Because of much interest in multiple births of calves, there is a need to investigate the problems associated with gestation of two to four embryos. This paper relates number of cl to plasma progesterone concentrations in maiden cows of beef breeds.
In Exp. 1, carried out in September 1969, oestrous cycles of eighteen Angus and Hereford cows, 18 to 20 months old, were suppressed with 0·5 mg melengestrol acetate (MGA—The Upjohn Co., Kalamazoo)/cow/day for 18 days. Four days before the end of MGA treatment, 1500 to 3000 i.u. pmsg were given to induce multiple ovulation. The cows were fasted for 3 days after the pmsg injection to reduce excessive follicular development (Lamond, 1970). Thirteen cows which came into oestrus on the 3rd day after cessation of hormonal treatments were