Meta-analysis of the effects of prepartum dietary protein on performance of dairy cows

摘要

The objectives were to review the published literatureand use meta-analytic methods to determine theeffects of dietary protein fed prepartum on productiveperformance of dairy cows. The hypothesis was thatresponses to dietary protein prepartum would differbetween nulliparous and parous cows, and performancewould be maximized at a greater protein supply innulliparous than in parous cows. The literature wassystematically reviewed, searching randomized experimentsin which the prepartum dietary content or degradabilityof protein was manipulated. Twenty-sevenexperiments including 125 treatment means and 1,801cows were included in the meta-analysis. Of those, 8 experimentswith 27 treatment means reported responsesfor 510 nulliparous cows. Data collected included theingredient composition and chemical analyses of prepartumdiets, parity group, and means and respectivemeasures of variance for productive responses. Mixedmodel meta-analysis was conducted and statisticalmodels investigated the effects of dietary crude protein(CP) or supply of metabolizable protein (MP) prepartumon performance. Supply of MP was predicted usingthe National Research Council Nutrient Requirementsof Dairy Cattle (2001) model. The mean ± standarddeviation and median (range) concentrations of dietaryCP fed to cows prepartum were 14.4 ± 2.2 and 14.4%(8.9 to 20.9%), resulting in mean and median (range)intakes of CP prepartum of 1,720 ± 432 and 1,734 g/d(745 to 2,482 g/d). Predicted prepartum supply of MPaveraged 822 ± 157 in nulliparous cows, ranging from517 to 1,094 g/d, and 1,146 ± 316 in parous cows, rangingfrom 463 to 1,733 g/d. Increasing prepartum CPcontent or predicted supply of MP improved postpartumdry matter intake in nulliparous cows, but increasingprepartum CP content reduced prepartum dry matterintake in parous cows. Yields of milk and fat-correctedmilk increased with increasing prepartum supply of MPin nulliparous but not in parous cows. Yields of fat andprotein increased in nulliparous cows with increasedCP content or supply of MP. Alternatively, in parouscows, yield of milk fat was not influenced by supply ofMP but responded quadratically to dietary CP contentand was maximized at approximately 14% CP. DietaryCP had no effect on protein yield in parous cows, butincreasing the supply of MP improved protein yieldonly in cows from experiments with >36 kg/d of milkproduction, whereas MP supply had no effect on proteinyield of parous cows from experiments with <28kg/d of milk production. Performance of dairy cows wasresponsive to prepartum supply of MP and nulliparousbenefited from diets with increased MP intake. Basedon current results, production responses for nulliparouscows increased linearly up to the maximum MP intakeof 1,100 g/d observed in the study, whereas for parouscows, only yield of milk protein in cows producing morethan 36 kg of milk/d was influenced by supplying morethan 800 g/d of MP.