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1 Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061
2 Department of Animal and Dairy Science, Auburn University, Auburn, AL 36849
3 Department of Animal Science, Cornell University, Ithaca, NY 14853
4 Department of Dairy Science, University of Illinois, Urbana 61801
5 Department of Animal Science, University of Minnesota, St Paul 55108
6 Department of Dairy and Animal Science, The Pennsylvania State University, University Park 16802
7 Health and Nutrition Research Division, Eastman Chemicals Division Research Laboratories, Kingsport, TN 37662
Multiparous Holstein cows at six universities were utilized to examine effects of ruminally protected methionine and lysine on lactational performance. Three hundred and four cows began the study; 259 cows were included in the production analysis. Following a 21-d standardization period, cows received a basal diet of corn silage and ground corn supplemented with one of five dietary treatments, which were supplements of soybean meal or corn gluten meal, the latter with zero and three combinations of protected methionine and lysine (methionine; methionine and lysine; methionine and double (2x) lysine). Treatment effects were evaluated during early, mid, late, and total lactation (22 to 112, 113 to 224, 225 to 280, and 22 to 280 d post-partum respectively). On a DM basis, ratios of forage to concentrate (50:50, 60:40, and 70:30) increased, and dietary CP (16.0, 14.5, and 13.0%) decreased during the three periods of lactation. Amount of amino acid supplementation also decreased (15, 12, and 9 g/d methionine; 20, 16, and 12 g/d lysine; and 40, 32, and 24 g/d 2x lysine) with period of lactation. Actual and least squares means for milk, FCM, and milk protein yields were greater for soybean than for corn gluten meal during early, mid, and total lactation. In addition, these variables responded linearly to lysine in early lactation. Response to lysine was quadratic during mid and total lactation for these variables. Differences in nutrient intake explained production responses to protein sources but not to lysine. Serum amino acid responses primarily reflected differences in dietary protein source and rumen-protected amino acid.
Key Words: lysine and methionine • rumen protection • protein sources • lactational performance
Submitted on September 27, 1990
Accepted on March 4, 1991
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