EFFECTS OF A 2ND INSEMINATION AFTER OVULATION ON FERTILIZATION RATE AND ACCESSORY SPERM COUNT IN SOWS

Insemination immediately after ovulation causes low fertilization resu lts owing to a low fertilization rate and possibly also owing to polys permic fertilization. The present experiment was undertaken to study t he effects of a second insemination alter ovulation on fertilization r ate and embryonic development. In multiparous crossbred sows, transrec tal ultrasonography was used at intervals of 4 h to determine ovulatio n. All sows (n = 91) were artificially inseminated with 3 x 10(9) mixe d 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 de termined. In the sows that were inseminated once, the percentage of no rmal embryos decreased when insemination took place more than 24 h bef ore 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 o vulation, the percentage of normal embryos was high, irrespective of t he period between first insemination and ovulation. The difference in percentage of normal embryos between the sows that were inseminated on ce or twice was significant when the first insemination took place bet ween 24 and 32 h before ovulation; 63 +/- 40% (inseminated once, n = 1 0) and 97 +/- 5% (inseminated twice, n = 8) (P < 0.05). The accessory sperm count of the normal embryos in a litter was positively related t o 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. On the basis of the high percentage of normal embryos in sows that were inseminated twice and the positiv e relation between the accessory sperm count and the percentage of nor mal embryos, it is concluded that under these experimental conditions, fertilization results were affected positively by a second inseminati on after ovulation.