EFFECTS OF FEEDING MELENGESTROL ACETATE IN COMBINATION WITH DIETHYLSTILBESTROL AND ZERANOL IMPLANTS ON THE FEEDLOT PERFORMANCE OF FINISHING HEIFERS

Sixty yearling heifers were fed to compare the response of heifers implanted with 24 mg diethylstilbestrol (DES) to the response of heifers implanted with 36 mg zeranol, heifers implanted with DES and fed 0.4 mg melengestrol acetate (MGA) per day, and heifers implanted with zeranol and fed 0.4 mg MGA per day. All heifers were fed to appetite a ground snapped corn basal diet calculated to contain 11.6% crude protein, 10.3% crude fiber, and 67.5% total digestible nutrients. Feedlot performance and carcass characteristics of heifers implanted with zeranol, heifers fed MGA in combination with DES implants, and heifers fed MGA in combination with zeranol implants were not different (P > 0.05) from those of DES implanted heifers. Reproductive organs from heifers implanted with DES or zeranol were comparable to literature values for normal reproductive organs from untreated heifers. When either of these implants was used in combination with feeding MGA, follicle size and number of heifers with functional corporea lutea were similar to values reported in the literature when MGA was fed alone.