The Effects of Selective Breeding for High or Low Clean Fleece

Blood was sampled from sheep of 3 flocks, selectively bred for either high (Fl+) or low (Fl-) clean fleece weight or randomly bred (R). Under maintenance (M) and, subsequently, sub-maintenance (0.8xM) or supra-maintenance (1.6xM) feeding regimes, Fl+ sheep had significantly lower concentrations of cystine in plasma than R sheep, which in turn had significantly lower concentrations of cystine than Flsheep, indicating a probable negative genetic relationship between clean wool production and plasma cystine concentration. The average concentration of glutathione in the red blood cells of GSHH sheep (i.e. sheep with higher concentrations of reduced GSH in their red blood cells, due to the action of a single dominant gene) was significantly greater in Flsheep than in Fl+ sheep, with R sheep having the lowest concentration. Within flocks, there was no significant correlation between cystine in plasma and glutathione in the erythrocytes. The concentrations of both metabolites were greater in blood sampled from the sheep on 1.6xM than in those on 0.8xM (P < O.Ol), but there was an interaction (P < 0.05) between flock and ration for GSH.