ideal concentrate feeds for grazing dairy cows

8/12/2019 Ideal Concentrate Feeds for Grazing Dairy Cows

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Limitations have been imposed on

intensive milk production systemswith the introduction of milk quotas,the necessity to take into account environ-mental concerns and the GATT proposals.These limitations increase pressure on milkprices and lead to an increased emphasis onproduction efficiency. Despite some differ-ences in the grass-growing seasons betweenEuropean countries, grazing should formthe basis of sustainable dairying systems inthe future. Grazing is the cheapest source ofnutrients for dairy cows and contributes tothe competitiveness of milk production,preserves the rural landscape and projects agood image of dairy production.

Full exploitation of grazing will requiredevelopment of grazing systems designed tomaximise daily forage intake per cow andimprove the efficiency of nutrient usethrough supplementary feeding.Supplements are generally provided to graz-ing dairy cows to increase total energyintake and animal performances above thatwhich can be produced from pasture alone.However, the efficiency of supplementation(in kg increase in milk per kg increase insupplement DM intake) is largely dependentupon the effect of supplementation on for-age intake and the objective is now todefine the conditions where use of supple-

mentary feeds will minimise the reductionin forage intake.

Milk yield with and withoutsupplementsMilk yield in unsupplemented cows increas-es by 1.0 kg/day for every 4 kg increase inherbage allowance (Delaby et al., 1999).However, increased herbage allowance inearly season also increases residual swardheight, and this may result in a deteriora-tion of sward quality in mid and late season.From a practical point of view, there is notmuch room for manoeuvre. Hoden et al.(1991) and Delaby et al. (1999) found that

milk yield can be increased by no more than1.5 kg/cow per day by increasing herbage

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Ideal concentratefeeds for grazing

dairy cowsGrazing is a valuable, low cost resource for feeding

high-yielding dairy cows. However, the balance between

providing sufficient energy and managing grassland is

delicate. Full exploitation of grazing systems to maximise milk

yield requires that concentrate feeding is also optimised.

By Jean Louis Peyraud

There is a delicate balance between conserving grazing resources, adding supplement andmilk yield. (Photo Theo Tangelder)


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allowance in spring without very seriouseffects upon sward quality later in the sea-son. Feeding supplements is a more power-ful tool to control performance.

It has long been generally accepted that

concentrates are not very efficient at graz-ing, with an average response of 0.4 to 0.6

kg milk per kg DM of concentrate, mainlybecause feeding concentrate generallyreduces herbage intake. From two compre-hensive reviews of the literature we showedrecently that the efficiency of supplementa-

tion (Table 1) and the substitution rate (0.4 0.3; n = 57; Delagarde and Peyraud, unpub-

lished) are quite variable, indicating highresponses can be achieved in some circum-stances. Indeed, milk responses to concen-trate are higher in data published after1990. The incremental increase in milkresponse averages + 0.1 kg/ kg DM concen-trate every ten years. Indeed, overall effi-

ciencies close to or higher than 1.0 kg ofmilk per kg DM concentrate were recentlyreported when less than 4.5 kg of concen-trate are provided to cows producing morethan 25-30 kg milk at turnout (Table 2). It isprobable that these higher responses arerelated to the genetic merit of the cow thathas appreciably increased since the earlybibliographical reviews.

The response of milk yield to incrementalsupplementation does not vary with thepotential of the animals as observed atturnout (from 25 to 40 kg milk) when alloca-tion of concentrate is constant betweencows, at least up to levels of 4-6 kg of con-

centrate (Delaby et al., 2001). This probablyreflects the inability of the cows to covertheir requirements with herbage alone evenfor the moderate producing animals whichare far from reaching their expected milkyield and the ability of high producing cowsto increase herbage intake according totheir potential yield. The incrementalincrease in intake averages 250 g OM / kgexpected milk yield (eMY; Peyraud et al.1996). Whether these identical responsesbetween cows also apply at higher concen-trate allocation is unknown but responsesto concentrate might decrease progressivelyfor higher levels of concentrate in low pro-

ducing animals when they reach theirexpected milk yield.

