THE ACCESSORY SPERM COUNT IS RELATED TO EARLY EMBRYONIC DIVERSITY IN PIGS

In pigs, embryonic diversity has been related to embryonic mortality. The relative importance of differences in the duration of ovulation an d in the average accessory sperm count (number of sperm cells in the z ona pellucida) between sows as a cause of differences in within-litter embryonic diversity was studied. Two experiments were performed in wh ich sows were either ovulating spontaneously (Experiment 1; n=13) or w ere induced to ovulate with human chorionic gonadotropin (hCG) (Experi ment 2; n=15). The sows were slaughtered at 98+/-8 and 118+/-2 h after ovulation, respectively, for observation of embryonic diversity. The duration of ovulation varied between 1 and 4 h and was on average 1.8/-0.6 and 2.3+/-0.5 h (P>0.10) for Experiment 1 and 2, respectively. E mbryonic development in terms of the number of cell cycles tended to d iffer between Experiment 1 and 2 (3.5+/-0.8 and 5.6+/-0.5, respectivel y; P<0.10).Within-litter embryonic diversity (SD of number of cell cyc les) was 0.83+/-0.35 and 0.60+/-0.27 (P>0.10), respectively. The avera ge per litter accessory sperm count was variable (ranging from 1 to 75 ) and was affected by experiment (median: 32+/-27 and 12+/-14, respect ively; P<0.05). Within-litter embryonic diversity was not related lo t he duration of ovulation (P>0.10) but was negatively related to the av erage or median accessory sperm count (P<0.025). The significant relat ionship between the accessory sperm count and embryonic diversity sugg ests that the duration of fertilization is a determinant for embryonic diversity.