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Effect of Protein Level in Prepartum Diets on Metabolism and Performance of Dairy Cows¹

A. F. Park^*, J. E. Shirley^*, E. C. Titgemeyer^*, M. J. Meyer^*, M. J. VanBaale^* and M. J. VandeHaar

^* Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-1600
Department of Animal Science, Michigan State University, East Lansing 48824

Corresponding author:
J. E. Shirley; e-mail:
jshirley{at}oznet.ksu.edu.

Multigravid Holstein cows (n = 75) were used in a randomized block design to evaluate the effect of prepartum diets formulated to supply surplus energy and incremental concentrations of protein on the nutritional status of dairy cows at parturition. Cows were blocked according to expected calving date and assigned to one of five diets: 9.7, 11.7, 13.7, 14.7, and 16.2% crude protein (CP). Dietary treatments were initiated 28 d before expected calving date and fed until parturition. A common diet was fed postpartum. Dry matter intake and milk yield were recorded daily through 90 d postpartum. Increasing the protein concentration from 9.7 to 14.7% of dry matter during the last 28 d of gestation improved responses of cows during lactation. Increasing dietary protein up to 14.7% also increased milk yield response to recombinant bovine somatotropin (rbST) during the ninth week of lactation and yields of 305-d 2x mature equivalent milk, milk protein, and milk fat. Plasma aspartate aminotransferase tended to be highest in cows fed 13.7 and 14.7% CP prepartum, but decreased linearly postpartum in response to dietary protein levels. There were no treatment differences for plasma insulin-like growth factor-1 (IGF-1) at d 60 postpartum (before rbST provision), but IGF-1 on d 90 (after rbST provision) was higher in plasma of cows fed 14.7% CP than the other diets except 13.7% CP. Close-up diets containing 13.7% CP and surplus energy produced the most beneficial outcomes during the subsequent lactation.

Abbreviation key: AST = plasma aspartate aminotransferase, , EB = energy balance, , ECM = energy-corrected milk yield, , MUN = milk urea nitrogen, , PME = previous 305-d 2x mature equivalent milk yield, , PUN = plasma urea nitrogen

Key Words: periparturient • protein • body condition • prepartum

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