Interaction between supplement andgrazingDelagarde and Peyraud (unpublished) sum-marised the responses of 48 grazing experi-ments in which the net energy balance ofthe unsupplemented cows was calculatedfrom measured herbage intake, grassdigestibility and milk yield. They demon-strated that the substitution rate betweengrass and concentrate is poorly related tothe level of concentrate but is primarily afunction of the net energy balance (EB in

MJ/day) of unsupplemented cows (Figure 1).In practice energy balance may differ

according to the amount of grass ingested.This explains why numerous studies haveconcluded the substitution rate is positivelyrelated to herbage allowance, herbageintake increasing with increased herbageallowance. For the same reason, the substi-tution rate between fresh grass and con-served forages dramatically increases whensward surface height increases. In ourexperiments, there was a linear response inmilk up to 6kg of concentrate when herbagewas restricted, whereas at high allowancethe response reached a plateau after 4 kg of

concentrate (Figure 2).Energy balance may also differ according

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Table 1 - Response of milk yield, protein and fat content of milk toconcentrate supplements (after Delaby and Peyraud,unpublished)

n Mean Min MaxAll dataConcentrate intake (kg DM/day) 141 2.8 1.2 0.90 5.90

Milk (kg/kg DM concentra te) 141 0.66 0.46 - 0.56 2.39Protein conten t 107 0.23 0 .32 - 0.52 1.34(g/kg per kg DM concentra te)Fat content 133 - 0.29 0.53 - 1.92 1.06(g/kg per kg DM concentra te)

Data published after 1990Concentrate intake (kg DM/day) 55 2.9 1.2 0.90 5.40

Milk (kg/kg DM concentra te) 55 0.89 0.43 - 0.18 2.00Protein content 54 0.20 0.29 - 0.51 0.81(g/kg per kg DM concentra te)Fat content 54 - 0.21 0.46 - 1.25 0.80(g/kg per kg DM concentra te)

Table 2 - Effect of the amount of concentrate on milk response toconcentrate supplements in grazing dairy cows

Concentrate Global Efficiency Marginal(kg DM/day) (kg milk/kg concentrate) efficiency

C M H 0 to M 0 to H M to H Authors

0.9 2.6 4.3 0.8 0.5 0.2 Meijs and Hoekstra (1984)

0 1.8 3.5 1.4 0.9 0.4 Wilkins et al. (1994)0 1.8 3.6 0.9 0.7 0.6 O Brien, Crosse a nd Dillon (1996)0 1.8 3.6 1.3 0.9 0.5 Delaby and Peyraud (1997)0 1.8 3.6 0.7 0.6 0.5 Dillon, Crosse, and O Brien (1997)0 3.4 6.7 0.9 0.8 0.7 Robaina et al. (1998)0 2.7 5.4 1.1 1.0 1.0 Delaby, Peyraud and Delagarde (2001)

C : control, M : me dium, H high level of concentrate

Figure 1 - Effect of the level of supplementation and energy balance on thesubstitution rate be tween fresh grass and concentrate (afterDelagarde and Peyraud, unpublished)


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to the quality of grass, so substitution rate ispositively related to herbage digestibility(Grainger and Mathews, 1989). This alsoexplains why milk response can increaseduring the grazing season when grass quali-ty and availability are lowered. For a givenstocking rate, the method of grazing doesnot affect the performance of dairy cowsand thus the energy balance of the cows(Hoden et al. 1987, Le Du, 1980). Thereforeresponses to concentrate are similarbetween rotational grazing systems inwhich fresh pasture is allocated either daily(strip grazing) or over several days (paddock

system) (Hoden et al. 1987). Responses arealso similar between rotational and contin-uous grazing systems (Arriaga Jordan andHolmes, 1986).

Nature of the supplementHerbage intake is more drastically loweredwhen cows are supplemented with foragesthan with concentrates (Mayne and Wright,1988). On good grazing conditions, whenthe supply of fresh grass is large, giving con-served forages (grass silage, hay or maizesilage) as a buffer feed, results in large sub-stitution rates, often over 1.0. In these situa-tions, very low milk responses or even a

decrease in milk yield compared to controlcows were obtained (Leaver, 1985) becausenet energy content is lower in conservedthan in fresh forages. The substitution ratebetween fresh grass and buffer foragesdecreases to 0.3 when the availability offresh forage is restricted. Thus forage sup-plements must be provided only duringperiods of grass shortage or in the areaswhere availability of grass is not sufficient.The response to supplementary forage isthen much higher in summer than inspring (Phillips and Leaver, 1985). The largesubstitution rates obtained with foragesappears to be mediated by a large reduction

in grazing time which can reach 40 min/kgof silage DM (Mayne, 1991) whereas the

reduction in grazing time per kgDM of concentrate averages 10 to15 min.

In the current context of dairyproduction, it is generally assumedthat energy is the first factorwhich limits animal performancesat grazing. Readily fermentablestarch (barley, wheat) is generallyconsidered to decrease milk fatcontent and acetate:propionateratio in the rumen compared tofibre concentrate or less readilyfermentable starch (maize). Indeed,

energy source in the concentratehas little effect on milk output andcomposition when moderate levelsof concentrate are fed. Compared to 3.5 kgof wheat, feeding 3.5 kg of a concentraterich in soya-bean hulls, which is a slowlydegraded cellulose increased milk fat con-tent (+ 1.3 g/kg, Table 3) and marginallydecreased protein content (- 0.5 g/kg)(Delaby and Peyraud, 1994).

