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Estrus Synchronization in Cattle Following Feeding Six Progestogens¹

Department of Animal Sciences, New Jersey Agricultural Experiment Station, Sussex

ABSTRACT

The oral effectiveness of six progestogens in synchronizing estrus was determined in dairy heifers. The hormones were fed in a concentrate ration twice daily for 17 or 18 days. Four progestogens effectively synchronized estrous cycles at the levels studied. Progestogen 1 (6-methyl-4-pregnen-17-Ol-one acetate) synchronized estrus at minimum effective levels of 80 and 90 mg daily. Fertility at the synehronized estrus after Progestogen 1 feeding was depressed, as only 24.1% of the heifers conceived compared with conception in 48.5% of the controls at first service. After two services the conception rates were 65.5 and 69.7% for treated and control heifers, respectively. Progestogen 2 (6-methyl-3,5-pregnadien-17 -Ol-20-one-3-ß-acetylthioethoxy acetate) was effective in controlling the estrous cycle at 30 mg daily. Increased levels of this compound up to 90 mg daily did not increase the interval to estrus after the end of treatment. The minimum effective doses of Progestogen 3 (3-aza-A-homo-6-methyl-4-pregnen-17-Ol-4-one acetate) and Progestogen 4(6-methyl-4-pregnen-17-Ol-3,20-dione-3-ethylene thioketal acetate) were 45 and 90 mg daily. Progestogen 5 (6--methyl-4-pregnen-17-Ol-3,20-dione-3-oxime acetate) and Progestogen 6 (17-ethynyl-19-norandrost-4,6-diene-3-one-17ß-acetate 3-oxime) were ineffective in controlling estrous cycles at the highest levels tested (90 mg).

¹ Paper of the Journal Series, New Jersey Agricultural Experiment Station. This investigation was supported in part by funds provided by Johnson and Johnson Company, New Brunswick, New Jersey.

² Present address: Center for Research in Reproductive Biology, Department of Obstetrics and Gynecology, University of Michigan Medical Center, Ann Arbor.