Clinical, morphologic, and clinicopathologic findings in Beagles treated for two years with melengestrol acetate

Melengestrol acetate (MGA) was administered orally to groups of 10 female and 3 male Beagles at doses of 0, 1, 2, or 8 microgram/kg of body weight/day for 2 years. Treatment was continuous at the same dose rate in the first 3 groups, but in the 4th group, the dose for bitches was reduced to 4 microgram of MGA/kg/day during the 2nd year. Matings were made within MGA-dosage groups and among 10 additional bitches treated at 1 microgram of MGA/kg/day and the dogs treated at 8 microgram/kg/day. Doses of 8 and 4 microgram of MGS/kg caused progestational effects on the uterus resulting in expected histopathologic changes, dystocia, and pyometritis. Leukocytosis, normocytic, hypochromic anemia, and increased alkaline phosphatase values were the results of systemic and uterine effects consistent with the indirect and expected pharmacologic action of progestational agents in the bitch. Doses of 1 and 2 microgram of MGA/kg in dogs and bitches and 8 microgram/kg in dogs produced no significant differences in clinical observations, hematologic findings, blood chemical analysis, urinalysis, organ weights, or gross and microscopic observations at necropsy.