Abstract

Resistance of Haemonchus contortus to anthelmintics in South Africa is a well-documented problem. In some areas, farming with animals resistant to nematode infestation seems to be the only solution in the long run. The farm Wauldby, in the Stutterheim district of South Africa, has a well-documented history of heavy Haemonchus contortus challenge and of Haemonchus resistance to all five major anthelmintic groups on the market prior to 2011. At the end of 2011, a project aimed at goal oriented selection for resistance to Haemonchus contortus was implemented in the Dohne Merino stud at Wauldby. Data on faecal egg counts (FEC), Famacha© score (FAM), body condition score (BCS) and log-transformed faecal egg counts (LFEC), recorded on the 2011- to the 2015-born lambs were analysed in this study. Between 10 and 12 two-weekly recordings of FAM, BCS and FEC were done each year. The number of individual data records available per year for these recorded resistance traits varied between 2365 and 3003 for a total of 13648 records. Various univariate, multivariate and repeatability animal models using the ASReml program were fitted to estimate genetic parameters for these resistance traits. The most suitable model of analyses for FAM, BCS, FEC and LFEC averaged over all recordings per year, included only direct additive genetic effects. Direct heritabilities of 0.20 ± 0.06, 0.32 ± 0.07, 0.15 ± 0.05 and 0.22 ± 0.06 were estimated for FAM, BCS, FEC and LFEC respectively. Direct heritability increased for all traits when data from all 12 available recordings were included. Various combinations of FEC taken at the different recordings were analysed in an effort to obtain the most suitable recordings for inclusion in a protocol for selection against resistance to Haemonchus. The combination of the 1st (January), 6th (March) and 9th (May) recordings yielded the most promising results. Genetic correlation among these three recordings for BCS (0.89 to 0.98), FEC (0.40 to 0.92) and LFEC (0.58 to 0.96) were high and positive. Univariate heritability estimates obtained for FEC and LFEC, averaged for the 1st, 6th and 9th recordings, compared well with those obtained under univariate analyses where all available data were averaged (0.16 vs. 0.15 for FEC and 0.20 vs. 0.22 for LFEC). However, it was much lower for FAM and BCS (0.02 vs. 0.20 for FAM and 0.23 vs. 0.32 for BCS). These results were used to develop protocols for selection for resistance / resilience to Haemonchus contortus in sheep under South African conditions. Keywords: faecal egg count, Famacha, body condition score, heritability

Magretha Anna Snyman, Willem Johannes Olivier, Allan Fisher

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Electronic Poster Session - Biology - Disease Resistance 2, , 288, 2018
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