The effect of GnRH analogue (buserelin) treatment on day 12 post mating on ovarian structure and plasma progesterone and oestradiol concentration in ewes

An investigation was conducted into the effect of buserelin treatment on day 12 post mating on ovarian function and plasma progesterone and oestradiol-17 beta concentration in ewes. Changes in ovarian structures were determined, at laparoscopy or after slaughter, 48 h after treatment in 38 control and 41 ewes given an injection of 4 mu g buserelin on day 12 post mating (day 0=day of oestrus). Ovulation rate was higher in buserelin treated (2.76) than in control (1.87) ewes (P <0.05). Moreover, 41 of the 113 corpora lutea observed in the buserelin group were the result of ovulations that had occurred within 48 h post treatment, compared with two of 71 in the controls (P <0.05). Blood samples were collected from 10 ewes in each treatment group for hormone analysis. Mean progesterone concentrations tended to be higher, in samples collected from 2 to 6 h post treatment, in the buserelin group (4.31 (s.e. 1.32) mu g/l) compared with the control group (3.71 (s.e. 1.44) mu g/l. Furthermore, overall mean oestradiol concentrations were lower, during days 13, 14 and 15 post mating, in buserelin treated (0.72 (s.e. 0.26) ng/l) than in control (0.94 (s.e. 0.50) ng/l) ewes (P <0.05). The results of this study indicate that buserelin treatment on day 22 post mating changes ovarian function.