Swine Inbreeding at the United States Department of Agriculture—A Progress Report

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Abstract
Inbreeding has progressed into the fourth generation of brother-sister mating in the Tamworth and Chester White breeds but only as far as the second generation in the Poland China breed. The results, as shown by weights, size of litter, mortality and sex ratio, are rather significant, except in the fourth generation, where the number of animals is too small to mean much. In breeding and Birth Weights The effect of inbreeding on birth weights is not consistent when considered in relation to the number of generations of inbreeding. The Poland China inbreds showed a decrease of nearly half a pound in mean birth weight from that shown by the non-inbred herd average. There was no difference between first and second generation inbred Polands. Among the Tamworths the first, second, third and fourth generation in-breds were either equal to or exceeded the non-inbreds in birth weight. The fourth generation pigs show a slight decrease. Among the Chester Whites the first generation pigs seem to be down in mean birth weight by about a half pound.

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