Influence of the Boar and Ejaculation Frequency on Pregnancy Rate and Embryonic Survival in Swine1

Abstract

Semen collected at 24- and 72-hr intervals from 18 Yorkshire boars (avg age 13.5 months) was used to artificially inseminate 177 primi-parous Yorkshire sows. Each sow was inseminated on the second day of standing estrus with 100 ml of diluted semen (egg yolk-citrate-cata-lase extender) containing 2.5 × 109 motile sperm. The sows were slaughtered 25 days after insemination and the reproductive tracts dissected for analyses. Ejaculates collected on the 24-hr schedule had smaller volumes (161 vs 195; P<01), fewer sperm per milliliter (99 vs 221 × 106; P<.01) and fewer sperm per ejaculate (11.2 vs 32.1 × 109; P<01) than ejaculates collected on the 72-hr schedule. The overall pregnancy rate was 76% and sows inseminated with semen collected at 24-hr intervals had a higher pregnancy rate than sows inseminated with semen collected at 72-hr intervals (83 vs 70%; P<.05). The mean corpora lutea number of the 177 sows was 14.2 (SE ± .2) and sows (135) that conceived averaged fewer corpora lutea than sows (42) that returned to estrus (13.5 vs 16.5; P<.025). The pregnant sows had a mean embryo number of 9.9 (SE ± .3) at 25 days of pregnancy, and litter size did not vary significantly between sows inseminated with semen collected at 24- and 72-hr intervals (9.9 vs 10.0). There was a significant quadratic relationship between litter size and ovulation rate. The multiple correlation coefficient between these two variables was .30 (P<.01). Boars varied significantly with respect to the semen characteristics measured, impregnation rate and size of litters they sired. Furthermore, there was a positive correlation (r = .80, P<.01) between the impregnation rate of the boar and the average size of the litters he sired, suggesting that litter size can be effectively increased by culling boars with low impregnation rates.