Influence of phosphorus content on feed intake and weight gain in sheep

Abstract

In two experiments penned sheep were fed the dry residues from subterranean clover based pastures. Phosphorus levels in the pelleted residues, produced by varying the rate of superphosphate application, ranged from 0.07 to 0.23 per cent. In addition, a high phosphorus ration was produced by the addition of inorganic phosphate salts. This supplement raised the phosphorus concentration from 0.07 to 0.30 per cent of dry matter. In both experiments, increasing the concentration of phosphorus in the dry feed by higher fertilizer rates resulted in: increased dry matter intake; increased percentage of dry matter digested (at least in one experiment) ; more phosphorus retained by the sheep (although on feed containing 0.1 1 per cent phosphorus or less, losses still exceeded gains) ; and increased body weight gains. Increasing the phosphorus content of the feed by use of an inorganic supplement gave: a smaller increase in dry matter intake; decreased digestibility; positive phosphorus balances; and an increase in body weight gain of about half that given by unsupplemented feed high in phosphorus. The results indicate that for maximum animal production, phosphorus concentrations needed in the dry feed are higher than those produced by fertilizing legume-based pastures at the lowest rate that gives maximum dry matter production. Near linear responses in body weight gains were obtained up to phosphate fertilizer rates of about three times those needed for maximum pasture yield.