EFFECT OF COPPER SUPPLEMENTATION ON THE COPPER STATUS OF PASTURE-FED YOUNG THOROUGHBREDS

The effect of copper supplementation of pasture fed mares and feats on the copper status of the foals, in terms of plasma, soft tissue and b one copper concentrations and caeruloplasmin activity, was investigate d. Twenty-one Thoroughbred foals from either control mares (n = 9), or copper-supplemented mares (n = 12) were divided randomly into control (pasture only, n = 10) or supplemented (pasture and oral copper sulph ate, n = 11) groups. The pasture diet was grazed by all animals, and c ontained 4.4-8.6 mg Cu/kg dry matter (DM). The copper supplement for t he mares contained copper sulphate equivalent to 0.5 mg Cu/kg liveweig ht (LW)/day. This daily dose was converted to allow administration as a thrice weekly dose (i.e. multiplied by 7/3) which was given for 13-2 5 weeks prior to foaling. The supplemented foals, also dosed 3 times a week, received 0.2 mg Cu/kg LW/day at age 21 days, which was increase d to 0.5 mg Cu/kg LW/day at 49 days and was continued at this level un til euthanasia at 150 days. Foal plasma copper concentration and caeru loplasmin activity increased from birth to 21 days post partum and the n plateaued at a concentration similar to the mare, but the rise in th ese indices was not affected by copper supplementation of the mare or foal. Copper supplementation of the foal increased fod liver copper co ncentration at 150 days (P<0.03), Copper intake of diets containing ap proximately 8-28 mg Cu/kg DM is web reflected by liver copper concentr ation, but is poorly reflected by bone, other soft tissue copper conce ntrations and circulating copper status indices.