Retrospective evaluation of production characteristics in Sinclair miniature swine--44 years later

Three hundred seventy-one litter records collected between 1986 and 1993 from 156 Sinclair S-1 miniature sows, a Hormel-derived strain of miniature swine, were retrospectively analyzed and compared with published records for 1960 to 1962 and 1963 to 1966. The effect of several variables such as season and month of parturition, age of sow, parity, and litter size on reproductive parameters of the Sinclair miniature swine were evaluated. The mean and standard error of the mean for litter size, number of liveborn, number of stillborn, and litter size at weaning of the Sinclair S-1 miniature swine were 7.20 +/- 0.12, 6.67 +/- 0.12, 0.63 +/- 0.06, and 6.76 +/- 0.12 piglets respectively. From a total of 2,436 liveborn piglets, 2,133 (87.56%) were weaned. The litter size at birth was similar to that previously reported for this strain of swine, whereas the litter size at weaning increased (P < 0.001) from 4.7 piglets during 1963 to 1966 to 6.8 piglets in our study. The average birth weight decreased (P < 0.001) from 0.90 kg in 1960 to 1962 and 0.72 kg in 1963 to 1965 to 0.69 kg in our study. Reproductive variables that had a considerable effect on the miniswine reproduction included month of parturition, age of sow, parity, and litter size. Primiparous sows had the smallest litter size and lowest number of weaned piglets. Sows during their second and third parity or sows between 2 and 4 years old had the best reproductive performances. Litter size and number of stillborn increased with parity and age of sow, resulting in fewer piglets weaned in older sows. Litter size had a curvilinear effect on preweaning mortality, with the highest mortality in small and large litters. Overall, production efficiency of the Sinclair miniswine has been stable or has improved since 1960, and all reproductive variables evaluated, except season, were found to have a profound effect on miniswine reproduction.