Ovulation and embryonic developmental rate following hCG-stimulation in sows

The hCG induced ovulation in sows was studied by use of ultrasonography, and an investigation of the development and diversity of the zygotes/embryos was performed at 24 h after ovulation. Crossbred sows (N = 48) were weaned (day 0) and checked for heat twice daily from day 3 onwards. From day 4, the ovaries were transrectally scanned twice daily. On day 4, the sows were given an injection of 750 iu hCG i.m. and inseminated 27 +/- 2 h (X +/- SD) and 38 +/- 1 h later. From 38 to 48 h after the hCG injection, the ovaries were scanned at 60 to 90 min intervals. At 24 h after ovulation the oviducts were surgically flushed in 18 sows. Out of the 48 sows, 34 showed heat at 12-36 h after the hCG-treatment and 14 showed heat before the hCG treatment. In the former group of sows, 20 (59%) ovulated within the interval of 38 to 48 h after the hCG treatment, and the follicular size immediately before ovulation was 7.8 +/- 0.6 mm. Among the sows which showed heat before hCG treatment only 7 (50%) ovulated within the above interval and the preovulatory follicle size was larger (8.3 +/- 0.5, p < 0.05) than in the former group of sows, which showed heat after the hCG treatment. The flushing of 18 sows yielded a total of 243 ova, 70 (29%) 1-cell stages, 160 (66%) 2-cell stages and 13 (5%) 4-cell stages. A pronounced difference in the degree of variation in embryonic development was seen between sows: 4 animals yielded 1- to 4-cell stages, one exclusively 2-cell stage. In conclusion, the control of ovulation in sows by hCG treatment will affect the follicular growth and the exact timing of ovulation can not always be relied on. It is strongly recommended to use ultrasonography to monitor the time of ovulation if this parameter is important. Ova recovered at 24 +/- 1 h after the median time of ovulation revealed a pronounced diversity (1- to 4-cell stage) within sows. No obvious relation with this embryonic diversity and the follicular size at ovulation was seen in these data.