The effects of the timing of insemination relative to ovulation on fertilization rate, accessory sperm count and early embryo development were studied in sows. Oestrus detection was performed at intervals of 8 h. Sows were artificially inseminated once with 3 \m=x\109 spermatozoa. Transrectal ultrasonography was performed at intervals of 4 h to determine when ovulation occurred and sows were killed at 120 \ m=+-\ 6 h after ovulation. For each insemination\p=n-\ovulation interval of 8 h,

more »

... ation rates were as follows: > 48 h, 35% (n = 1); 48\p=n-\40 h, 51 \ m=+-\ 36% (n = 6); 40\p=n-\32h, 54 \ m=+-\ 36% (n = 14); 32\p=n-\24h, 79 \ m=+-\ 32% (n = 19); 24\p=n-\16h, 94 \ m=+-\ 11% (n = 24); 16\p=n-\8h, 92 \ m=+-\ 21% (n = 24); 8\p=n-\0h, 95 \ m=+-\ 22% (n = 21) and for the sows that were inseminated after ovulation: 0 to \ m=-\8 h, 75 \ m=+-\ 38% (n = 26); \ m=-\8 to \m=-\ 16 h, 74 \ m=+-\ 43% (n = 15) and < \m=-\16 h, 0% (n = 1). The median accessory sperm count differed among the groups from 1 (insemination 40\p=n-\48h before ovulation) to 126 (insemination 0\p=n-\8 h after ovulation) (P = 0.0001). Within each 8 h time interval, the normal embryos from sows with less than 90% normal embryos were less developed and had a lower sperm count than did the normal embryos from sows with more than 90% normal embryos (P < 0.05). In conclusion, fertilization rate and the accessory sperm count of the normal embryos were dependent on the interval between insemination and ovulation; fertilization results were optimal when insemination took place between 0 and 24 h before ovulation. Partial fertilization occurred in all the insemination\p=n-\ovulationtime intervals, but the frequency differed among the time intervals. In every insemination\p=n-\ovulationtime interval of 8 h the between-sow variation of reproductive characteristics (fertilization rate, accessory sperm count, embryo development) was large. The reasons for this variability between sows are unclear.