Effects of melengestrol acetate on reproduction in the Beagle bitch.

Melengestrol acetate orally given to bitches at dose levels of 200 mug or more each day effectively inhibited estrous activity for a treatment period of 243 days and a lapsed period of more than 400 days from the preceding estrous period. The 100-mug dose of the drug, given orally once a day, starting immediately after the bitches were bred or late in gestation, had no effect on conception, pregnancy, or parturition. Gestation was prolonged in bitches given melengestrol acetate starting 1 day after breeding. Drug-polymeric implants blocked reproductive activity, and the progestogen induced cystic endometrial hyperplasia.