An Appraisal of Factors Affecting Prolificacy in Swine1

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Abstract
The effects of age and inbreeding of the dam, and inbreeding of the litter on litter size were studied from intra line, intra year simple and partial regressions calculated from the records of 749 inbred Poland China and Minnesota No. 1 gilts farrowing for the first time at approximately one year. The relative effects of age, weight at breeding, gains made during pregnancy, and body length were determined from the data on 508 of the gilts. Litter size increased with an increase in the age of the dam at farrowing. The effect of age was much greater during the period prior to 12 months than later. Gilts farrowing at 320 days averaged 1 pig less, and those farrowing at 410 days about one half pig more than those at one year. Litter size decreased with an increase in the inbreeding of the dam but apparently was unaffected by the inbreeding of the litter. An increase of ten percent in the inbreeding of dams of the same age resulted in a decrease of about 0.6 pigs per litter. Copyright © . .