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Effects of Melengestrol Acetate on the Performance of Feedlot Cattle Receiving Corn Silage Rations^{1, 2, 3,}

Michigan State University, East Lansing 48823

Abstract

THREE trials were conducted utilizing 192 heifers and 64 steers to evaluate the effects of MGA, DES and the combination of MGA and DES on feedlot performance of cattle.

Heifers fed MGA at 0.35 mg per head daily increased average daily gains for heifers over heifers fed 10 mg DES, heifers implanted with 12 mg plus 24 mg DES or controls, in all three trials. The difference between heifers fed MGA and heifers fed DES was significant (P<.05) only in trial I. In trial III heifers fed MGA, implanted with DES or both, had significantly (P<.05) higher average daily gains than the control heifers. MGA had no significant effect on average daily gain of steers.

Carcass grade, fat thickness at the 12th rib and rib eye area were unaffected by any hormone treatement in the three trials. However, dark cutting carcasses were observed in all three trials. There appeared to be an interaction between hormone treatement and type of ration fed or time of slaughter. It appears that when heifers are fed MGA and/or DES in conjunction with a high corn silage ration, the incidence of dark cutting carcasses will not increase above normal occurrence if they are fed as much as 1% of their body weight daily in grain.

¹ Published with the approval of the Director of Michigan Agricultural Experiment Station as Journal Article No. 5824.

² Melengestrol acetate used in this study supplied by Tuco Products Company, Division of Upjohn Company, Kalamazoo, Michigan.

³ The advice of Dr. William Magee in designing the statistical analyses was greatly appreciated.

⁴ Current address: The Ohio State University, Fremont Area Center, Fremont, Ohio.