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The effects of cadmium in feed, and its amelioration with zinc, on element balances in sheep¹

C. J. C. Phillips^*,,2, P. C. Chiy^*, and H. M. Omed

^* Department of Clinical Veterinary Medicine, University of Cambridge, Cambridge CB3 0ES, U.K. and and Department of Agricultural and Forest Sciences, University of Wales, Bangor, Gwynedd LL57 2UW, U.K.

² Correspondence: School of Vet. Sci., Univ. of Queensland, Gatton 4343, Australia (phone: 617 33469179; fax: 617 33651255; e-mail: c.phillips{at}uq.edu.au).

The effects of feeding Cd to sheep at a level that is typical of polluted regions were investigated, as well as possible amelioration by adding Zn to the diet. Welsh Mountain ewes (n = 24) were fed herbage and concentrate in metabolism crates, with four supplement treatments in a two-factor factorial design: no supplement, Cd supplement only, Zn supplement only, and a combination of both the Cd and Zn supplement. Cadmium (286 µg/kg of feed DMI) and Zn (8.6 mg/kg feed DMI) were added as sulfates. Food and water intakes and element balances were recorded over 20 d after 7 d dietary adaptation, and element concentrations were determined in wool samples. Neither metal affected DMI or digestibility (P > 0.15), but water intake (P = 0.001) and urine output (P = 0.03) were decreased when only the Zn supplement was added. Water retention was increased by the Cd supplement (P = 0.04). In wool, the Cd supplement greatly increased the K concentration if no Zn supplement was fed (P = 0.02), and the Zn supplement decreased Mn concentration (P = 0.02). Cadmium in feed increased the Cd balance and produced several mineral disturbances, in particular a decrease in Na balance that is typical of renal tubular disorders. Adding Zn as well as Cd to feed returned the Cd balance to a level similar to that of sheep receiving neither Cd nor Zn, which suggests that Zn status is critical in determining whether Cd in feed increases the Cd balance in sheep. Feeding Cd also increased urinary K, Fe, Mo, Cr, B, and Ca concentrations, even when supplementary Zn was fed. It is concluded that low levels of Cd in sheep feed can increase the Cd balance if adequate Zn is not provided, which can lead to subclinical mineral disturbances and changes in the mineral concentrations in wool.

Key Words: Absorption • Cadmium • Sheep • Toxicity • Wool • Zinc

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