A comparative study on the efficiency of water soluble phosphates and a dry phosphate lick for sheep fed on mature grass hay.

MYBURGH, S. J. & DU TOIT, J. DE V. A comparative study on the efficiency of water soluble phosphates and a dry phosphate lick for sheep fed on mature grass hay. Onderstepoort]. vet. R es. (1970), 37 (2), 127-136. In a study with adolescent Merino sheep on a diet of mature grass hay, the supplementation with phosphates alone, either in the drinking water or as a dry lick, did not prevent loss of condition. Furthermore, in metabolism studies the phosphorus and nitrogen balances under these conditons were negative. However, the daily inclusion of small allowances of lucerne hay and maize samp to the diet resulted in increased intakes of protein and carbohydrate and ensured positive metabolism balances for phosphorus and nitrogen. Under these improved feeding conditions body weights increased. The result of feeding this diet suggested that phosphate feeding at certain times may be unnecessary under practical conditions. INTRODUCTION Theiler (1920, 1931) first demonstrated that a phosphorus deficiency in the veld grass in some parts of South Africa during much of the year was responsible for stunted growth and characteristic bone lesions in cattle. These were, initially, incidental observations made after he had advocated the feeding to stock of sterilized bonemeal to prevent osteophagia, and thus lamsiekte, caused by the ingestion of carrion material containing the toxins of Clostridium botulinum. This feeding of bonemeal also corrected the phosphorus deficiency in the diet and prevented aphosphorosis. These findings stimulated investigations into various aspects of animal growth, blood composition and mineral content of the natural pasture, and on the efficiency of various phosphate supplements in the diet. The results of mineral metabolism studies led to the development of methods of administering inorganic phosphates to stock in their drinking water (Bekker, 1932; Reinach & Louw, 1952; Truter & Louw, 1952). Since certain water soluble phosphates were expensive at that time, a cheaper method was devised in 1952 by Reinach & Louw whereby defl.uorinated superphosphate could be safely used in the drinking water. The prescribed formula ensured an average daily intake of 5.7 g phosphorus by a bovine. Bisschop (1964) reported remarkably favourable results in an experiment in which the feeding of superphosphates in drinking water was compared with that of bonemeal. Deductions from farmers' reports on practical phosphate feeding, however, indicate that stock grazing natural veld do not always show such good results. It has also been demonstrated by Murray, Romyn, Haylett & Ericksen (1936) and Murray & Romyn (1937) that in the sandveld pastures of the Matopa area of Rhodesia, young growing stock and lactating cows did not benefit from the feeding of phosphates. Du Toit, Louw & Malan (1940) presented evidence that during the dry winter season of the summer rainfall area the extreme deficiency of protein in our pastures is possibly as important as the phosphorus deficiency. Furthermore, the digestibility of the desiccated vegetation determines the availability of the protein at various stages in the growth of the pasture (M yburgh, 1937; Louw, 1938; Louw, Bodenstein & Quin, 1948). The study presented here was initiated to confirm the theory that the ineffective results obtained in practical phosphate feeding were partly due to the low nutritive Received 13 March 1970.-Editor 127 state of the natural pasture. In similar studies on drought feeding of cattle, Morris (1958) reported that young heifers fed bush hay with mineral supplements, lost an average of 20 lb (9kg) body weight over a period of 26 weeks. In comparison, heifers fed additional daily supplements of 1.3lb (0.59 kg) and 3 lb (1.36 kg) of lucerne chaff per head over the same period gained an average of21lb (9.53 kg) and 28 lb (12.70 kg) respectively. In his experiment neither the body weight of the heifers nor their intake of hay was increased by providing a lick containing sterilized gelatinous bone flour. MATERIALS AND METHODS The project was divided into three separate experiments, in each of which the same animals were used. Sixteen adolescent Merino wethers, weighing between 34.6 and 36.8 kg, were divided into four groups, of which three received a different form of phosphate supplementation to their feed rations. The latter varied in each of the three experiments; in Experiment 1 it consisted of mature veld grass hay (i.e. the basal ration) ad lib.; in Experiment 2 the basal ration ad lib. plus 200 g lucerne hay a day per sheep, and in Experiment 3 the basal ration ad lib. plus a daily allowance per sheep of 200 g lucerne hay and 200 g maize samp (degerminated maize). The mature grass hay used throughout came from one large batch obtained from a single source. The phosphate supplements to the daily ration of the groups varied slightly in amount in the three experiments (see Table 1) and, apart from the control group which received no phosphate, were as follows :Group 1. Defl.uorinated superphosphate [prepared as described by Reinach & Louw (1952)] in the drinking water. Group 2. Monosodium phosphate in the drinking water. Group 3. Degelatinized bonemeal as a dry lick. TABLE 1 Daily intake of phosphorus (g) in respective rations Group Exp.1 Exp.2 Exp. 3 1. 1. 98 2.00 2 . 52 2. 1. 97 2.24 2. 57 3. 2.78 2.98 2 . 79 4. 0.45 0.69 0. 81 Before each experiment a period of adaptation to the feed and environmental conditions was allowed for at EFFICIENCY OF WATER SOLUBLE PHOSPHATES AND A DRY PHOSPHATE LICK FOR SHEEP TABLE 2 Chemical composition of the dry matter of rations (per cent) N Protein p Ca Ash Fibre (N X 6 . 25) Basal ration Exp. 1. Grass hay 0 .77 4.80 0 .075 0.35 2.25 36.3 2. " " 0. 76 4 . 80 0.07 0.32 2.20 36.0 3. " " 0.75 4.70 0.07 0.36 2.40 36.0 Feed Supplements : Exp. 2. Lucerne hay 2.56 16.20 0 . 17 1.12 8.9 28.4 3. " " 2.96 18.50 0 . 17 1.00 9 . 5 26.0 Exp. 3. Maize samp 1.26 7.90 0 . 05 0 .01 0.34 0.34 TABLE 3 Metabolism data. Retention of N, P and Ca