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Abstract
AIMS: To document the Cu supplementation practices on dairy farms in the Waikato region, determine the Cu status of those herds, and compare the suitability of liver samples sourced from biopsies and cull cows for assessing Cu status.
METHODS: During spring 2008, concentrations of Cu, Mo and S were determined from pasture samples from 24 dairy farms. Feeding regimens, herd size, milksolids production, soil type, fertiliser policy and Cu supplementation practices were recorded for each property. Based on these data, 10 monitor farms were selected to represent a range of Cu intakes for herds, from 5 to 12 mg Cu/kg dry matter (DM). On each monitor farm 12 healthy lactating cows were selected for liver biopsy and collection of blood samples during the following autumn. Around the same time, livers were collected from 12 cull cows per farm when they were slaughtered, and samples of pasture were again collected from each farm. Concentrations of Cu were measured in all tissue samples.
RESULTS: Concentrations of Cu in pasture tended to be higher (mean 10.4 vs 8.2 mg/kg DM) in the autumn than spring, while concentrations of Mo were lower in the autumn (mean 0.35 vs 1.07 mg/kg DM). Most of the 24 farms used Cu supplementation in some form. Mean concentrations of Cu in liver for herds ranged from 640 (SD 544) to 2,560 (SD 474) µmol/kg fresh tissue in biopsies, and 520 (SD 235) to 2,610 (SD 945) µmol/kg in liver from cull cows. Mean concentrations of Cu in serum ranged from 7.9 to 13.4 µmol/L. The variability in concentrations of Cu for each farm was greater for liver (CV 50%) than serum (CV 21%). For individual cows, concentrations of Cu in liver, obtained by biopsy, and serum were not correlated.
CONCLUSIONS: The concentration of Cu in liver of dairy cows reflected widely differing dietary intakes of Cu between herds, although levels indicated an adequate Cu status on all farms in this study. Use of either biopsy samples or livers from cull cows were indicative of the Cu status of the herd. Wide variation in observed concentrations of Cu in liver indicated that at least 12 cows per herd should be sampled. On farms with intensive, long-term Cu supplementation programmes there is a risk of chronic Cu toxicity in some animals. Thus, the Cu status of dairy herds should be determined, and monitored, before making any recommendations regarding supplementation.
Acknowledgements
Our thanks to Matthew Brown of AgResearch for preparing the Waikato site map, to Fred Potter of AgResearch for statistical advice, to Joyce Voogt and Neil MacPherson for carrying out the liver biopsies, and to the following for providing facilities and cows for the study: John and Kathryn Blythe, Brian and Joanne Chick, Tony and Louise Collingwood, Robin and Pixie Moss, Barry McTamney and Nicola Marshall, Euan and Claire Reeves, Noldy and Bev Rust, Graham and Margret Shaw, Jim and Mary Grayling, and Shane and Sue Swinerd. This study was funded by AGMARDT, The Veterinary Centre in Te Awamutu, Bomac Laboratories Ltd, Merial Ancare NZ, and New Zealand Veterinary Pathology Ltd.