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, requiring informed consent of the owners. The queen should be allowed an estrus before resuming therapy. Mibolerone is also not approved for use in queens (due to hepatotoxicity) but is effective at 50 μg/cat, PO, sid. Longterm deslorelin implants have also suppressed estrus in cats, but the length of suppression is variable. Estrus may be induced in queens with FSH, 2 mg, IM, the first day, then 0.5–1 mg, IM, daily for 4 additional days. Recommended doses of 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 μg, IM. Ovulation is reported to occur 25–27 hr after hCG administration to queens.
Last full review/revision July 2011 by Steven P. Brinsko, DVM, MS, PhD, DACT