Preliminary association of microsatellite heterozygosity with footrot in domestic sheep

Genetic heterozygosity in wild, unmanaged animal populations is often associated with protection against infectious disease. However, little is known about the relationship between heterozygosity and disease susceptibility in domesticated livestock, where disease resistance has the potential to improve animal welfare and productivity. We have investigated whether susceptibility to footrot, an important cause of poor welfare and reduced productivity in sheep, is associated with heterozygosity at 14 candidate microsatellite loci. Heterozygosity at locus BMC5221 was associated with resistance to footrot (P = 0.0034). This locus was selected based on a gene ontology classification of ‘response to Gram-negative bacteria’. Sheep homozygous at BMC5221 were at increased risk of virulent footrot (OR = 4.8, 95% CI = 1.5–15.3), with a dose response relationship between homozygosity and disease severity. A highly significant homozygote deficit was observed in sheep without virulent footrot (observed = 4, expected = 21, χ2 = 13.76, P = 0.0002) but not in sheep that had clinical disease, suggesting homozygotes were disproportionately likely to contract virulent footrot. Our results indicate that genetic heterozygosity might be important for healthy immune function in domesticated livestock. The use of gene ontology codes might prove a useful