title: Supplementation of rumen-undegradable protein to the diets of early lactation Holstein cows on grass pasture.
abstract: The objectives were to evaluate supplements differing in rumen-undegradable protein (RUP) on the performance of early lactation cows on grass pasture. Twenty-four Holstein cows averaging 68 d of lactation and 39.8 kg/d of milk were rotationally grazed on predominantly Dactylis glomerata pasture for 8 wk. Cows were blocked according to parity, milk yield, and days of lactation and were randomly assigned to a grain mixture with a low or high RUP content. Pasture and the low and high RUP grain mixtures averaged 25.6, 14.7, and 13.7% crude protein and 4.0, 7.0, and 8.4% RUP, respectively (dry matter basis). Grain was fed twice daily at 1 kg/4 kg of milk, pasture provided all forage in the diet, and grain consumption was similar (8.9 kg/d per cow) for cows on both treatments. Total dry matter intakes estimated using chromic oxide were 19.9 and 20.9 kg/d for cows fed low and high RUP grain mixtures. Milk yields did not differ between treatments; means were 34.2 and 35.5 kg/d for cows fed low and high RUP grain mixtures. Multiparous cows tended to yield more milk (36.2 vs. 34.5 kg/d) and milk protein (1.06 vs. 0.98 kg/d) when fed the high RUP grain mixture. Concentrations of plasma urea N and nonesterified fatty acids were unaffected by treatment and averaged 18.7 mg/dl and 307 microeq/L, respectively. Results indicated that a supplemental grain mixture with a high RUP content did not alter milk yield of high yielding cows when pasture was the sole forage; however, milk protein yield tended to be greater for multiparous cows fed the high RUP grain mixture.
authors.affiliation: Department of Dairy and Animal Science, Pennsylvania State University, University Park 16802, USA.
authors.forename: D D
authors.initials: DD
authors.lastname: Hongerholt
authors.forename: L D
authors.initials: LD
authors.lastname: Muller
mesh_terms: D000821:Animal Feed; D000818:Animals; D001806:Blood Urea Nitrogen; D002417:Cattle / Q000502:physiology*; D004032:Diet; D004044:Dietary Proteins / Q000008:administration & dosage*; D019587:Dietary Supplements; D004063:Digestion; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D005285:Fermentation; D005983:Glutens; D007774:Lactation / Q000502:physiology*; D012417:Rumen / Q000378:metabolism*; D003313:Zea mays
chemical_list: D004044:Dietary Proteins; D005230:Fatty Acids, Nonesterified; D005983:Glutens