Epsilon Archive for Student Projects

Abstract

Recent developments in the field of genetics have enabled the easy identification of individuals carrying known genetic defects, even in the absence of phenotypic expression. One such defect, known as gonadal hypoplasia, has affected the Swedish Mountain Cattle since the start of the 20th century. Gonadal hypoplasia is a defect characterized by small, underdeveloped gonads, often resulting in impaired reproductive function and fertility. The defect has been associated with homozygosity of a ~500 kb region on bovine chromosome 29. This region, known as the Cs29 allele, has also been linked to the colour-sided phenotype which is characteristic of the breed. This correlation together with earlier decisions to favour the colour-sided animals likely explains both the initial increase in gonadal hypoplasia and its continued presence within the breed today.

The aim of this study was thus to evaluate potential breeding strategies against hereditary gonadal hypoplasia to ascertain how the frequency of the disease-associated allele, and the number of hypoplastic animals can be decreased while maintaining genetic diversity of this vulnerable local breed. To achieve this, the project focused on three objectives. 1) Develop a simulation of a deleterious genetic variant under balancing selection, resembling the Cs29 allele in Swedish Mountain Cattle. 2) Simulate and evaluate alternative breeding strategies against gonadal hypoplasia, using phenotypic and genetic testing. 3) Evaluate the impact of the various breeding strategies on the effective population size (Ne) in the simulations.

The results show that, compared to the current policy of phenotypic selection, strategies utilising genetic information to facilitate selection against the defect appear better suited to reduce both the frequency of the deleterious allele and the frequency of affected animals. However, the results also highlight clear trade-offs between reducing the prevalence of gonadal hypoplasia and two other critical aspects: namely preserving the breed’s genetic diversity and limiting the amount of genetic testing required to achieve the reduction.