In most cases milk production from pas-tures is not limited by metabolisable pro-tein (MP) supply but in some circumstancesthe crude protein content of grass candecrease and the supplementation with MP

may be beneficial. This might occur when Nfertilisation is reduced or during summergrazing. Delaby et al. (1996) described theresponse curve of milk yield when increas-ing MP was provided by progressively replac-ing 3 kg of wheat by protected soya-beanmeal. On highly N fertilised sward, withcrude protein content greater than 160 g/kgDM, milk yield marginally increases withMP supply whereas on low N fertilisedsward, with crude protein content lowerthan 130 g/kg DM, the response is markedlygreater (Figure 3). The provision of 600 g/dayof supplementary MP produced similar milkyield to that obtained with high-fertilised

sward without MP supplementation. Thelower the protein content of grass the high-

er the response to the MP supplementation.On low N sward, the replacement of car-

bohydrate concentrate by protected soybeanmeal makes it possible to increase theamount of ingested forage. Delagarde, et al.(1999) reported an increase in herbageintake (+ 0.8 kg / kg concentrate) when cowsare supplemented with protected soybeanmeal (Table 4). This positive effect of MPsupplementation on grass intake is clearlyattributable its low protein content as it waspreviously observed with poor quality con-

served forages (Journet et al. 1983). Thus, onlow N sward, MP supply increases milk yieldbecause it alleviates a shortfall in MP supplybut part of the increase in milk yield canalso be assigned to an increase in herbageintake. At pasture with high crude proteincontent, MP supply in the concentrate hasgenerally no large effect on herbage intake(Vadiveloo and Holmes, 1979; Delagarde etal., 1997).

Supplementation strategiesSupplementation can be administered asconstant single doses to all cows whateverthe milk potential or computed as a func-

tion of the cows potential: the higher thecow potential the higher the level of con-

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Figure 2 - Interaction between the level of concentrateand herbage allowance on milk response tosuppleme ntation (after Delaby e t al. 200 1 experiment 1)

Figure 3 - Interaction between the grass crude proteincontent and the response tosuppleme ntation with m etabolisable protein(after Delaby et al. 1996)

Table 3 - Effect of the nature of energyon m ilk yield by dairy cowsgrazing on vegetative perennialryegrass swards (after Delaby etal. 1994)

Wheat Dried Soya beanBeet Pulp hulls

Milk yield (kg/day) 26.7 27.2 27.3Protein content (g/kg) 30.0 29.4 29.5

Fa t content (g/kg) 36.2 36.6 37.5

Intake of concentrate : 3.5 kg DM/day


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centrate allocated (Hoden et al. 1991). Thislatter strategy assumes a cow is unable toadjust her grass consumption according to

requirements. Delaby and Peyraud (1997)compared 3 kg of concentrate administeredeither at a constant rate for all cows or at arate of 1 kg of concentrate for each 3 kg ofmilk above 20 kg of milk at turnout, observ-ing similar animal performances. Thus it ispossible to use a single dose of concentratefor all dairy cows, if grazing conditionsfavour maximum grass intake.

Theoretically, increased frequency of con-centrate feeding should result in less diur-nal variations in ruminal pH (Sutton et al.

1986), which in turn might increase theamount of grass a cow can consume andthus animal performance. On pasture, grainis normally fed twice daily to cows, duringor after milking. Recently some mobile com-puterised grain feeders were developed tomanipulate the temporal pattern of supple-mentation for cows fed with more than 8 to10 kg DM of concentrate. Cows tend to con-

sume less concentrate with the grain feederdue to missing occasional meals and thishad resulted in lower milk yield

(Hongerholt et al., 1997; Gibb et al., 2000).But even for cows which have consumed thesame amount of concentrate in the parlourand from the grain feeder, increasing thefrequency of concentrate meals did notimprove animal performance.

References are available on request.

Table 4 - Effect of energy and protein source on herbageintake and digestion by dairy cows grazing onplots of perennial ryegrass with a low CPcontent (after Delagarde, et al. 99)

No En erg y So yb ea n

concentra te mea l

Concentra te intake (kg DM/day) 0 2.8 2.8Gra ss intake (kg DM/day) 14.6 14.9 17.2Gra ss digestibility 0.774 0.761 0.793Rumen VFA (mmoles/l) 99 101 111

NH3 (mg/l) 11 11 21Protein flow ing into the duodenum (kg /da y) 2.2 2.5 3.5Milk yield (kg/day) 19.6 22.0 24.8

Figure 4 - The benefits of grazing and supplementsalso depend on the cows genetic potential

ideal concentrate feeds for grazing dairy cows

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