Estimation of heterosis and heterosis retention in the development of a synthetic breed of goat

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references.Review of crossbreeding research indicates that the dominance model does not always adequately account for heterosis. With this in mind, genetic models were fit to goat crossbreeding data for type of birth, birth weight, and adjusted (for age) weights at two and four months of age. Data resulted from the development of a composite breed of goat in Kenya (KDPG) which is composed of 1/4 East African, 1/4 Gak 1/4 Toggenburg, and 1/4 Anglo-Nubian. Genetic models included a breed specific dominance model and epistasis models (also included breed specific dominance effects). The general epistasis models included direct and maternal effects for six two-locus configurations and direct and maternal linkage effects, but the majority of the maternal nonadditive effects were confounded and so this model was excluded from further analyses. Specific epistasis models excluded the linkage effects and made an assumption regarding the nature of epistasis (additive x additive, additive x dominance, or dominance x dominance). An additive effects model was also used as a basis for testing the significance of all the nonadditive genetic effects. All models included breed additive effects and fixed effects for type of birth (except for the analysis of type of birth), dam age, gender, birth year, and season of birth. Model comparisons were made to assess the importance of dominance and epistasis in explaining variation in performance. The specific epistasis models tended to be better than the dominance models. Model comparisons with the additive effects models also suggested that nonadditive effects were important. Performance of various crosses was also predicted from the model results and heterosis estimated. Heterosis estimates were generally negative possibly due to unaccounted for interactions among type of birth and the genetic effects and(or) due to inadequate estimation of the direct and maternal additive effects for the Nubian. Results suggest that use of Toggenburg, Nubian, and(or) KDPG bucks to be used to grade up the indigenous breeds would be advantageous