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Journal of Animal Science, Vol 75, Issue 11 3038-3045, Copyright © 1997 by American Society of Animal Science

JOURNAL ARTICLE

Nitrogen metabolism and hormonal responses of steers fed wheat silage and infused with amino acids or casein

K. K. Ragland-Gray, H. E. Amos, M. A. McCann, C. C. Williams, J. L. Sartin, C. R. Barb and F. M. Kautz
Animal and Dairy Science Department, The University of Georgia, Athens 30602-2771, USA.

Four Holstein steers (159 kg) surgically fitted with abomasal-infusion cannulas were used in a 4 x 4 Latin square study to test amino acid (AA) and casein (CAS) infusions on nitrogen balance and hormonal status of steers consuming vegetative wheat (Triticum aestivum L.) silage (12.3% CP). Treatments were 5-d infusions of 1) water (CONT), 2) arginine (ARG; 13.69 g/d), 3) limiting amino acids (LAA, 13.69 g/d arginine + 10.92 g/d histidine + 28.97 g/d lysine + 10.88 g/d methionine + 16.96 g/d threonine, and 4) Na-CAS (300 g/d). Whole blood was collected for plasma AA, growth hormone (GH), insulin, and IGF-I concentrations. Data were analyzed by ANOVA, and the following orthogonal contrasts were used to separate treatment means: CONT vs ARG; ARG vs LAA; and LAA vs CAS. Urinary N increased (P < .02) for CAS vs LAA. Arginine increased N retention, as did CAS, compared to LAA. Total plasma essential AA were decreased by arginine. Mean plasma insulin concentrations were increased by CAS (P < .034). Arginine increased mean plasma GH levels, but not IGF-I. The CAS treatment increased (P < .015) IGF-I levels, but not GH. These data suggest that performance of steers fed wheat silage was limited by duodenal AA flow and that arginine was the first-limiting AA. Casein infusion increased plasma insulin and IGF-I, which would explain the improved growth noted in calves and lambs fed forages supplemented with ruminally undegraded protein.


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Copyright © 1997 by the American Society of Animal Science.