Feedlot performance of the cows (Exp. 2) is shown in Table 5. Only main effects are reported because there were no interactions (P > .23). Testosterone treatment did not influence cow performance as it had influenced
heifer performance. They observed no effect of zeranol on mature cows but an 8% (nonsignificant) improvement with heifers. Lack of response to steroid implantation by mature animals has been observed by others. Daily gain decreased and feed effi- ciency was poorer (P < .05) as time on feed increased from 42 to 84 d. The live gain does not reflect carcass gain. From 42 to 84 d the cows gained live weight at .46 kg/d and carcass weight at 1.23 kg/d. The cows appa- rently had more rumen fill on d 42 than on d 84 as reflected in the lower dressing percent. Feed conversions were similar but were better than those reported by Matulis et al. (1987). Less time and fewer diets used by Matulis et al. (1987), when adapting cattle to the finishing diet, may have contributed to subacute acidosis and thus to the difference in response.