The effect of Christmas Island rock phosphate on grower pigs when fed as a calcium and phosphorus supplement

Abstract

Christmas Island Rock Phosphate (CIRP) is known to cause renal fibrosis and depressed growth performance when it is used as a source of calcium and phosphorus in grain based rations for grower pigs. As a result its full potential as an inexpensive mineral supplement has not been realised. This thesis presents a 4 part study of the toxic effects of CIRP and investigates the economic feasibility of including certain antagonists in rations containing CIRP. The data is discussed with special emphasis on aspects of economic importance for the pig industry. The results of the first experiment suggested that the initial renal lesion was focal interstitial fibrosis without obvious prior injury to glomeruli or tubular epithelium. Other evidence confirms the detrimental effect of CIRP on the growth rate of pigs. Evidence from the second experiment is presented to show that rations containing sodium fluoride produced similar kidney lesions to those induced by CIRP, and so support the hypothesis that the fluoride ion content of CIRP is responsible for the renal fibrosis. Additional evidence shows that the solubility of the source of fluoride is an important factor in the development of these lesions. In the third experiment, the absorption and storage of fluoride from 3 sources by young boars in metabolism cages was studied over a 20 week period. The results showed that absorption and storage of fluoride was greater when sodium fluoride was the source than when CIRP was the source. It was least when calcium fluoride was the There was source. no clinical evidence to suggest any of the 3 sources of fluoride had a detrimental effect on renal function. Results of the fourth experiment support the hypothesis that the addition of alumina and ground limestone in combination to rations containing fluoride is able to alleviate growth rate depression and prevent renal fibrosis. However they also show that the reduction in bone fluoride concentration which was achieved was insufficient to allow CIRP to be used at a 2% level in rations for other than pigs produced for market