A candidate gene approach to study nematode resistance traits in naturally infected sheep

Hazel Wilkie,Valentina Riggio,Oswald Matika,Louise Nicol,Kathryn A Watt,Rona Sinclair,Alexandra M Sparks,Daniel H Nussey,Josephine M Pemberton,Ross D Houston,John Hopkins

doi:10.1016/j.vetpar.2017.06.010

Hazel Wilkie, Valentina Riggio + Show 9 more

Open Access

https://doi.org/10.1016/j.vetpar.2017.06.010

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Abstract

Sheep naturally acquire a degree of resistant immunity to parasitic worm infection through repeated exposure. However, the immune response and clinical outcome vary greatly between animals. Genetic polymorphisms in genes integral to differential T helper cell polarization may contribute to variation in host response and disease outcome. A total of twelve single nucleotide polymorphisms (SNPs) were sequenced in IL23R, RORC2 and TBX21 from genomic DNA of Scottish Blackface lambs. Of the twelve SNPs, six were non-synonymous (missense), four were within the 3′ UTRs and two were intronic. The association between nine of these SNPs and the traits of body weight, faecal egg count (FEC) and relative T. circumcincta L3-specific IgA antibody levels was assessed in a population of domestic Scottish Blackface ewe lambs and a population of free-living Soay ewe lambs both naturally infected with a mixture of nematodes. There were no significant associations identified between any of the SNPs and phenotypes recorded in either of the populations after adjustment for multiple testing (Bonferroni corrected P value≤0.002). In the Blackface lambs, there was a nominally significant association (P=0.007) between IL23R p.V324M and weight at 20 weeks. This association may be worthy of further investigation in a larger sample of sheep.

Highlights

Young lambs are susceptible to parasitic nematode infection, which is a major economic and welfare burden to sheep production (Wright, 2013)
A total of twelve single nucleotide polymorphisms (SNPs) in IL23R, RORC2 and TBX21 were verified by sequencing genomic DNA in experimental Blackface lambs (Table 1)
This study identified SNPs within ovine TBX21, RORC2 and IL23R genes in an experimentally challenged Scottish Blackface population

Summary

Introduction

Young lambs are susceptible to parasitic nematode infection, which is a major economic and welfare burden to sheep production (Wright, 2013). Most lambs develop some level of protective immunity against the parasites (McRae et al, 2015). The use of genetic markers in selective breeding for resistant animals (currently selected based on lower faecal egg count (FEC), higher antibody (IgA) levels and higher weight compared to susceptible lambs; Beraldi et al, 2008) would allow for improved accuracy of selection and reduced need for routine phenotyping. An alternative is the candidate gene approach in which the effects of polymorphisms within genes of relevance to the trait of interest are investigated (Brown et al, 2013). In the case of nematode resistance, candidate genes include those that are involved in the immune response to nematode infection

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