Phosphorus supplementation at three sites along the digestive tract of sheep fed high and low calcium diets.

Abstract

Animal Production in Australia PHOSPHORUS SUPPLEMENTATION AT THREE SITES ALONG THE DIGESTIVE TRACT OF SHEEP FED HIGH AND LOW CALCIUM DIETS J.T.B. MILTON*, J.H. TERNOUTH*, E.A. WEIR* and B.J. MOON* SUMMARY Sheep were infused with supplementary phosphorus into the rumen, abomasum and caecum whilst fed a P deficient diet containing either high or low concentrations of Ca. When the P was infused into the rumen or abomasum, most of the additional P was absorbed, urinary excretion of Ca reduced and retention of Ca and P enhanced. Organic matter and water intakes were increased but organic matter and neutral detergent fibre digestibilities were not changed. One third of the infused P was absorbed by the caecum and colon. Relatively more P was absorbed, less lost in the urine and more Ca and P retained when the high Ca diet was fed. This indicates that it is desirable to feed supplementary Ca and P to ruminant animals consuming a low Ca-low P diet. INTRODUCTION Calcium (Ca) and phosphorus (P) are the two most plentiful minerals in the ruminant body and 99% and 78% are contained in the skeleton. The remaining P is present in the soft tissues, where it is involved in a range of metabolic activities (Fontenot and Church 1979; Ternouth 1980). Both Ca and P are absorbed mainly from the small intestine, the latter being absorbed in considerably larger amounts because of endogenous (mainly salivary) secretion. The regulation of the absorption mechanisms is not fully ,understood (De Luca 1979) but Cohen (1980) has suggested that the calcium status of the animal regulates the absorption of phosphorus. Field et cxl. (1%'5), Milt on and Ternouth (1979) and Sevilla and Ternouth (1980) have all observed that P deficiency but not Ca deficiency depresses food intake and digestibility in ruminant animals. However, recent evidence suggests that the effect of P deficiency upon food intake is independent of its effect on digestibility (Milton and Ternouth 1982). The stu,dy reported in this paper was designed to investigate the effects of supplementing phosphorus deficient diets by infusing additional phosphorus into the rumen, abomasum and caecum. The diets contained low and high levels of calcium. MATERIALS AND METHODS Six 2-year old Corriedale wethers (29-39 kg) were placed in metabolism crates in a continuously lit air-conditioned room for the experiment. Each sheep was fitted with vinyl catheters (1.5 ID, 2.5 mm OD, Dural) protruding 10 cm into the lumen of the rumen, abomasum and caecum and exteriosed through the para-lumbar fossae. To prevent leakage of digesta into the peritoneal cavity, the catheters were passed diagonally through the wall of the gastro-intestinal organs and sutured to the organ using lugs glued to the catheterThe experiment was designed as two 3 x 3 randomised blocks, in each of which three sheep were infused the supplementary P at the three sites. After a settlingin period of 21 days on the experimental diets, the sheep were infused with a saline solution at the selected site for a 10 d preliminary period, at a rate of 24.7 g NaCl in 0.87 L water (pH 7.1) during 6 equally spaced 2 hr infusion periods * Dept. of Animal Production, University of Queensland, St. Lucia 4067. 459 Animal Production in Australia each day. After the preliminary period the sheep were infused with the same volume of a solution containing 2.7 g P for 10 days at the same site. This solution contained 7.8 g NaH2P04.2H20, 7.2 g Na2HP04, 21.9 g NaCl and 1.2 g NaOH/L. The site of infusion was then changed and the second 10 d preliminary period begun immediately. Three of the sheep were fed a low Ca-low P (LCaLP) pelleted diet (15 mm diameter x 20-30 mm) composed of 60.8% barley straw chopped in a hammer-mill fitted with a 30 mm screen, 30.4% sugar, 6.5% gluten, 1.7% urea and 0.6% mineral vitamin mix to provide 10 MJ ME, 130g crude protein, 1.5 g Ca and 0.73 g P/kg DM. The high Ca-low P (HCaLP) pelleted diet fed to the other three sheep contained the same ingredien ts with an additional 3.3 g Ca/kg DM supplied as calcium carbonate. To ensure ad k%itwn consumption, the sheep were fed at a rate 20% above the intake of the previous day. Brisbane metropolitan water was available ad Zibitwn. During days 4-10 of the preliminary and experimental period the feed offered, refusals, faeces dried at 90�C and urine output were measured daily and sub-samples retained for analyses. Jugular blood (10 ml) was collected from each sheep prior to feeding on days 2, 4, 7 and 10 of each period and aliquots of plasm< taken for Ca and P determination. Ground (1 mm) sub-samples of feed offered, refusals and faeces dried at 90�C were analysed for dry matter and ash according to AOAC (1966) and neutral detergent fibre by the method of van Soest and Wine (1967). Feed, faeces and urine sub-samples were digested with a 4:l mixture of nitric and perchloric acids. The Ca content of digested samples and plasma was determined by atomic absorption