Reduced superovulatory response in the ewe following repeated gonadotrophin treatment

Thirty-nine pure bred Texel ewes were superovulated with horse anterior pituitary extract (HAP) and 24 of these ewes were treated for superovulation a second time 55 to 76 days after the first treatment. A 12 day SC-9880 sponge was used to synchronise oestrus in the ewes and all were superovulated with 200 mg HAP (4 days X 50 mg HAP). Surgical insemination and cervical insemination were employed to breed the ewes following the first and second superovulation treatments, respectively. The incidence of oestrus and ewes ovulating were significantly (P less than 0.005) lower following the second treatment. There was no significant difference in the ovulation rate in ewes ovulating between the first and second treatments. The mean number of eggs recovered per ewe decreased following the second treatment but fertilisation rate was not affected. Results would suggest that the period of time between first and second superovulation treatments was not sufficiently long to allow Texel ewes to respond to a second stimulation, or that surgical insemination may have had a detrimental effect.