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Feedlot Performance and Blood Plasma Amino Acid Patterns in Beef Steers Fed Diethylstilbestrol Under Ad Libitum, Restricted, and Compensatory Conditions

Nutrition Institute, Ruminant Nutrition Laboratory, Agricultural Research Center, Agricultural Research Service, U. S. Department of Agriculture, Beltsville, Md. 20705

The purpose of this study was to determine the influence of diethylstilbestrol (DES) and widely differing nutritional regimens on the feedlot performance and blood plasma amino acid patterns of beef steers. Sixteen 276-kg steers were fed a high protein finishing diet ad libitum for 28 days, then feed was restricted to 2 kg/steer/day for 35 days and finally again fed ad libitum for another 60 days. Eight steers were given 20 mg DES daily during the complete study. Feeding 20 mg of DES resulted in a marked (P < 0.01) improvement in animal performance during ad libitum feeding conditions. Feeding DES during the period of feed restriction, however, caused a greater (P < 0.05) animal weight loss. The concentrations of all of the individual amino acids differed (P < 0.01) because of the feeding regimen except for hydroxyproline, asparagine plus glutamine, and cystine. For the complete study, feeding DES resulted in lower (P < 0.01) concentrations of urea, proline, valine, phenylalanine, total essential amino acids and lower (P < 0.05) concentrations of serine, glutamic acid, alanine, methionine, leucine, lysine, arginine and total nonessential amino acids. The effect of DES on amino acid concentrations was essentially the same irrespective of feeding regimen except for asparagine plus glutamine, which was markedly increased during feed restriction. More than 2 days was required for the response to DES or a changing feeding regimen to be reflected in stable blood plasma amino acid patterns.

KEY WORDS: • beef steers • DES • amino acids • feedlot performance

¹ Present address: University of Nottingham, School of Agriculture, Sutton Bonington, Loughborough, Leics, England.

² ARS, Biometrical Services.

Manuscript received 6 November 1972.