Studies of the toxicity of copper to pigs

Abstract

1. Six groups of three (Expt 1) or four (Expt 2) female litter-mate Large White pigs were allocated after weaning to three or four treatments in a randomized block design. 2. In Expt 1, 600ppm copper were added to diets based on maize meal and containing either soya-bean meal, dried skim milk or white-fish meal to provide 16% total crude protein. Severity of Cu toxicosis was assessed by estimating aspartate transaminase (AST) activity in serum, Cu levels in serum and liver, haemoglobin concentration and the incidence of jaundice. 3. Toxicosis was severe only in pigs receiving white-fish meal, but liver Cu and haemoglobin levels were similar in all groups. 4. In Expt 2, 0, 250 or 425 ppm Cu or 425 ppm Cu+150 ppm zinc+150 ppm iron were added to the maize-white-fish meal diet from which the normal Zn and Fe supplements were omitted, creating optimal conditions for development of Cu toxicosis. 5. In the absence of Zn and Fe supplements, 425 ppm Cu caused the development of a severe toxicosis. Simultaneous addition of Zn and Fe supplements eliminated all signs of toxicosis. 6. Under the same conditions 250 ppm Cu caused a mild toxicosis and also exaggerated the slight signs of parakeratosis or Zn deficiency noted in control animals. 7. High calcium levels of 1.7% in a basal diet containing 30 ppm Zn probably induced a marginal Zn deficiency which favoured the development of Cu toxicosis. Differences in calcium level were probably responsible for the apparent effects of the different protein supplements in Expt 1. 8. Occasional occurrences of toxicity in pigs given 250 ppm Cu as a growth stimulant may be partly due to the use of diets low in Zn and Fe and high in calcium. Correcting these factors would extend the safety of Cu supplementation of the commercial diets.