Feedlot performance and pregnancy inhibition of heifers treated with depot-formulated melengestrol acetate.
In dose titration trials beef heifers received depot-formulated melengestrol acetate (DEPO-MGA) in single s.c. ear injections to determine effects on performance and pregnancy inhibition. In a 112-d feedlot trial, 105 heifers were assigned to light, medium and heavy weight blocks on five treatments: dietary MGA (.5 mg.hd-1.d-1), control (no MGA) or DEPO-MGA on d 1 at .5, 1.0 or 1.5 ml/hd (30, 60 or 90 mg MGA/hd, respectively). A high-energy cracked corn diet was fed to all heifers ad libitum. At d 56 and d 112, ADG and feed/gain were not affected (P greater than .05) by dietary MGA or DEPO-MGA treatments, although dietary MGA tended to increase 112-d ADG (1.67 vs 1.58 kg) compared with controls. In a pasture trial, 100 beef heifers were assigned by weight to five treatments: control (no MGA) or DEPO-MGA injected on d 1 at .5, 1.0, 1.5 or 2.0 ml/hd (30, 60, 90 or 120 mg MGA/hd, respectively). Heifers were pastured as a single herd and were exposed to fertile bulls from d 7 to d 181. Weights and pregnancy data were recorded at d 62, 90, 134, 181 and 225. Heifer ADG was not affected (P greater than .05) by DEPO-MGA treatment at any weighing date. By d 90, 90% of control heifers were pregnant, and 100% were pregnant by d 134. Pregnancy inhibition rates of 90% to 100% for each DEPO-MGA treatment at d 62, 90 and 134 were higher (P less than .01) than those in control heifers. Pregnancy was inhibited in 90% of heifers on 60-mg and 90-mg DEPO-MGA treatments through d 181, and in 95% of heifers on the 120 mg DEPO-MGA treatment through d 225.
Hill
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GM
University of Georgia, Tifton 31793-0748.
Richardson
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Utley
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D000818:Animals; D001835:Body Weight / Q000187:drug effects*; D002417:Cattle / Q000254:growth & development*; D003271:Contraceptive Agents, Female / Q000008:administration & dosage / Q000494:pharmacology*; D003692:Delayed-Action Preparations; D005260:Female; D007279:Injections, Subcutaneous; D008552:Melengestrol Acetate / Q000008:administration & dosage / Q000494:pharmacology*; D011245:Pregnadienes / Q000494:pharmacology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000187:drug effects*
D003271:Contraceptive Agents, Female; D003692:Delayed-Action Preparations; D011245:Pregnadienes; D008552:Melengestrol Acetate