RETROSPECTIVE EVALUATION OF PRODUCTION CHARACTERISTICS IN SINCLAIR MINIATURE SWINE - 44 YEARS LATER

Three hundred seventy-one litter records collected between 1985 and 19 93 from 156 Sinclair S-l miniature sows, a Hormel-derived strain of mi niature swine, were retrospectively analyzed and compared with publish ed records for 1950 to 1952 and 1963 to 1965. The effect of several va riables such as season and month of parturition, age of sow, parity, a nd litter size on reproductive parameters of the Sinclair miniature sw ine were evaluated. The mean and standard error of the mean for litter size, number of liveborn, number of stillborn, and litter size at wea ning of the Sinclair S-1 miniature swine were 7.20 +/- 0.12, 6.57 +/- 0.12, 0.63 +/- 0.06, and 5.75 +/- 0.12 piglets respectively. From a to tal 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) fro m 4.7 piglets during 1963 to 1965 to 5.8 piglets in our study. The ave rage birth weight decreased (P < 0.001) from 0.90 kg in 1950 to 1952 a nd 0.72 kg in 1963 to 1965 to 0.59 kg in our study. Reproductive varia bles that had a considerable effect on the miniswine reproduction incl uded month of parturition, age of sow, parity, and litter size. Primip arous sows had the smallest litter size and lowest number of weaned pi glets. Sows during their second and third parity or sows between 2 and 4 years old had the best reproductive performances. Litter size and n umber of stillborn increased with parity and age of sow, resulting in fewer piglets weaned in older sows. Litter size had a curvilinear effe ct on preweaning mortality, with the highest mortality in small and la rge litters. Overall, production efficiency of the Sinclair miniswine has been stable or has improved since 1950, and all reproductive varia bles evaluated, except season, were found to have a profound effect on miniswine reproduction.