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Journal of Animal Science, Vol 75, Issue 11 3066-3073, Copyright © 1997 by American Society of Animal Science
JOURNAL ARTICLE |
R. H. Wessels, E. C. Titgemeyer and G. St Jean
Department of Animal Sciences, Kansas State University, Manhattan 66506-1600, USA.
We used the [15N]glycine single-dose urea end-product technique to measure whole-body protein turnover in six Holstein steers (250 +/- 18 kg). Steers were implanted with Revalor-S and continuously infused abomasally with water (4 L/d) or amino acids (AA; in 4 L/d water) in a crossover experiment (two 14-d periods). The AA infusion contained the following (g/d): lysine (5.3), methionine (3.3), threonine (3.2), tryptophan (1.0), histidine (2.1), and arginine (5.5). Steers were fed a diet containing 85% rolled corn, 10% prairie hay, and 1.1% urea (DM basis) at 2.16% of body weight. Nitrogen retention tended (P = .15) to increase with AA infusion, from 27.9 to 32.9 g N/d. Amino acid infusion numerically increased whole-body protein turnover from 168.6 to 183.2 g N/d, protein synthesis from 152.6 to 169.3 g N/ d, and protein degradation from 124.7 to 136.4 g N/d. Enhanced protein accretion may have resulted from a larger increase in protein synthesis than in degradation. The tendency for increased N retention is interpreted to suggest that the implanted, lightweight Holstein steers fed a corn-urea diet in our study were able to respond to AA supplementation, suggesting that at least one of the infused AA was limiting in the basal diet. Protein turnover data suggest that cattle, like other animals, may increase protein synthesis and protein degradation in response to supplementation with limiting AA. The [15N]glycine single-dose urea end-product technique for measuring whole-body protein turnover in cattle may be useful.
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