Abstract:
Proc. Aust. Soc. Anim. Prod. (1974) 10; 111 DETRIMENTAL EFFECTS OF PHOSPHORIC ACID SUPPLEMENTATION OF BEEF COWS IN NORTHERN AUSTRALIA by M.J. PLAYNE* Phosphoric acid has been used widely as a source of supplemental phosphorus for cattle because it is convenient to add to liquid supplements or to supply through the drinking water (Mutch, 1970). In the study reported here, the effects of feeding 11 g P/day/cow as phosphoric acid through the drinking water on liveweight changes and pregnancy rates of grazing cows were examined. The design of the experiment has been described previously (Playne - al. 1973). et In 1970 and 1971, liveweight performance and pregnancy rates of cows receiving phosphoric acid did not differ from those of the control cows. In 1972 (severe dry season, no rain from mid March to mid January) 2.5 yearold cows of 436 kg mean liveweight and 3 to 4 months pregnant, were given supplements from 24th May. Their liveweight loss from then until the start of calving in November is shown in the table. Whereas During October, cows receiving Palone lost 53 kg/head. water intakes of groups I and III rose to 35 litres/day/head, those of both P groups dropped from normal winter intakes of 21 litres to 11 litres/day/ From 21 October'both P groups head between 21 October and 4 November. showed loss of appetite. Seventeen of the 19 group II cows were hand fed after 4 November but despite this four died. In contrast, the heavier cattle in group 4 were maintained on the experiment with no deaths although they lost weight rapidly during late October., The cause of the deaths is not known but may have been due'to the effects of low food intake and dehydration following reduced water intakes at a time when water requirements were increasing. The detrimental effects in 1972 could be associated with different concentrations of nutrients being available in the pasture in 1972. Most Stylosanthes humilis had been consumed by early October; thus a valuable source of calcium would have been depleted. L'Estrange and Murphy (1972) have shown that feeding mineral acids will cause negative calcium balance in Thus, one effect of phosphoric acid feeding may be to induce a calsheep. cium deficiency. Serum calcium was slightly depressed in the cows receiving phosphoric acid. REFERENCES L'ESTRANGE, J.L., and MURPHY, F. (1972). MUTCH, C.B. (1970). Qd agric. J. 96: 520. a Br. J. Nutr. 28: 1. PLAYNE, M.J., SIEBERT, B.D., and EDYE, L.A. (1973). Proc. III World Conf. on Anim. Prod., Melbourne (in press). * CSIRO Division of Tropical Agronomy, Pastoral Research Laboratory, Townsville, Queensland, 4810. 111
