THE INFLUENCE OF ZERANOL ON FEEDLOT PERFORMANCE AND CARCASS TRAITS OF CULLED COWS AND HEIFERS

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Abstract
A total of 126 cows and heifers culled from the University of Alberta beef herd were used in an experiment to study the effects of zeranol, an anabolic growth stimulant. The cattle were divided into two groups: 67 aged less than 4 yr (young) and 59 aged more than 4 yr (mature); within each group, three treatment levels of zeranol were applied (0, 36 or 72 mg/head of the commercial implant Ralgro®). All cattle were fed ad libitum a high-energy diet, and after 68 days the young group were slaughtered at a commercial packing plant; after a further 7 days the mature group were slaughtered at the same plant. Nine carcasses from each treatment level within the young group were fabricated into trimmed commercial cuts at the packing plant. Growth rates among double-implanted (72 mg) cattle were similar to those among single-implanted (36 mg) cattle; in the mature group, the growth rate was also similar in the control (0 mg) cattle. In the young group, implanting zeranol (36 mg or 72 mg) gave a 7–8% (P > 0.05) increase in growth rate. Zeranol caused no detectable changes in carcass traits or cut-out yields. Key words: Zeranol, cull cows, carcass traits