Magnesium phosphates as dietary supplements for growing sheep

SUMMARY Growing wether sheep in metabolism cages were fed a low phosphorus diet (0·75g P/day) supplemented with 1·75 g P/day as either a magnesium phosphate (20·0% Mg, 18·5% P) or a calcium magnesium phosphate (16·1% Ca, 6·0% Mg, 18·5% P). In addition, the magnesium phosphate provided 1·87 g Mg/day and the calcium magnesium phosphate 0·57 g Mg/day. In each case comparisons were made with equivalent amounts of phosphorus and magnesium supplied as dicalcium phosphate (26·5% Ca, 16·0% P) and magnesium oxide (60·0% Mg). All the supplements resulted in similar positive phosphorus retentions of between 0·77and 0·92 g P/day compared with a daily loss of 0·17 g P/day for the low phosphorus diet. Calcium retentions were higher (1·40 and 1·70 g Ca/day) whendicalcium phosphate rather than the magnesium phosphates (1·16 g Ca/day) were given. Magnesium retentions were increased from 0·1 g Mg/day (unsupplemented) to 0·3–0·4 gMg/day and were similar for both magnesium oxide and the magnesium phosphates. Blood phosphorus and magnesium concentrations were increased to a similar degree by all forms of supplementation.