highly significantp < 0.001
The risk associated with herd size was highly significant [p < 0.001] and very similar between the different genotype groups, generating odds ratios of 1.30, 95% CI [1.23, 1.37], 1.44, 95% CI [1.32, 1.58], 1.38, 95% CI [1.31, 1.45] and 1.37, 95% CI [1.32, 1.41] for genotypes 9:b, 10:a, 25:a and the combined genotypes, respectively.