J. Anim Sci.
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J. Anim Sci. 1971. 32:179-184.
© 1971 American Society of Animal Science
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Genetic Analysis of a Swine Control Population. I. Population Stability1

Ronnie L. Edwards2, I. T. Omtvedt and J. A. Whatley

Oklahoma Agricultural Experiment Station, Stillwater 74074

Abstract

A zero-selection control herd was established in the Oklahoma swine breeding project in 1961 to evaluate season and age of dam influences on performance. The purpose of this study was to evaluate the effectiveness of this population as a genetic control. The data included records on 3,860 pigs born in 363 litters from 1962 to 1968. To minimize inbreeding, one boar was used per gilt and no matings were permitted when a common ancestor appeared in the first two generations of the pedigree. From the 25 to 30 litters farrowed each season, approximately 10 sows were randomly selected for a second litter and repeat mated to the same boar to evaluate age of dam effect. Two average boars and two average gilts from each litter were selected prior to weaning and then the boar and gilt from each pair that was nearest to the average for postweaning daily gain and probe backfat thickness was retained to propagate the line. Average selection differentials for female replacements were 0.017 kg for daily gain and -.005 cm for probe backfat. The regressions of performance on time were nonsignificant for the traits evaluated. Confidence intervals calculated for the adjusted season means or number of pigs per litter at birth, 21 and 42 days and litter weight at birth, 21 and 42 days indicated no major shifts in the population over the 14 seasons studied. Although the analyses employed were approximate methods which would require rather marked instability to be detected using these analytical procedures with the limited data available, it was concluded that this population remained relatively uniform in performance since its foundation and could serve as an effective control population. The average population inbreeding at the end of the study was 1.4% with individual inbreedings ranging from zero to 2.7%. Sows had larger litters of heavier pigs at birth, 21 and 42 days in their second litters than in their first litters. Gilts farrowing in March and April had more pigs per litter at birth, 21 and 42 days than gilts farrowing in September and October. However, sows farrowing in the spring farrowed fewer pigs but raised a higher proportion to weaning than sows farrowing in the fall.

Footnotes

1 Approved as Journal Manuscript No. 1958 of the Oklahoma Agricultural Experiment Station. Project 808 in cooperation with Regional Swine Breeding Laboratory, U.S.D.A., A.R.S., A.S.R.D.

2 Present address: Extension Swine Specialist, Bowling Green, Kentucky.






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Copyright © 1971 by the American Society of Animal Science.