The effect of superovulation on fertilisation and embryonic survival in the pig

Abstract

1. Thirty-one gilts were injected subcutaneously with 1,500 i.u. PMS on Day 15 of the cycle, and inseminated on the morning of the 2nd day of oestrus.2. Twenty of the animals were killed 1 to 4 days after insemination to study fertilisation, and the remaining eleven were killed on the 25th day of pregnancy to study embryonic survival.3. All animals exhibited normal oestrous behaviour, only two of them failing to return to oestrus by Day 19 of the cycle. Treatment with PMS shortened the follicular phase of the cycle in nearly all instances.4. Eighteen of the twenty animals in which eggs were studied were fertile and within these 84·2% of the eggs examined were undergoing normal development, 2·1% were fragmenting, 4·0% were polyspermic and 7·8% were primary oocytes. Ten unpenetrated secondary oocytes (1·9%) were also recovered.5. Of the eleven animals in which embryonic survival was studied, only eight were pregnant at autopsy; the remaining three had 35 to 44 corpora albicantia, but no embryonic remains could be detected in the uterus.6. The average ovulation rate in the eight pregnant animals was 35·4, with a range of 13 to 48. However, the average number of normal embryos was 17·0, with a range of 7 to 28.7. The percentage survival of normal embryos varied from 26% to 83%. Embryonic survival was better at ovulation rates below that of the mean (35·4); an abnormally large or complete loss of embryos occurred at ovulation rates higher than 36.8. Despite the range in percentage survival, the number of normal embryos found at the 25th day of pregnancy in five of the gilts was considerably above that found in untreated gilts.