Control of sexual activity in ranch cows by intramuscular and intravaginal administration of progestagens.

Abstract

The results of 2 trials examining the effects of 3 progestagens chlormadinone acetate (CAP) melengestrol acetate (MGA) and megestrol acetate (MA) on the sexual activities of ranch cows are reported. Cows of indigenous breeds had sexual and ovarian activities recorded for 30 months preceding the trials. Ovaries were palpated per rectum at weekly intervals. In the first trail injection of CAP 6 mg a day inhibited manifestation of estrus in 10 of 10 cows while 6 of these cows showed full heat 4-6 days after cessation of treatment. When CAP was administed by intravaginal tampon 200 mg per tampon 8 of 10 cows showed full heat during the 18 days of treatment and 2 showed full heat in the 7 days after cessation of treatment. Trial 2 had 6 groups of 10. CAP was injected 6 mg a day for 16 days and at 12 mg a day on alternated days for 16 days. MGA was injected .5 mg a day for 16 days or administered 60 mg per tampon for 16 days. MA was injected 4 mg each day or administered 100 mg per tampon again for 16 days. With the exception of 1 cow receiving MA injection all progestagens completely inhibited manifestations when injected. In the tampon trials 2 of 10 cows receiving MGA and 2 of 10 receiving MA showed estrus during treatment. During Days 5-10 following treatment heat was shown by 100% of cows receiving CAP injections 80% of those receiving CAP on alternate days and 70% of those receiving MGA or MA. The high incidence of anovulatory heats 20-80% indicated that the first heat after cessation of progestagen treatment would be associated with low fertility. In these studies between 10% and 50% of tampons were ejected prematurely. 60 mg of MGA applied intravaginally resulted in a small amount of vaginal discharge. 200 mg CAP resulted in a copious amount of foul-smelling mucus in the vagina.