Copper metabolism and requirement in mature ponies

The effects of copper intake on stable copper and 64Cu metabolism and on the excretory pathways of absorbed copper were examined in ponies. Bile and feces collected from two bile duct-cannulated ponies following an intravenous dose of 64Cu showed that bile was the main route of endogenous copper excretion. Stable copper and 64Cu metabolism were examined in three intact ponies fed dietary copper to provide 5.6, 16.6 and 25.7 mg Cu/100 kg body weight/day. The amount of copper excreted in urine was not influenced by dietary treatment. Stable copper absorption and 64Cu retention significantly increased when ponies were fed the low copper ration. A direct linear relationship was observed between 64Cu excretion in feces and copper intake. Isotope dilution methods and regression analyses of data from balance studies were used to estimate an obligatory copper loss in ponies of approximately 3.5 mg Cu/100 kg body weight per day. The estimated dietary copper requirement for maintenance of mature ponies was 3.5 ppm.