Rates of change in liver copper concentration in cattle given a copper-deficient diet, with or without pre-treatment with tetrathiomolybdate, for evaluation of two parenteral copper supplements

Abstract

AIM: To minimise the impact of initial variation in liver copper (Cu) on assessments of Cu supplements for cattle in depletion/repletion experiments.

METHODS: Efficacy of two Cu injections was assessed with 18 calves, weighing 200–250 kg, given a Cu-deficient barley diet, containing 4.1 mg Cu/kg dry matter (DM) and added molybdenum (3 mg/kg) and sulphur (3 g/kg). Initial liver biopsy Cu ranged from 3.15–14.17 mmol/kg DM and nine calves with the highest values were given three subcutaneous injections of 235 mg tetrathiomolybdate (TTM) after 42–46 days depletion to lower liver Cu. Untreated (L) and TTM-treated (H) calves were ranked separately for liver Cu after 50 days depletion and allocated to one of three treatments: 100 mg Cu given subcutaneously as CuCaEDTA in either a paraffin (CuP) or aqueous base (CuA) after 56 days depletion (Day 0) or no injection (O). Thereafter, plasma and liver biopsy Cu were measured every 2–4 weeks for 16 weeks. Responses in liver Cu to Cu injections were compared with and without log_e transformation and by linear regression.

RESULTS: Prior to Cu injection, the fractional decline in liver Cu concentration (FDLCu) after 50 days depletion was 0.64 (SE 0.066) and 0.80 (SE 0.090) in H and L calves, respectively (p=0.09) and mean liver Cu did not differ on Day −6 (6.65 (SE 0.516) and 4.91 (SE 0.681) mmol/kg DM, respectively). Mean plasma Cu was higher in H than L calves on Day 0 (16.6 (SE 0.52) and 13.3 (SE 0.49) μmol/L, respectively (p<0.001)). Rates of decline in log_e liver Cu between Days 0–84 in treatments L and H were: 0.0138 and 0.0071 for Groups O; 0.0033 and 0.0016 for Groups CuP; 0.0073 and 0.0049 for Groups CuA (pooled SE 0.0014) mmol/kg DM/day, respectively. Between Days 84–114, FDLCu was uniformly high across experiments and groups (0.59 (SE 0.042)). Cu injections did not affect plasma Cu, which remained 3.1 (SE 0.41) umol/L higher in Experiment H than in L (p=0.017).

CONCLUSIONS: The use of rates of change in liver copper concentrations improved the assessment of efficacy for two parental copper supplements and that of pre-treatment with tetrathiomolybdate, which, contrary to expectation, slowed Cu turnover by mechanisms that remain unclear.

Keywords:

• Cattle
• copper-deficient
• copper supplement
• liver copper
• tetrathiomolybdate

Acknowledgements

I am indebted to Professor John Woolliams of Roslin Institute, Edinburgh, for statistical advice and Genstat analysis of liver Cu data; to the Clinical Department at Moredun Research Institute, particularly Jim Watt for his care of the stock and to Jim Williams for collecting liver biopsy and blood samples. I also thank John Small and Laura Burke of the former Biochemistry Department for all copper analyses. The experiment was conducted by Moredun Scientific Ltd. with funding by Glaxo Smith Kline Ltd. and the original experiment was funded by Pitman Moore. Neither party has contributed to this presentation and interpretation of results.

Notes

*Non-peer-reviewed