Abstract

Genetic diversity and flock clustering of a South African Dohne Merino flock selected for resistance to Haemonchus contortus Gastrointestinal parasitism is a major problem for livestock productivity worldwide and small ruminant production is affected the most. Resistance of gastrointestinal nematodes (GIN) to anthelmintics has become a widespread problem, with resistance of Haemonchus contortus in South Africa being one of the most severe. Farming with animals resistant to nematode infestation has been proposed as a sustainable alternative. The farm Wauldby in the Stutterheim district of South Africa has a well-documented history of heavy H. contortus challenge. In 2011, a project aimed at genetic selection for resistance to H. contortus was implemented at Wauldby. Annually, faecal egg counts (FEC), Famacha© score (FAM) and body condition score (BCS) were recorded on all lambs from weaning in January at 4 months of age, until the end of June when the H. contortus challenge decreased. Lambs were only drenched with an anthelmintic when they had a FAM of 2.5 or higher. Breeding values for FEC were estimated for Wauldby animals born from 2011 to 2014. In this study, genome-wide SNP data generated using the Illumina® Ovine SNP50 BeadChip was used to investigate flock clustering of the Wauldby Dohne Merino flock and its association with resistance to H. contortus. A total of 192 animals were selected for inclusion in the study. Within years, animals with the highest and lowest breeding values for FEC were selected among the animals that needed drenching (cases), and those that did not need any drenching (controls). Animals from the Grootfontein Dohne merino flock, which had not been subjected to any selection for resistance, were used as a reference population. The principal component analysis (PCA) plot was performed using SNP & Variation Suite (SVS) from Golden Helix to illustrate the population genetic structure of animals within the Wauldby Dohne Merino and GADI Dohne Merino sheep. Four distinct genetic clusters were observed, with the GADI Dohne Merino sheep population clustering separately. The Wauldby Dohne Merino population differentiated into 3 distinct clusters. Average FEC, LFEC (log-transformed FEC), BCS and FAM recorded over the study period were compared between the different clusters for the Wauldby animals. These results indicated that it should be possible to select for resistance to H. contortus on the basis of the phenotypic traits included in the study. Key words: body condition score, gastrointestinal nematodes, Famacha©, faecal egg count

Njabulo Mark Dlamini, Carina Visser, Pranisha Soma, Farai Catherine Muchadeyi, M.A Snyman

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Electronic Poster Session - Biology - Disease Resistance 2, , 230, 2018
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