Intra-uterine insemination with low numbers of frozen-thawed boar spermatozoa in spontaneous and induced ovulating sows under field conditions

The present study was conducted to evaluate non-return rate (NR), farrowing rate (FR), and number of total pigs born/litter (TB) of weaned sows after intra-uterine insemination (IUI) using low numbers of frozen-thawed (FT) spermatozoa. Semen from 6 boars was cryopreserved individually in a 0.5-ml straw, at a concentration of 1×10⁹ spermatozoa/ml. A total of 40 multiparous sows with weaning-to-estrus interval of 3 to 7days were included. The sows were detected for standing estrus twice daily and randomly assigned to two groups: I) spontaneous ovulation (n =20) and II) induced ovulation (n =20) which the sows were given 750IU human chorionic gonadotrophin (hCG) i.m. immediately at estrus detection. Ovulation was determined every 12h using transrectal ultrasonography. FT semen containing 1×10⁹ motile spermatozoa/dose was used to IUI. In group I, the sows were inseminated at 24h after the detection of estrus and repeated every 12h until ovulation. In group II, the sows were inseminated at 36, 42 and/or 48h after hCG treatment. The results showed that the interval from standing estrus to ovulation (EOI) differed significantly between group I (40.2h) and group II (35.6h; P =0.01). Variation of EOI among sows within each group seemed to be lower in group II (4.5h SD) than in group I (5.5h SD; P =0.5). The number of IUI per sow was 2.9±0.6 times in group I and was 2.4±0.5 times in group II. There were no significant differences (P >0.05) in the NR (80 vs 85%), FR (60 vs 65%) and the TB (8.0±2.8 vs 9.4±3.7 piglets/litter) between the groups. These results indicated that multiple doses of IUI with a low number of FT boar spermatozoa provided a fairly good NR, and reasonable FR and TB both in spontaneous and induced ovulating sows. The number of inseminations required for attaining acceptable fertility tended to be lower in the weaned sows with induced ovulation.