Conception failure in swine: importance of the sex ratio of a female's birth litter and tests of other factors.

Failure of gilts and sows to conceive when they are mated is a potentially serious economic cost for swine producers. In Exp. 1, we determined that anogenital distance of newborn gilts is related to the proportion of males in the litter (P < .001). Gilts from litters with more males have larger anogenital distances (mean = 8.0 +/- .2 mm); those from litters with low proportions of males have smaller anogenital distances (mean = 5.7 +/- .1 mm). In Exp. 2, we examined the effect of birth litter sex ratio of sows and gilts on reproductive performance using a 13-yr database of breeding and litter data. Gilts that failed to become pregnant on the first breeding attempt came from litters with significantly higher proportions of males than gilts that successfully conceived on the first breeding attempt. Overall, female swine were significantly more likely to exhibit lower rates of successful breeding during their first four breeding attempts if they had been born in a male-biased litter. These results have implications for swine producers deciding which gilts to keep and which to market. Given the higher probability of reproductive problems for gilts from litters of 12 or more pigs with 67% or more males, these females should likely become market hogs. Sow's age, mode of insemination, and the number of insemination attempts at an estrus period, but not season, can affect successful breeding.