No evidence for a universal association between variation in faecal egg count for a mixed field-challenge of gastrointestinal parasites and the presence of the Ovar-DQA1 null haplotype in sheep

We tested the association of the Ovar-DQA1 null haplotype with faecal egg count (FEC) in 4676 male lambs sourced from 185 different sire-lines and four breeds. For each lamb a faecal sample was collected at weaning (approx. 4 months of age) and mid-autumn (approx. 9 months of age) and each was typed for the presence of Ovar-DQA1 null. General Linear Mixed Models (GLMMs) were used to analyse the relationship between FEC and Ovar-DQA1 null, both across and within breeds. Two models were used, the first testing the effect of the presence/absence of Ovar-DQA1 null and the second testing the effect of the number of copies of Ovar-DQA1 null present in an animalʹs genotype (i.e. dominant/recessive or additive effects). Across the breeds, no significant effect of the presence of Ovar-DQA1 null on FEC for Nematodirus sp., Strongyle genera, or total FEC was detected at either 4 or 9 months of age using either of the models. Within breeds, significant associations were detected at 4 months in South African Meat Merinos, with the presence of Ovar-DQA1 null in an animalʹs genotype being associated with a lower strongyle (absent: n = 23, geometric mean = 135 epg; present: n = 10, geometric mean = 67 epg; P = 0.025) and total FEC (absent: n = 23, geometric mean = 220 epg; present: n = 10, geometric mean = 121 epg; P = 0.017). These associations were not detected at 9 months of age.