Megestrol acetate for estrus postponement in the bitch.

The postponement of estrus by megestrol acetate (MA) was evaluated in 389 female dogs. MA was administered for 8 days in a daily dose of 2.2 mg/kg body weight beginning in early proestrus. Estrus was suppressed in 357 of these animals (92%). An additional 119 bitches in anestrus received MA in a daily dose of .55 mg/kg body weight for 32 days. Estrus was suppressed in 115 of these animals (97%). Pyometra was observed in 3 of 389 animals (.8%); other adverse affects were minimal. 19 animals received MA in a daily dose of .55 mg/kg body weight for 32 days regardless of the stage of the estrous cycle. 15 of these bitches whelped normal litters after the 1st posttreatment estrus and 4 after mating at the 2nd posttreatment estrus. Litter characteristics were similar to those observed in controls.