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Hormonal Control of Estrus in Cats

By Juan E. Romano, DVM, MS, PhD, DACT, College of Veterinary Medicine, Texas A&M University

Megestrol acetate may be used to suppress estrus in queens by treating with 5 mg/cat daily for 3 days, then 2.5–5 mg once weekly for a maximum of 10 wk. Administration of megestrol acetate to queens is an extra-label use of the drug, and informed consent should be obtained from the owners. The queen should be allowed an estrus before resuming therapy. Mibolerone is also not approved for use in queens (because of hepatotoxicity) but is effective at 50 mcg/cat/day, PO. Longterm deslorelin implants have also suppressed estrus in cats, but the length of suppression is variable. Estrus may be induced in queens with follicle-stimulating hormone (FSH), 2 mg, IM, the first day, then 0.5–1 mg, IM, daily for 4 additional days. Recommended doses of human chorionic gonadotropin (hCG) range from 25 to 500 IU. The higher doses are more effective at inducing ovulation but may also result in oocyte degeneration. For queens with anovulation or for queens undergoing artificial insemination, ovulation of mature follicles (present on day 2 of estrus) may be induced by treatment with hCG at 250 IU, IM, or GnRH at 25 mcg, IM. Ovulation is reported to occur 25–27 hr after hCG administration to queens.