This study was designed to determine if reduced second-litter size is associated with sow genetics, weaning-to-service interval for primiparous sows, or other covariates thought to influence litter size. A database of 135 herds was analyzed retrospectively using analysis of covariance. Of the 135 herds, 40% had fewer pigs born alive in their second litter thanin the first. A large first-litter size was the major determinant of fewer pigs being born alive in the second litter. Based on least-squares means, 6 out of 13 sow genetic groups had fewer pigs born alive in the second litter than in the first; however, the difference depended on the weaning-to-service interval. A short lactation length and a heavy average weaned pig weight was associated with fewer pigs born alive in the second litter than in the first. In conclusion, delaying the breeding of primiparous Large-White (or Yorkshire) × Landrace sows post-weaning was related to an increased number of pigs born alive in their second litter.