The effect of two different levels of progesterone priming on the response of ewes to superovulation

The use of either 1 or 3 controlled internal drug release (CIDR) devices for progesterone priming in ewes (n=11) superovulated with 1500 IU pregnant mare serum gonadotrophin (PMSG) at 28 hours prior to CIDR device withdrawal was investigated in relation to the stages of development and viability of the ova produced. Progesterone levels in the ewes (n=6) treated with 3 CIDR devices were significantly higher (P<0.01) during the 11 days of insertion than in those (n=5) treated with 1 CIDR device (7.3 vs 3.3 ng/ml) over the same period. However, following superovulation, the mean (+/-SEM) ovulation rates were similar for both groups (8.2 +/- 1.7 vs 10.2 +/- 1.5). The number of ova (M+/-SEM) recovered by laparoscopy 5 days after insemination was 4.2 +/- 1.0 for ewes treated with 3 CIDR devices and 7.0 +/- 1.1 for those treated with 1 CIDR device (P<0.10). The respective ovum recovery rates (M+/-SEM) were 55+/-9.8 and 74+/-13.2%. There was no effect of progesterone concentration in the priming phase on either the stages of development of the recovered ova or on their ability to develop during in vitro culture. It was concluded, therefore, that progesterone concentrations within the range 3.3 +/- 0.1 to 7.3 +/- 0.3 ng/ml during the priming phase and 2.4 +/- 0.3 to 6.5 +/- 0.2 ng/ml at the time of PMSG administration did not affect the ovulation rate or the viability of ova recovered from superovulated ewes.