Supplementation of Rumen-Undegradable Protein to the Diets of Early Lactation Holstein Cows on Grass Pasture

¹ Department of Dairy and Animal Science, The Pennsylvania State University, University Park 16802

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 µeq/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.

Key Words: pasture • lactating cows • rumen-undegradable protein • grain supplementation

Submitted on November 5, 1997
Accepted on April 13, 1998

This article has been cited by other articles:

				I. R. Ipharraguerre and J. H. Clark Impacts of the Source and Amount of Crude Protein on the Intestinal Supply of Nitrogen Fractions and Performance of Dairy Cows J Dairy Sci, May 1, 2005; 88(e_suppl_1): E22 - E37. [Abstract] [Full Text] [PDF]

				J. H. Fike, C. R. Staples, L. E. Sollenberger, B. Macoon, and J. E. Moore Pasture Forages, Supplementation Rate, and Stocking Rate Effects on Dairy Cow Performance J Dairy Sci, April 1, 2003; 86(4): 1268 - 1281. [Abstract] [Full Text] [PDF]

				F. Bargo, L. D. Muller, E. S. Kolver, and J. E. Delahoy Invited Review: Production and Digestion of Supplemented Dairy Cows on Pasture J Dairy Sci, January 1, 2003; 86(1): 1 - 42. [Abstract] [Full Text] [PDF]

				F. Bargo, L. D. Muller, G. A. Varga, J. E. Delahoy, and T. W. Cassidy Ruminal Digestion and Fermentation of High-Producing Dairy Cows with Three Different Feeding Systems Combining Pasture and Total Mixed Rations J Dairy Sci, November 1, 2002; 85(11): 2964 - 2973. [Abstract] [Full Text] [PDF]