Genetics of flystrike, dagginess and associated traits in New Zealand dual-purpose sheep : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand

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Massey University
A literature review identified breech bareness, dagginess and fibre traits as potential indirect indicator traits for flystrike. Dagginess (faecal accumulation) had the greatest potential as an indirect indicator, and has been identified as an important trait itself. Therefore flystrike and dagginess were investigated for their associations with fibre and production traits. A genome-wide association study (GWAS) was performed to identify regions under selection and associated with these traits. Finally, a genomic selection (GS) analysis was performed for dagginess and dual-purpose production traits to estimate molecular breeding values (MBVs) and to determine their impact on the New Zealand dual-purpose selection index. Heritability, genetic and phenotypic parameter estimations were performed on a flystrike case-control dataset collected over 2 years. Flystrike had a heritability of 0.37, and high genetic and phenotypic correlations with dag score and a high genetic correlation with the coefficient of variation of fibre diameter. A similar analysis was performed on an existing New Zealand sheep industry dataset of about 2 million pedigree-recorded animals born between 1990 and 2008. The heritability for dag score at 3 and 8 months (DAG3, DAG8) was 0.34 and 0.31 respectively. There were low or nil genetic and phenotypic correlations of DAG3 and DAG8 with the other standard live weight, fleece weight, reproduction and faecal egg count production traits or breech bareness, fibre and wool traits. A GWAS performed on an industry dataset of 8,705 genotyped animals, using phenotype information on about 3 million pedigree-recorded animals, identified regions on chromosome 6 and 15 associated with DAG3 and DAG8. The lambs from the flystrike case-control dataset with SNPs imputed from 5K to 50K identified a number of immune, diarrhoea and wool/hair growth genes associated with flystrike, dag score and fibre traits in a GWAS. There were no similarities in the genes identified in the industry or case-control GWAS; however, the SNP on chromosome 15 was re-identified in the GS analysis for DAG8. The GS analysis showed that genomic predictions can be Genetics of flystrike and dagginess in New Zealand dual-purpose sheep performed for DAG3 and DAG8 and that using MBVs and modifying generation interval can increase the rate of the genetic gain of the dual-purpose index by 84% per year.
Flystrike, Myiasis, Sheep dags, Sheep breeding, Sheep genetics, Sheep disease prevention