Recently, mixed inheritance model computer programs based on Markov Chain Monte Carlo methods have been developed with the ability to analyse extensive animal pedigrees. They partition the observed variation into variance due to: non genetic effects, polygenic effects, bi- allelic major locus effects and residual effects. They do not require genotype information. This technique was used to examine data from a randomly mated Coopworth sheep flock in New Zealand where faecal strongyle (FEC) and Nematodirus (NEM) nematode egg count information had been collected. All egg counts were initially transformed using the function logJx+50). The final model included the effect of sex/year contemporary group, birth day and polygenes in addition to a major, autosomal bi-allelic locus. Results from the analyses suggested a dominant autosomal gene for host susceptibility was affecting strongyle FEC values in the autumn period with estimates of 0.79 log eggs/g for the effect of a single allele, and a dominance effect of 0.96 log eggs/g. Host susceptibility for summer NEM was affected by a recessive gene with estimates of 0.64 and -0.68 respectively. The identification and characterisation of these QTL(s) may result in novel methods of internal parasite control

John C McEwan, R. J Kerr

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 27: Reproduction; fish breeding; genetics and the environment; genetics in agricultural systems; disease resistance; animal welf, , 335–338, 1998
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