Effects of a second insemination after ovulation on fertilization rate and accessory sperm count in sows.

Insemination immediately after ovulation causes low fertilization results owing to a low fertilization rate and possibly also owing to polyspermic fertilization. The present experiment was undertaken to study the effects of a second insemination after ovulation on fertilization rate and embryonic development. In multiparous crossbred sows, transrectal ultrasonography was used at intervals of 4 h to determine ovulation. All sows (n = 91) were artificially inseminated with 3 x 10(9) mixed spermatozoa and, in 31 sows, a second insemination took place at 3 +/- 1 (mean +/- SD) h after ovulation. At 119 +/- 5 h after ovulation, the percentage of normal embryos and the accessory sperm count were determined. In the sows that were inseminated once, the percentage of normal embryos decreased when insemination took place more than 24 h before ovulation, from 88 +/- 20% (16-24 h; n = 15) to 63 +/- 40% (24-32 h; n = 10) (P < 0.05). In the sows that were inseminated again after ovulation, the percentage of normal embryos was high, irrespective of the period between first insemination and ovulation. The difference in percentage of normal embryos between the sows that were inseminated once or twice was significant when the first insemination took place between 24 and 32 h before ovulation; 63 +/- 40% (inseminated once, n = 10) and 97 +/- 5% (inseminated twice, n = 8) (P < 0.05). The accessory sperm count of the normal embryos in a litter was positively related to the percentage of normal embryos in a litter, and this relation was not affected by the interval between first insemination and ovulation or by the number of inseminations.(ABSTRACT TRUNCATED AT 250 WORDS)