Ovulation rate and embryonic migration in cross-bred gilts.

The object of the investigation was to compare the activity between left and right ovaries in gilts slaughtered after their 1st, 2nd, 3rd or 4th detected oestrus and to relate the incidence of embryonic migration to the total number of foetuses present. The study comprised 254 cross bred gilts (Swedish Landrace X Swedish Yorkshire) not returning to oestrus within 24 days after A.I. with frozen semen. The gilts were slaughtered 5-8 weeks after A.I. The genital tracts were examined within two hours after slaughter. The number of corpora lutea and the number of normally developed foetuses were recorded. The results indicated that the left ovary had a higher ovulation rate than the right (P less than 0.001). The left ovary was also heavier than the right (0.01 less than P less than 0.05). The number of corpora lutea increased from oestrous number 2 to 4 (2 vs 4, 3 vs 4, 0.01 less than p less than 0.05). The oestrous number did not significantly influence the fertilization rate. The incidence of embryonic migration increased with increasing number of foetuses (0.01 less than p less than 0.05). Migration from left to right and from right to left occurred with the same frequencies.