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Evaluation of Response to Selection of Sow Productivity and Construction of a Selection Index
Thesis Abstract:
The study attempted to examine the direct and correlated responses to selection and to construct a selection index for sow productivity traits. Data used were obtained from individual records of 1,468 pigs developed by a UPCA-NSDB special breeding project.
The method of fitting constants was used to determine the effect of known variation sources such as year, season, breeding group, sire and age of dam, on the traits under study. Since all these factors showed significant effects, data adjusted for age of dam were analyzed, using the statistical model containing all these sources.
A four-way nested classification was assumed and the variance-covariance components were computed from the model. Heritability estimates and environmental, phenotypic and genetic correlation values were obtained from the sire and within-sire components of variance and covariance.
Although found biased upward, heritability values for litter size and weight at birth and at weaning were within the range reported in the literature. However, large heritability values for birth and weaning weights were noted, owing to the nonvalidity of some of the assumptions and nature of the data used. Nevertheless, genetic and phenotypic relationships among the traits conformed with the findings of previous investigators.
On the basis of the evaluation and computation of the data on sow productivity traits, no selection index could be suggested on account of large sampling errors in the estimates of the genetic and phenotypic variance-covariance matrices.