Improvement of fertility in post-partum beef cows by treatment with PMSG and progestagen

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Abstract
In group 1, progesterone (3.0 g)-impregnated intravaginal sponges were inserted into 142 cows for 9 days. On the day of insertion an i.m. injection of 250 mg progesterone + 7.5 mg estradiol benzoate was given. In group 2, Cronolone (0.2 g [flurogestone acetate])-impregnated intravaginal sponges were inserted into 120 cows for 9 days and an i.m. injection of 20 mg Cronolone + 7.5 mg estradiol benzoate was given on the day of sponge insertion. Approximately half of the cows in each group received 750 IU PMSG [pregnant mare''s serum gonadotropin] (Intervet) i.m. at the time of sponge removal. The high incidence of twin births among cows treated after 60 days post partum suggests that the endocrinological state of these animals is similar to that of cyclic cows and that PMSG given at this time results in an increased ovulation rate by augmenting the endogenous FSH [follicle-stimulating hormone] concentrations. The gonadotrophin administration in conjunction with a short-term progestagen treatment apparently is an effective method of inducing ovulation in these animals.