calf nutrition issues and factors affecting rumen development dr. howard tyler department of animal...
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Calf Nutrition Issues and Factors Affecting Rumen Development Dr. Howard TylerDepartment of Animal ScienceIowa State University
Meeting The Nutrient Requirements of the Calf A nutritionist’s nightmare Entire pre-weaning period is transition period
from non-ruminant to ruminant– proportions of nutrients provided by liquid vs. solid
feeds in constant flux– physical capacity of rumen increases
• potential for dry matter intake also increases
– fermentative capacity of rumen increases– absorptive capacity of rumen increases– therefore, digestibility of solid feeds also changes
as rumen develops
Energy Requirements
Approximately 20 kcal/pound of body weight in a thermoneutral environment for maintenance
Eighty pound calf requires 1500 kcal maintenance and 850 kcal for 0.5 lb of gain (2350 kcal/day total)
Requirements increase 1% for every degree below 500 F– High surface area:body mass ratio– Require 450 kcal more at 200 F (2800 kcal/day total)– Difference between ruminating calves and non-
ruminating calves– Difference between small and large calves
Body Size and Growth Rate Affects Protein Requirements The size of the calf affects the protein requirements
at any given level of intake– For 95 lb calf receiving 10 ounces of milk replacer twice
daily, a 20:20 milk replacer meets the protein needs– An 85 lb calf receiving the same amount of milk replacer
needs 22.5% protein, and a 75 lb calf needs 25% protein• Less energy needed from maintenance in lighter calves, so more
energy available for growth• Therefore, more protein required to support lean growth
Required protein:energy ratio needed changes with rate of gain targeted and size of animal being fed
Factors Affecting Protein Requirements Rate of gain determines amount of protein required
– If facilities, genetics, and calf source/management permit rapid gain, then high levels of protein and energy required in diet
– If facilities, genetics or calf source/management LIMIT rate of gain, then protein and energy must be reduced accordingly
The size of the animal affects the protein requirements at any given level of intake– Less energy needed from maintenance in lighter animals, so more
energy available for growth• Therefore, more protein required to support lean growth
Frequency of feeding affects digestive efficiency– Natural suckling frequency allows greater intake than most “hand-
feeding” systems can achieve– Required protein:energy ratio changes accordingly
Imbalanced Protein:Energy Ratios
If energy diverted to immune function (poor facilities), then it is NOT available for growth – Excess protein must be de-aminated and ammonia
detoxified and excreted• Energy required (3 ATP per molecule of urea) and
therefore even LESS energy available for growth and immunity
Overfeeding protein (in this case by underfeeding energy) impairs growth and may impair immunity
Is Mortality Rate an Issue? (Summary) Under excellent management conditions, there is no
evidence that calves fed higher levels of protein (appropriate for maximal growth rates) are at more risk or less risk for dying
Under marginal conditions, calves fed higher levels of protein may be at higher risk
Under highly challenging conditions, calves fed higher protein levels are at higher risk of dying than calves fed conventionally
This begs the question – do calves on a higher plan of nutrition have a stronger immune system or a weaker immune system?
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Does Higher Plane of Nutrition = Higher Functioning Immune System?
Challenges with Liquid Feeding Strategies
High energy intake from liquid feed delays initiation of starter intake and suppresses appetite for starter– high fat inclusions during cold weather– higher solids in the same volume of milk replacer– higher volume intakes
Must balance accelerated growth with accelerated rumen development
Establish Microbial Populations
After birth aerobic bacteria colonize Anaerobic bacteria soon dominate
– cellulolytic and methanogenic first– lactate-fermenting exceed adult values then
decline– protozoa introduction requires contact with
mature ruminants Influenced by access to solid feed and the
composition of the ration
Water Water availability may limit starter
intake– free water necessary for development of
rumen fermentative capacity• water in milk replacer bypasses rumen
The Rumen at Birth
At birth, the rumen and reticulum are under developed, sterile, and non-functional
Milk bypasses the reticulorumen by the esophageal groove
The reticulorumen comprises less than 1/3 of the entire stomach volume
The Rumen at Weaning
The rumen is the primary compartment (over ½ of stomach volume)
Size, metabolic activity, and blood flow have increased markedly
The rumen modifies both energy and protein prior to digestion by the calf
Absorptive Ability of Rumen Tissue
The rumen wall consists of two distinct layers:– musculature– absorptive epithelium
(mucosa) The mucosa is
responsible for absorbing VFA
Muscle is develops in response to material in the rumen
Development of the mucosa depends on the production of VFA
Roughage does NOT stimulate mucosal growth
Rumens of 4-Week-Old Calves
Milk, Grain, and Hay
Milk and Hay
What is the Right Balance?
Concentrates– VFA production
•butyrate
– High in energy•fermentable
carbohydrates
– Palatable
Forages– Low in energy
•structural carbohydrates
– Ruminal abrasion value (RAV)
– Bulk– Rumination
Starter Without Hay
Textured Commercial textured starter
Ground
CP - 23.58% ADF - 6.39%
CP - 25.44% ADF - 6.44%
Importance of Particle Size
Particle size of the diet influences– Palatability– Speed of digestion
• Rate of acid production
– Rumen retention time for digesta– Rumen pH via saliva production– Integrity of rumen papillae (RAV)
Starter With Grass Hay
Coarse + 7.5% HayHay of consistent particle size
Coarse + 15% Hay Hay of consistent particle size
CP - 23.08% ADF - 6.47%
CP - 22.60% ADF - 7.43%
Calf Starter with 7.5% Grass Hay
Increased body weight Increased feed efficiency Alters rumen VFA production
– increased acetate:propionate Creates a more stable rumen environment Decreased starter costs
– significantly improved feeding profitability– 4 lbs chopped hay per 50 lb bag of starter
Changes in Nutrients Utilized by Calves After Rumen Development
VFA are produced in the rumen and become an important source of energy
Blood glucose declines Ruminal bacteria increase
in population and become a primary source of protein– 50% protein– 80% digestible– High biological value
Weaning Strategies
Level of calf starter intake correlates with maturity of rumen fermentative function as well as physical development of rumen
Weaning should be intake-based Weaning reduces labor costs by 50%
and costs of gain by 3 to 5-fold– earlier weaning of healthy calves is most
profitable
Can A Ruminant Survive Without A Rumen??? Rumenectomies (early removal of the rumen) or
prolonged milk feeding used to answer this question– Young ruminants will survive for a time without rumen
fermentation– Animal viability decreases and sudden death occurs
between 6 and 8 months of age• Can be reversed almost immediately by providing food to the
rumen!!!
Ruminant animals “hard-wired” metabolically to function as ruminants– Must utilize the end-products of microbial fermentation
On raising calves
The first four weeks of its life the calf must receive the whole of its mother’s milk, because in this period the nutrition contained in the milk in so small volume can be replaced by no other equally nutritious and as easily digestible means of food.
After four weeks the milk may be replaced by that means of fodder which nutritious substance next to it in equal weight of dry volume, in the greatest possible amount.
USDA, 1847USDA, 1847