Abstract

Differences in the Cu status of two flocks of Romney lambs were observed which suggest that lines of sheep having distinct Cu metabolism have been identified. As part of a larger study relating Cu intake to Cu status of grazing lambs, changes in concentrations of Cu in liver, plasma and other tissues, and in erythrocyte Cu/Zn superoxide dismutase (SOD) were monitored for 176 days in two flocks of 50 sheep. The animals grazed on ten experimental paddocks treated with 0, 0.4 or 4 kg Cu/ha which resulted in mean pasture herbage Cu concentrations of 8 (Control), 13 (Low), and 41 (High) mg Cu/kg DM. At the start of the experiment these lambs, sourced from two Wairoa farms, had markedly different liver Cu reserves (1270 v 190 mmol Cu/kg FW, flocks H and L respectively) which could not be attributed to Cu supplementation. This difference between flocks was maintained throughout the 176 day study for sheep grazed on control pastures, through day 99 for sheep on the low pastures, and for 51 days in sheep on the high paddocks. High copper intakes increased liver Cu concentrations to as much as 4800 mmol (300 mg) Cu/kg liver FW after 99 days, with no signs of chronic Cu toxicity. Initial flock differences in liver Mo concentration (14.7 v 20.6 mmol Mo/kg FW, n=10, P<0.05) disappeared by day 51. The first measured SOD activity (day 51) in flock H was 17% greater than that of flock L (1600 v 1370 U/g Hb, n=21, P<0.01) and this flock difference was maintained through day 142 and day 99 for sheep grazing control and low pastures, respectively. SOD activity was found to be a reasonable predictor of liver Cu stores only in sheep having low to moderate Cu intake. Had the differences in initial liver Cu concentration and in blood Cu/Zn SOD activity of the two flocks been merely a reflection of the Cu and Mo status of their respective Wairoa farms, the disparity would have been expected to diminish much more quickly than was observed in this study. Factors controlling Cu metabolism are heritable. Trials selecting for differences between flocks in liver Cu concentration are needed to establish whether these flocks are genetically distinct in the way they metabolise Cu.

SO, Knowles, JR Rounce, ND Grace, and J Lee

Proceedings of the New Zealand Society of Animal Production, Volume 58, , 195-198, 1998