Variation in the activities of glutathione peroxidase and superoxide dismutase and in the concentration of copper in the blood in various breed crosses of sheep.

Activities of the enzymes glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) were examined in the blood of 364 ewes of a lowland grazing flock comprising Scottish Blackface ewes and crosses of that breed with Border Leicester, Cambridge, East Friesland, Oldenburg and Texel rams. Half were bled at 16 months old and again two years later, and half at 28 months old. Variation attributable to breed of sire was not statistically significant (P less than 0.1) for GSH-Px, but was significant for whole blood copper concentration (P less than 0.01) and for SOD activity (P less than 0.05) although the latter was complicated by a large breed by age interaction involving two of the breeds. The correlation of SOD activity (per g haemoglobin) and whole blood copper concentration was 0.5, and the intraclass correlation between the estimates of SOD activities two years apart was 0.7.