Genetic and environmental influences upon litter size and variation of birth weights in Berkshire swine Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dj52w810p

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  • Litter site and birth weight data compiled from the farrowing records of 275 litters out of 109 purebred Berkshire sows of the Oregon State University swine herd during the years 1953 to 1960 inclusive were used in this study. Genetic and environmental factors influencing four components of reproductive performance, namely, within litter variance of birth weights, litter size, number born dead and mean birth weight of pigs within a litter were evaluated by the method of stepwise multiple regression analysis. The estimate of within litter variance of birth weight was greater for larger litters but was decreased as the inbreeding coefficient of the litter increased. Litter size was depressed as inbreeding of dam increased; however, due to the structure of the herd there was an unusual positive relationship between inbreeding of litter and litter size. The latter observation leads to the conclusion that litter size is more strongly influenced by the genotype of the sow than by the genotype of the offspring. The number born dead in a litter increased as litters became larger. A disproportionate number of highly productive sows kept in the herd to advanced ages brought about an unusual ace-of-dam effect; there was, however, no basis for establishing that a greater number of dead pigs occurred in litters out of sows of different ages. The average birth weights of pigs within litters was smaller in larger litters. Average, birth weight was also decreased as the inbreeding of dam increased. Age-of-dam effects were not found to be important for any of the components of reproductive performance studied nor were consistent environmental effects found. An analysis of variance of sib groups was used to derive estimates of repeatability and heritability for within litter Variance of birth weights, litter size and litter weight. Data for these analyses were taken from the farrowing records of 44 scars which had farrowed two or more litters. The estimates of repeatability of within litter variance of birth weights was 0.02. This indicates that there was no tendency for sows to exhibit permanent differences for this character. The repeatability estimates of litter size and litter weight were 0.208 and 0.135 respectively. The heritability estimates of litter size as derived from the dam and sire component of the covariance of half sibs were 0.198 and 0.237. The estimate of heritability of litter weight at birth was 0.199. From these estimates it appears that progress from selection for improvement in all of the components of reproductive performance would be slow. An increased rate of progress will require a more accurate identification of superior genotypes Which can be accomplished, in part, by stabilizing temporary environmental factors.
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