Multiple mating and paternity determinations in domestic swine (Sus scrofa)

When a sow copulates with different boars, fecundation can take a slant towards the best quality male, which should have a more competitive ejaculation. In polyandric animals, genitals can be more elaborated and be an indication of spermatic competence or cryptic female choice. In swine, the male and female genital morphologic characteristics are evidence that allow the assumption of spermatic competence and cryptic choice in this species. In order to prove this hypothesis, the paternity of a group of 18 York/Landrace (Y/N) sows was determined; these sows copulated with three boars: Yorkshire (Y/Y), York/Landrace (Y/N) and Landrace (N/N). The three boars had the same probability of copulating in the first, second, and third place with each of the sows in an interval of 12 hours between each mating. Four polymorphic molecular markers were used in order to establish the paternity (S0033, S0035, S0036 and S0037). The results indicate that the Y/N male had 85.59% of paternity, Y/Y male 8.8% and N/N 5.8%. According to the mating order, when the Y/N male copulated in the first place, it had 89.6% paternity (26 offspring; 12 males; 46.15% and 14 females, 53.85%) when it copulated in the second place, it had 100% paternity (8 offspring; 4 males, 50% and 4 females, 50%), and when it mated in the third place, it had 77.41% paternity (22 offspring; 13 males, 59.1% and 9 females, 40.9%). Sows in estrus participated in the removal of semen from four sows minutes after the copula by female-female mating. The multiple mating allowed certain competence among the ejaculation and the possibility of the female to slant the paternity towards the heterozygote male with higher genetic variability, compared to the homozygote male (Y/Y and N/N).