Antioxidants in blood from sheep lines divergently selected for facial eczema resistance

Abstract Romney sheep have been evaluated for resistance to facial eczema (FE) using a process which involves challenge with the FE toxin, sporidesmin, and they have been bred in selection lines for increased resistance (R) or susceptibility (S) to FE. There is evidence that sporidesmin exerts its toxic effects by generating reactive oxygen species, and protection can be afforded by a number of antioxidants and antioxidant enzymes. Our objective was to summarise three separate experiments to determine whether the R and S lines differed in antioxidant mechanisms, in search of a non‐invasive genetic marker. Lines were compared for the activities of four enzymes in blood in Experiment 1, superoxide dismutase (SOD), catalase (CAT), glu‐tathione peroxidase (GPX), and glutathione reduct‐ase (GR), and for the concentration of the tri‐peptide thiol, glutathione (GSH). SOD, CAT, and GSH were also recorded in Experiment 2, and GPX alone in Experiment 3. Heritabilities were estimated for SOD, CAT, and GSH. SOD activity was lower and CAT activity was higher in the R than in the S line (P < 0.01 for both enzymes). GPX activity was higher in the R than in the S line in Experiment 1 (P = 0.002) and Experiment 3 (P = 0.06), whilst neither GR activity nor GSH concentration differed significantly between lines. Heritability estimates for SOD, CAT, and GSH were 0.19 ± 0.11, 0.63 ± 0.14, and 0.34 ± 0.14, respectively. It is concluded that selection for divergence in sensitivity to sporidesmin in sheep may have been successful partly because of correlated responses in activities of three antioxidant enzymes (SOD, CAT, and GPX), capable of scavenging reactive oxygen species. However, the divergence between resistant and susceptible sheep in blood antioxidant activity was not large enough to be a reliable indicator of individual FE resistance.