Copper concentrations in the liver and blood of sheep of different breeds in relation to swayback history

Abstract

The concentrations of copper in the blood and in the liver were determined for 68 female sheep of two age classes drawn from a genetically diversified grassland breeding flock. The flock comprised three breeds, Scottish Blackface, Cheviot and Welsh Mountain, and their crosses. Some sheep were inbred and some outhred, and they included a few which had produced swayback lambs two years previously. Constants were fitted for these various factors. They accounted for a significant proportion (31 per cent.) of the total variation in copper concentration in blood, but not in liver (17 per cent.). The copper concentrations ranked in the same order of magnitude for both blood and liver (Blackface < Cheviot < Welsh), but the crossbreds showed heterosis in blood copper concentration, but not in liver. The Blackface and its crosses had a significantly lower copper concentration in the liver than the three non-Blackface groups. Ewes which had formerly produced swayback lambs had a significantly lower blood copper level, but the level in the liver was average. There was a curvilinear relationship between blood and liver copper concentration. Expressed as the correlation between blood copper concentration and the reciprocal of the copper concentration in the liver, its coefficient was r = −0·6. The regressions of blood on liver values and vice versa were not significantly different for the various breeds except those for sheep involving the Blackface breed ( b blood. liver = 0·92 ± 0·20) and those excluding the Blackface ( b blood. liver = 0·17 ± 0·07). Copper concentrations in the liver was three times as variable, in terms of the coefficient of variation, as in the blood and this may contribute to the lesser significance of genetic variation in copper concentration in the liver than in the blood.