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Influence of Sex, Stilbestrol Treatment and Slaughter Weight on Performance and Carcass Traits of Slaughter Lambs¹

Texas Agricultural Experiment Station, San Angelo (76901) and College Station (77840)

Abstract

A total of 196 crossbred lambs out of Rambouillet ewes were early weaned and fed to slaughter on high energy rations. These lambs consisted of males, females, wethers and wethers receiving stilbestrol. The lambs were slaughtered at weights ranging from 36 to 64 kilograms. The data were analyzed within sex-treatment subgroups as to the influence on slaughter or carcass traits. Important differences were observed in rate of gain, feed efficiency and rate of change in feed efficiency with increases in body weight. Ram lambs gained significantly faster and more efficiently to heavier weights than females and wethers. Stilbestrol-treated lambs tended to approach ram lambs in both respects. Mean values are reported for various carcass traits for the sex-treatment groups adjusted to an equivalent carcass weight of 24 kilograms. Significant differences were observed for all traits except U.S.D.A. quality and final grade and shear force value. The differences tended to be related to differences in amount of fat in the carcass and the percent of weight in the fore and hindsaddle. Males and stilbestrol-treated wethers had a higher percent of the carcass weight in the foresaddle; whereas, in the case of the females and wethers a higher percent of the weight was in the hindsaddle. Correlation and regression coefficients (linear and quadratic) are reported to indicate the rate of change in various carcass traits with increasing carcass weight. These data indicate that males can be fed to heavy weights without excessive fat deposition; whereas, under the management system employed in this study, female lambs became excessively fat at weights below 40 kilograms. Wethers or stilbestrol-treated lambs were intermediate in these respects.

¹ T. A. 9261, Texas Agricultural Experiment Station.