Graduate Thesis Or Dissertation
 

Association of genetically determined polymorphic blood components with prolificacies of purebred and crossbred pigs

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  • Crossmatings were accomplished among three semi-closed lines within a population of pigs, for the purpose of investigating effects of crossbreeding on reproductive traits. Two of the lines were purebred (Berkshire and Yorkshire); the third line ("Composite") consisted of descendants from inter se matings among offspring of crosses of the Berkshire and Yorkshire lines. Other crossbred categories consisted of offspring sired by members of the closed lines and farrowed by daughters which had been produced from Berkshire-Yorkshire crossmatings. Reproductive performance was expresses as number of fetuses (dead or alive) per litter. Demonstrations of genetic contrasts among the categories were accomplished by means of electrophoretic analyses of hemolysates and blood serum, and by serology of erythrocytes. Those methods were used to detect phenotypic variations in four serum proteins. two erythrocyte enzymes, and seven antigenic determinants located on the erythrocyte membrane. Among 275 pigs from which specimens were obtained for those analyses, there were dams which had produced a total of 480 litters. A sub-group among the subjects of those studies included 36 families consisting of a mated sow and boar, and one or more offspring of the mating. Inclusion of those families within the population of subjects provided opportunity for some verification of previously proposed modes of inheritance of the blood components. Certain alleles were found to be heterogeneously distributed among the Berkshire, Yorkshire, and Composite lines. Distribution of phenotypes among those categories was such that crossmatings could result in formation of heterozygous combinations of alleles which were found only in the homozygous state in the Berkshire and Composite lines. Distribution of alleles found at one locus was such that crosses of Yorkshires with either Berkshires or Composites could be expected to produce a phenotype which was not present in any of the Berkshire, Yorkshire, or Composite subjects. Those observations provided motivation for accomplishing blood component phenotyping on specimens from daughters produced from various types of crossmatings. Performance data on sows of separate breed categories (crossbred and purebred) were analyzed separately, as seven different subsets of the total performance data. Blood component phenotypes were shown to be associated with variance in reproductive performance, by the method of least squares analysis. Non-genetic variables also considered in these analyses were the age of dam at date of farrowing, and the semester during which conception occurred. Series of least squares analyses were accomplished with data from each of the seven different breed categories. Some evidence was found to suggest an overdominant mode of gene expression in certain breed categories. That mode of gene expression was correlated with the transferrin phenotypes in the Yorkshire and Composite lines, and with the amylose-modifier phenotypes in daughters of the Berkshire-Composite crossmatings. Somewhat less persuasive evidence also suggests an overdominant mode of gene expression correlated with the phosphohexose isomerase phenotypes in another crossbred category. The additive mode of gene expression was associated with transferrin and phosphohexose isomerase phenotypes in daughters from Berkshire-Composite crossmatings. Equally noteworthy results of the study were the consistencies in correlations of certain blood components with performance, without regard to whether gene expression appeared to be additive or non-additive. The evidence indicated high probabilities that transferrin phenotypes were real correlates of performance in three breed categories and that this was also true of amylose-modifier phenotypes in two of the breed categories. There was also fairly persuasive evidence that transferrin and amylose-modifier phenotypes were both real correlates of performance in two other breed categories as well.
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