Synovex-H has consistently stimulated daily gain and improved feed efficiency of feedlot heifers. However, this hormone does not inhibit the estrus cycle in heifers (which is responsible for excessive animal activity restricting feedlot performance during periods of hot weather). Melengestrol acetate (MGA), a new, synthetic high-potency hormone compound had previously been reported to increase feeding performance when added to the daily ration—and in the two tests reported here, also effectively controlled estrus. Both MGA and Synovex-H significantly increased daily gain and improved feed efficiency over the control animals. The MGA-fed heifers shrank less in transit than either the Synovex-H or control groups, although dressing percentage was about the same for all groups. Tenderness and fat content of rib and bottom round steak were not affected. The size of the rib eye from the MGA-fed heifers was slightly smaller than from the control or Synovex-H groups.

Assistance in conducting these tests was obtained from: Upjohn Company, Kalamazoo, Michigan; Cattle Feeders of Palo Verde Valley and Alpha Beta Packing Co. of Huntington Beach; and from Dr. George Crenshaw, Extension Animal Health Specialist, and Cheryl Waul, Department of Food Science and Technology, University of California, Davis.