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Testosterone Influences on Growth, Performance, Carcass Characteristics and Composition of Young Market Lambs¹

US Department of Agriculture^{2 , 3,}, Clay Center, Nebraska 68933

Abstract

Ram lambs, wethers and wethers implanted with Silastic capsules containing crystalline testerone were placed on test at 14.9 ± 1.1 kg and evaluated for differences in growth, performance, carcass characteristics and composition. Silastic implants that were able to maintain physiological concentrations of serum testosterone provided appropriate replacement therapy in wethers. Growth rate, efficiency of feed utilization and carcass yield of intact ram lambs and testosterone-implanted wethers were superior to the corresponding traits of wethers. Wethers had greater backfat thickness and percentage kidney and pelvic fat, and their carcasses graded higher than those of ram lambs or wethers implanted with a high dosage of testosterone. Empty body composition was significantly affected by treatment. Thus, intact rams contained more water and protein but less fat and gross energy than wethers. Testosterone-implanted wethers were intermediate in composition. Carcass water and protein were not significantly affected by treatment; however, carcass fat and gross energy were highest for wethers and lowest for intact rams. The relationship between testosterone and carcass fat and energy was dose dependent; i.e., decreased fat and energy were associated withincreased serum testosterone. In conclusion, testosterone appears to be the principal testicular hormone responsible for the superior performance and preferred carcass traits characteristic of young market rams.

¹ The authors acknowledge the technical assistance of Ms. Becky Weber, Mr. Lee Peshek, Mr. Brad Knapp and Mr. Wayne Hinerman and the cooperation of the Nebraska Agr. Exp. Sta., Univ. of Nebraska, Lincoln. Parts of these data were presented at the 1979 Annu. Meet, of the ASAS (Schanbacher et al, 1979), Univ. of Arizona, Tucson, July 28–31.

² Roman L. Hruska US Meat Anim. Res. Center, AR, SEA

³ Mention of a trade name, proprietary product or specific equipment does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products that may also be suitable.