten feed 25.6 49.0 0.0 43.2a

5.7 2.1Corn gluten meal 65.9 3.0 1.2 84.8a 9.0 2.0

Cottonseed, whole 23.0 0.8 39.2 54.0 0.0 6.0

Cottonseed meal 44.8 8.0 12.0 48.4 2.4 7.6

Fish meal 66.6 0.0 12.0 87.0 0.1 0.9

Soybean meal, 44% 49.9 11.0 9.0 75 3.0 2.0

Soybean meal, 48% 55.1 11.0 9.0 75 3.0 2.0

Soybeans, raw 42.8 10.0 34.2 51.4 1.5 2.9

Soybeans, heated 42.8 5.7 0.0 70.7 16.3 7.3

Wheat midds 18.4 12.0 28.0 56.0 1.4 2.6

Forages:

Alfalfa hay, prebloom 21.7 28.8 1.2 55.0 5.0 10.0

Alfalfa hay, early bloom 19.0 28.8 1.2 52.2 7.8 10.0

Alfalfa hay, mid bloom 17.0 26.9 1.1 46.8 11.2 14.0

Grass hay, late vegetative 16.0 24.0 1.0 44.0 25.3 5.7

Grass hay, mid bloom 9.1 24.0 1.0 44.0 24.9 6.1

Grass hay, mature 7.0 24.0 1.0 44.0 24.5 6.5

Alfalfa silage, early bloom 19.0 50.0 0.0 23.3 11.7 15.0

Alfalfa silage, mid bloom 17.0 45.0 0.0 23.0 14.0 18.0Corn silage, 45% grain 9.0 45.0 0.0 38.6 8.5 7.9

Corn silage, 34% grain 8.6 50.0 0.0 34.0 8.0 8.0

Corn silage, 25% grain 8.3 55.0 0.0 29.0 7.5 8.5

Source: Russell, J. B., J. D. OConnor, D. G. Fox, P. J. Van Soest, and C. J. Sniffen. A net carbohydrate

and protein system for evaluating cattle diets: I. Ruminal fermentation. J. Animal Sci. 1992. 70:35513561.

aCorn products contain zein, a slow-degrading prolamine protein that is soluble in neutral detergent fiber.


% OFCRUDEPROTEIN


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10 to 13 amino acids must be supplied inthe ration and are designated as essential(Table 20). Some of the essential aminoacids, such as lysine and methionine, are

labeled as limiting amino acids. If theappropriate precursors, such as nitrogenand sulfur, are present in the rumen, thenessential amino acids can be synthesized

by the rumen microbes. This is one of theunique features of rumen microbes.

Microbial protein is high-qualityprotein because it has a good balance ofthe essential amino acids needed by thecow. Microbial protein contributes a largeportion of protein for the ruminantanimal to digest in the small intestine.

As much as 3.0 to 3.5 pounds of microbialprotein can be synthesized per day in the

rumen of a mature Holstein dairy cow.However, all the needs of a high-producing cow for essential amino acidscannot be met by microbial protein syn-

thesis alone. Certain essential amino acidsneed to be supplied in the ration, and asufficient proportion of this source mustescape or bypass rumen degradation.

Rations need to be balanced forthose essential amino acids that are likelyto be limiting under particular feedingsituations. Feed ingredients can vary intheir amino acid quality, and by incorpo-rating various sources dairy producerscan better meet the animals requirement(Table21). The most limiting amino acidsfor the high-producing dairy cow arelysine, methionine, and arginine.

Table 20. List of the essential and nonessentialamino acids.

ESSENTIALAMINOACIDS NONESSENTIALAMINOACIDS

Arginine (Arg) Alanine

Histidine (His) Aspartic acid

Isoleucine ( Ile) Citrulline

Leucine (Leu) Cysteine

Lysine (Lys) Cystine

Methionine (Met) Glutamic acid

Phenylalanine (Phe) Glycine

Threonine (Thr) Hydroxyglutamic acid

Tryptophan (Trp) Hydroxyproline

Valine (Val) Norleucine

Proline

SerineTyrosine


Table 21. The essential amino acid profiles of milk, ruminal bacteria, and feeds.

% OFTOTALESSENTIALAMINOACID

ITEM ARG HIS ILE LEU LYS MET PHE THR TRP VAL

Milk 7.2 5.5 11.4 19.5 16.0 5.5 10.0 8.9 3.0 13.0

Bacteria 10.4 4.2

from feed to milk

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