EFFECTS OF TIME OF INSEMINATION RELATIVE TO OVULATION, AS DETERMINED BY ULTRASONOGRAPHY, ON FERTILIZATION RATE AND ACCESSORY SPERM COUNT INSOWS

The effects of the timing of insemination relative to ovulation on fer tilization rate, accessory sperm count and early embryo development we re studied in sows. Oestrus detection was performed at intervals of 8 h. Sows were artificially inseminated once with 3 x 10(9) spermatozoa. Transrectal ultrasonography was performed at intervals of 4 h to dete rmine when ovulation occurred and sows were killed at 120 +/- 6 h afte r ovulation. For each insemination-ovulation interval of 8 h, fertiliz ation rates were as follows: > 48 h, 35% (n = 1); 48-40 h, 51 +/- 36% (n = 6); 40-32 h, 54 +/- 36% (n = 14); 32-24 h, 79 +/- 32% (n = 19); 2 4-16 h, 94 +/- 11% (n = 24); 16-8 h, 92 +/- 21% (n = 24); 8-0 h, 95 +/ - 22% (n = 21) and for the sows that were inseminated after ovulation: 0 to - 8 h, 75 +/- 38% (n = 26); - 8 to - 16 h, 74 +/- 43% (n = 15) a nd < - 16 h, 0% (n = 1). The median accessory sperm count differed amo ng the groups from 1. (insemination 40-48 h 1 before ovulation) to 126 (insemination 0-8 h after ovulation) (P = 0.0001). Within each 8 h ti me interval, the normal embryos from sows with less than 90% normal em bryos were less developed and had a lower sperm count than did the nor mal embryos from sows with more than 90% normal embryos (P < 0.05). In conclusion, fertilization rate and the accessory sperm count of the n ormal embryos were dependent on the interval between insemination and ovulation; fertilization results were optimal when insemination took p lace between 0 and 24 h before ovulation. Partial fertilization occurr ed in all the insemination-ovulation time intervals, but the frequency differed among the time intervals. In every insemination-ovulation ti me interval of 8 h the between-sow variation of reproductive character istics (fertilization rate, accessory sperm count, embryo development) was large. The reasons for this variability between sows are unclear.