Factors influencing the proportion of offspring from a second insemination in sows

Sows (n = 367) showing standing heat between days 4 and 6 after weaning were inseminated twice with a 24 h interval. To distinguish offspring, Great Yorkshire (GY) semen was used for the first insemination (ins1) and Meishan (MEI) semen for second (ins2), or in reverse order. Factors influencing the number of piglets born from ins2 were: weaning to oestrus interval (WOI, P < 0.001), genotype of the sow (P < 0.05), parity (P < 0.10) and the interaction between treatment and MEI boar (MEI for ins1 or for ins2, P < 0.001). The distribution of litters after litter type (1, completely from ins1; 2, mixed litters; 3, completely from ins2) was dependent on: WOI (P < 0.001), genotype (P < 0.05) and the interaction between treatment and MEI boar (P < 0.001). The interaction between treatment and MEI boar was due to one of the MEI boars that produced lower numbers of offspring compared with the other boars. The number of offspring from ins2, 24 h later, was higher when ins1 was performed with semen of this MEI boar (P < 0.05). The number of offspring from ins1, 24 h earlier, was higher when ins2 was performed with semen of this boar (P < 0.05). concluded that the second insemination, 24 h after the first, did contribute to the offspring and that the level of this contribution was dependent on the factors WOI, genotype of the sow, parity and boar.