Molecular genetics of flystrike susceptibility in New Zealand sheep

Abstract

Flystrike is a problem for most sheep industries worldwide as it affects animal welfare and production. The cost of flystrike is multifactorial, and includes production losses resulting from reductions in wool and body growth, morbidity, and treatment and control costs. Flystrike incidence is environmentally dependent and its prevalence is variable. However, several factors predispose individual sheep to flystrike, such as variation in the fleece and skin of the sheep, and variation in their immune response. Identifying genes that are involved with these factors and the predisposition to parasitic disease, will potentially allow for flocks to be genetically improved for flystrike resilience, thus reducing its impact in the NZ sheep industry. This study aimed to identify variation in five candidate genes associated with phenotypic factors that do, or may, predispose sheep to flystrike, and determine whether the genetic variation (if any) was associated with susceptibility to disease. The genes chosen had either previously been implicated in resistance to fleecerot (FBLN1 and FABP4), or potentially affected the wax content of the fleece (ABCC11), or were involved in immune response (TLR4 and RASGRP1). In the sheep studied, variation in ovine FABP4, FBLN1 and RASGRP1 was associated with susceptibility to flystrike. Sheep with the A1 variant of FABP4 were found to be less likely (P = 0.014, with an odds ratio of 0.689) to have flystrike than those without A1. The likelihood of flystrike occurrence continued to decrease as copy number of A1 increased from one copy to two (P= 0.002, with an odds ratio of 0.674). The FBLN1 B1 variant was found to be associated with reduced flystrike occurrence (P = 0.029, odds ratio = 0.286), while the FBLN1 C1 variant was associated with increased occurrence (P = 0.002, odds ratio = 1.687). The RASGRP1 A (P = 0.015, odds ratio = 1.557) and C (P = 0.047, odds ratio = 0.733) variants had a significant association with flystrike occurrence. This study showed identified FABP4, FBLN1 and RASGRP1 as good candidate’s genes for flystrike resilience in sheep. Further research is required to verify these genes as markers for flystrike resilience.