Ovarian and hormonal responses of cows to treatment with an analogue of gonadotrophin releasing hormone and prostaglandin F-2 alpha

Blood samples were taken from 11 cows and their ovaries were scanned by ult rasound at least daily. Around day 5 of an induced cycle, they were injecte d with 10 pg buserelin, an analogue of gonadotrophin releasing hormone, and on day 12 they received 0.5 mg cloprostenol, an analogue of prostaglandin F-2 alpha (PCF2 alpha) Two days later six of the cows (the treated group) r eceived a second injection of 10 pig buserelin, but the remaining five rece ived no further treatment (control group). The dominant, that is, the large st follicle in each cow disappeared after the first buserelin injection and was replaced by a new one which grew synchronously in all the cows until a fter the treatment with PCF2 alpha Ovulation occurred significantly earlier after PCF2 alpha in the treated group than in the control group (72 to 96 hours v 96 to 120 hours; P<0.05). Plasma progesterone concentrations then i ncreased more rapidly in the treated group than in the control group and we re significantly higher on days 5 and 4 after ovulatson (P<0.05).