Phosphorus nutrition of beef cattle. 1. Effect of supplementation on liveweight of steers and digestibilty of diet.

The effect of phosphorus supplementation on liveweight and digestibility of dietary components was studied in two experiments with beef steers at Grafton, New South Wales. In one experiment, three groups of 15 steers grazed a pasture that was deficient in phosphorus and nitrogen throughout the year and received a supplement of 0, 35, or 70 g phosphorus each week for twelve months. The phosphorus supplements had no effect on liveweight. In a second experiment, five pairs of steers were individually fed a phosphorus deficient diet to which urea, molasses, and minerals were added. The steers received a daily supplement of either 0, 2, 4, G, or 8 g phosphorus. The supplements had no effect on liveweight or apparent digestibility of dry matter, energy, or nitrogen. The apparent digestibility of phosphorus increased with supplementation up to 4 g a day (P<0.001) but there was no further increase at the higher rates. The apparent retention of phosphorus increased with each increment of phosphorus (P<0.01). It is concluded that supplements of phosphorus will not improve liveweight performance when beef cattle graze natural pasture of such low quality as that frequently found in north-eastern New South Wales.