spectrophotometry (Willis 1961). The method of Fiske and Subbarow (1925) was used to measure the P content of digested samples. Plasma inorganic P was determined on samples prepared according to Little et al. (1971). Because the LCaLP diet was fed before the HCaLP diet and 2 sheep on the HCaLP diet were replaced by LCaLP sheep, the results were statistically analysed using a non-orthogonal two-way classification. RESULTS The saline infusion had no effect upon food intake. During the final the settling-in and preliminary periods, the sheep consumed 1016 and 1019 g respectively. The site of the saline infusion had no effect upon food and intake, Ca and P absorption and retention or blood plasma levels. However, matter and neutral detergent fibre digestibility were significantly higher saline was infused at the rurnen than when infused at the other two sites. organic matter digestibility coefficients were 0.653, 0.610 and 0.607 (SE = respectively. 7 d of pellet: water organic when The 0.010) The five fold increase in the quantity of P available for absorption resultec in increased food and water intake, absorption and retention of P and plasma P concentrations when the P was infused into the rumen or abomasum (Table 1). Although Ca absorption and retention increased, this was largely associated with the increased food intake and reduced urinary losses rather than a change in the absorption coefficient. There was no effect of site of infusion upon organic matter or neutral detergent fibre digestibility. Calculating on the basis that there was no change in the apparent absorption of dietary P, the infused P was well absorbed when infused at the rumen and abomasum. The apparent absorption coefficient for the infused P was still 0.35 when infused into the caecum of sheep fed the P deficient diet. In the preliminary period, there were no differences between the LCaJ2 and 460 NS, Not significant; *, P < 0.05; **, P < 0.01; ***, P < 0.001 Animal Production in Australia HCaLP diets in any of the parameters measured except that for plasma inorganic P (3.72 vs. 2.22 mg%, SE = 0.18). When P was infused, the sheep fed the high Ca diet absorbed more Ca, lost less P in the urine and had a higher retention of both Ca and P than those fed the low Ca diet. The high dietary Ca resulted in an increased P absorption coefficient unassociated with any change in intake. DISCUSSION As the infusion of P into the caecum did not result in an increase in plasma P and the calculated P absorption was less than half that observed for the more cranial infusion sites, it can be concluded that when sheep are fed P deficient diets but the luminal concentrations of P are raised, most P is absorbed from the abomasum and small intestine, although the caecum and colon do have some capacity to absorb P. The forty percent increase in food intake observed when P was infused into the rumen and abomasum emphasises the importance of this mineral in limiting food intake but does not indicate whether the effect is due to the involvement of P in digestion or soft tissue metabolism. However, the digestibility of the organic matter and neutral detergent fibre were unchanged between infusion sites so it is unlikely that ruminal or caeco-colonic P levels were limiting microbial digestion. The absorption coefficient for P was enhanced, urinary losses suppressed and retention of Ca and P were higher when the sheep were fed the high Ca instead of the low Ca diet. These results suggest that mechanisms controlling P absorption are responding to the need for P for bone accretion independently of plasma Ca, probably by directly stimulating renal 1-a-25-dihydroxycholecalciferol production (De Luca 1979). In view of these results it is suggested that Ca and P supplements be given together to ruminant animals consuming low Ca-low P diets. ACKNOWLEDGEMENTS The authors wish to thank laboratory analyses. Thanks are of Tropical Crops and Pastures) The Australian CSIRO, Samford. support. Mrs. D.L. Burling for her help with some of the extended to Dr. L.J. Lambourne (CSIRO Division for organising the use of pelleting facilities at Wool Corporation is acknowledged for its financial REFERENCES A.O.A.C. (1966). 'Official Methods of Analysis.' Tenth edition (Association of Official Agricultural Chemists: Washington D-C.). COHEN, R.D.H. (1980 1. Livestock Prod. Sci. ,- 25. 7: DE LUCA, H.F. (1979). Nutr. Rev. 37: 161. FIELD, A.C., SUTTLE, N.F. and NISBG, D-1. (1975). J. Agric. Sci. 85: 435. E FISKE, C.H. and SUBBAROW, Y. (1925). J. Biol. Chem. 66: 375. FONTENOT, J.P. and CHURCH, D.C. (1979). In 'DigestivFPhysiology and Nutrition of Ruminants, Vol. 2 - Nutrition', p.56, editor D.C. Church-(0 Sr B Books: Oregon). LITTLE, D.A., ROBINSON, P.J., PLAYNE, M.J. and HAYDOCK, K.P. (1971). Aust. Vet. J. ,' 47: 153. MILTON, J.T.B. and TERNOUTH, J.H. (1979). Proc. Nutr. Soc. Aust. 4: 150. MILTON, J.T.B. and TERNOUTH, J.H. (1982). Proc. Aust. Soc. Anim. Trod. 14: 630. C SEVILLA, C.C. and TERNOUTH, J.H. (1980). Proc. Aust. Soc. Anim. Prod. 13: 449. 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