Seasonal and individual variation in hepatic copper concentrations in a flock of Norwegian Dala sheep

This study focused on a flock of Dala sheep with recurrent cases of chronic copper (Cu) poisoning. The seasonal variation in hepatic Cu concentration was followed in individual sheep with repeated liver biopsies, four times per year, in two consecutive years. Thirty-six ewes were included, yielding a total of 279 biopsies. Cu concentrations were measured by atomic absorption spectroscopy. Hepatic Cu concentrations remained almost stable from December to March, fell substantially from March to June, and rose sharply during the summer pasture period from June to October. There were large individual differences in hepatic Cu levels. These differences remained stable through the two years. Treatment with ammonium tetrathiomolybdate (3 × 3.4 mg per kg bodyweight (bw) s.c.) in June had only weak and inconsistent effect on hepatic Cu levels in October. The results may partly explain why chronic Cu poisoning in sheep in Norway predominantly occur in the autumn and winter months.