Utilizing Genetics and Genomics to Improve Small Ruminant Production
Posbergh, Christian James
Sheep and goats are important livestock species producing meat, fiber, and milk. With the completion of these species’ reference genomes and decreasing cost of DNA sequencing, resources now exist to identify variation contributing to economically important traits. A hyperbilirubinemia and photosensitivity disease described in Southdown sheep in the 1940s was thought to be a model for Gilbert syndrome. Utilizing whole genome sequencing of a heterozygous individual we identified a single non-synonymous mutation in slco1b3 that causes the disease. This suggests that the disease appears to be an appropriate model for Rotor syndrome in humans, not Gilbert syndrome. U.S. lamb production is currently limited by the seasonal nature of sheep reproduction. It is difficult to reduce seasonality because it is only expressed in females, expressed later in life, and only observed in certain breeding systems. A high-density SNP chip was used to identify variation contributing to out of season lamb production through a genome-wide association study. This approach identified regions of the genome contributing to out of season lambing across multiple breeds and within the Dorset and Polypay breeds. Expected mature body size is a major driver of growth rate. However, selection for increased growth rate increases mature body size because the two traits are genetically correlated. Using twenty-eight body measurements on each of 616 mature ewes and a high-density SNP chip, several regions of the genome were associated with mature body size, including withers height, body length, and ear length. There is a wide variety of coat color variation within sheep. Utilizing community engagement and whole genome sequencing, DNA variation responsible for brown coat color and a dilution were identified in Jacob sheep. Work is ongoing to identify genotypic variants responsible for spotting, agouti alleles, and other patterns of sheep coat color. Application of genomics is a slow process. A large dairy goat herd introduced genomic selection rapidly due to the decreasing cost of sequencing. The data from the herd was used to show that genomics was more efficient than pedigree-based evaluation and that partial lactation yields were correlated with full lactation yields. This has allowed the herd to increase their rate of genetic progress.
aseasonality; coat color; genomic selection; GWAS; mature body size; whole genome sequencing
Clark, Andrew; Selvaraj, Vimal; Thonney, Michael; McEwan, John
Ph. D., Animal Science
Doctor of Philosophy
dissertation or thesis