Retention of copper in the liver of sheep genetically selected for high and low concentrations of copper in plasma

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Abstract
The extent to which genetic selection to change the concentration of copper (Cu) in plasma also affected the retention of Cu in the liver was assessed in three experiments. In each, the concentration of Cu was measured in samples of liver (taken by biopsy) and of plasma from female sheep of lines selected from a Scottish Blackface × Welsh Mountain population (which had previously been interbred for several generations) for high and low plasma Cu levels (high line and low line) and from purebred Scottish Blackface and Welsh Mountain females.The concentration of Cu in the liver and plasma was found to be consistently greater in high-line and Welsh Mountain than in low-line and Scottish Blackface females (P < 0·01) in the first experiment in which grazing animals were sampled at both 6 and 10 months of age and in the second, where sampling' was at 6 months only. Mean Cu concentrations in the liver ranged from 13 to 115 mg/kg dry matter (DM) and the correlations with those in plasma varied from 0·28 to 0·53 (all P < 0·05) and was highest when the concentration of Cu in the liver was lowest. The correlation between the concentrations of Cu in liver at different ages was 0·57 (P < 0·05).In the third experiment, 10-month-old high- and low-line females were given complete diets containing either 5, 10, 22 or 28 mg Cu per kg DM for 12 weeks. Liver samples were obtained at the beginning and end of this period and blood samples were taken every 3 weeks. The concentration of Cu in the liver was greater in high- than in low-line sheep on all diets and increased linearly with the Cu concentration of the diet but at a greater rate in the high line. At the end, the high line had significantly greater concentrations of Cu in plasma on the 5 and 10 mg Cu per kg DM diets.The experiments showed that high-line females retained more Cu in the liver than low-line females. It is most likely that this was caused by a positive genetic correlation between concentration of Cu in plasma and the efficiency of absorption of Cu.