Effects of buffer salts on feed intake, growth rate, rumen pH and acid based balance in calves.

Abstract

EFFECTS OF BUFFER SALTS ON FEED INTAKE, GROWTH RATE, RUMEN pH AND ACID-BASE BALANCE IN CALVES R.C. KELLAWAY*, T. GRANT+ and G.T. HARGREAVE* Inclusion of 2% NaHCO + 2% Na2HP0 or 4% NaHCO in calf diets increased feed intake and gr d wth rates. bh .en other soJr ces of Na were omitted, inclusion of 1% NaHCO + 1% Na2HP0 did not increase feed intake or growth rate. The median x-lid en pH was 5. Is and 5.8 on control and 4% NaHC03 diets respectively. Base excess in the blood was LO.12 and 9.45 mequiv./l on control and 4% NaHCO diets respectively; blood pH was maintained within the normal range o a the latter diet by a compensatory increase in pC02. I. INTRODUCTION Saliva production per unit food eaten is much lower in young ruminants (Wilson and Tribe 1961) than in adults (Balch 1958). NaHCO and Na. HP0 present in roughly equal amounts, are the major salts in saliva (Ka$ 19hi 6). Inclusion of NaHCO and Na2HP04 in concentrate pellets fed to young calves resulted in substa ;I tial increases in food intake and growth rate (Kellaway, Grant and Chudleigh 1973). This paper reports further on the effects of including buffer salts in concentrate pellets fed to calves. II. MATERIALS AND METHODS Friesian bull calves were used in all experiments. In Expt 1 calves were given milk replacer up to five weeks of age, as described previously (Kellaway, Grant and Chudleigh 1973). From one week of age, they were offered straw chaff and one of three types of concentrate pellets which were based on barley grain. The pellets offered were control (A), 4% mixed buffer salts (2% NaHCO + 2% Na2HP04) (B) and 4% NaHCO (C). Diets A and B were similar to thos 2 fed previously (Kellaway, Gran 2 and Chudleigh 1973) whereas diet C differed only in respect of the buffer salt; they contained 5.5, 17.4 and 16.4 g Na/kg dry matter respectively. Sixteen calves were allocated to each diet, and these were group-fed in pens, each of which contained eight calves. In Expt 2, calves were reared on one of two systems; weaning at 5 weeks of age and keeping on high protein pellets up to ten weeks of age (standard), or weaning at four weeks of age and transferring from high to low protein pellets between eight and ten weeks of age (early). The feeding regime up to four weeks of age was the same as in Expt 1 except that the pellets offered were control (A) and 2% mixed buffer salts (1% NaHCO, + $Na HP04) (D) which contained no NaCl and Na2S04. Both diets contaided abouz 6 g Na/kg dry matter. Sixteen calves were allocated to each of the four treatments and these were group-fed in pens each of which contain. ed eight calves. Individual live weights and feed intakes for each pen were recorded weekly. Analyses of variance were carried out only on liveweight data * Dairy Research Unit, Department of Animal Husbandry, University of A Sydney, Camden, N.S.W. 2570. Veanavite Pty. Ltd., Cowra, N.S.W. 2794. 273 for which individual animal observations were available. In Expt 3, diets A and C, together with straw chaff were each fed to four calves fitted with rumen cannulae. Jugular blood, collected weekly for five weeks after weaning at five weeks of age, was analysed for acidbase balance, using the procedures described by Billitzer and Jarrett Rumen pH was measured continuously for two 24 h periods, at six and eleven weeks of agerespectively. (1970) l - III. RESULTS AND DISCUSSION In Expt 1, the intake of pellets after weaning on diets A and B was 30% lower than that recorded with similar diets in a previous experiment (Kellaway, Grant and Chudleigh 1973). The pellets were of similar formulation and chemical composition, but may have differed in hardness. Despite this, intakes of diets containing buffer salts (B and C) were higher than that of the control diet (A), which resulted in higher growth rates, pre- and post-weaning, on diets B and C than on diet A (Table 1). It appears that NaHCO alone was as effective in increasing intake as the mixture of Na2HP04 an a NaHC03. NaHC03 is considerably cheaper than Na2HP04. TABLE1 177 and 156 kg on the standard and early weaning systems respectively. The growth rate up to ten weeks of .age was significantly lower on the early weaning system (Table 2). The main effect of Expt 2 was that the total intake of pellets was Two per cent mixed buffer salts were included in diet D because we found previously that 2 and 4% levels of inclusion were equally effective in increasing feed intake and growth rate (Kellaway, Grant and Chudleigh NaCl and Na SO4 were omitted in order to reduce the sodium concentration because z he currently recommended level is 1 g Na/kg dry matter (National Research Council 1971). There was no difference in feed intake between the control diet (A) and the diet containing buffer salts (D) and growth rates were similar on the two diets. This suggests that the responses obtained in our earlier work (Kellaway, Grant and Chudleigh 1973) and Expt 1 were attributable to Na rather than the buffer anions. Saville - al. (1973) found that at 6-7 g Na/kg dry matter, NaCl and et buffer salts were equally effective in increasing the intake of wheat alone, which contained 0.02 g Na/kg dry matter. High levels of Na in the diet either as NaCl (Hemsley, Hogan and Weston 1975) or mixed buffer salts *. 274 1973) l (Harrison - al. 1975) increased rumen dilution rate and reduced the proet portion of organic matter digested in the rumen. An increased flow rate of digesta through the rurnen could minimise physical limitations to intake. Although the intake of concentrate diets in adult cattle is limited by chemical rather than physical factors (Baumgardt 1970) the small size of the rumen in calves normally may impose physical limitations to the intake of concentrate diets. The acid-base measurements in Expt 3 (table 3) indicate that with 4% NaHCO in the diet there was a large base excess, which was attributable to th$ bicarbonate. Although this caused an elevation in blood pH, there was a compensatory increase in pC02 which resulted in blood pH remaining within the normal range for calves (Donawick and Baue 1968). Rumen pH in these calves (table 4) was markedly affected by diet. The median pH values were 5.3 and 5.8 on the Control diet and the diet containing 4% NaHCO respectively. These pH values were similar to those reported by Kay, sell and Boyne (1969) for steers fed barley and barley plus 7.5% NaHC03 respectively. They found extensive pathological changes in the rumen wall of steers on the barley diet which were absent from steers given the NaHCO supplement. It seems likely that the higher intake which we observed a n diet (C) was at least partly mediated by the higher rumen pH 275 TABLE 4 on this diet which would have provided more favourable conditions for ruminal microbiota, as well as reducing the possible incidence of pathological lesions in the rumen wall. Current collaborative studies aim to define the intake response curves with different levels of NaCl and NaHCO in the diet, and also 3 to elucidate the response mechanisms. IV. ACKNOWLEDGMENTS We would like to thank Mr. Phillip Grant for care and management of the calves and Miss S. 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