Abstract:
Proc. Amt. Sot. Anim. Prod. 1994 Vol. 20 EFFECT OF DIFFERENT DIETARY NITROGEN LEVELS ON MICROBIAL NITROGEN PRODUCTION AND EXCRETION OF PURINE DERIVATIVES IN CATTLE M.M. KOLADE, K.J. GUNN and J.H. TERNOUTH Dept of Agriculture, University of Queensland, Brisbane, Qld. 4072 Subject to the availability of sufficient energy, increasing the dietary ruminal degradable nitrogen intakes of cattle will increase microbial protein production. The microbial protein production may be monitored by the urinary excretion of purine derivatives (Chen 1989). Four young Friesian steers (170-185 kg liveweight) fitted with ruminal and duodenal cannulae were fed 4 isoenergetic diets which differed in dietary N (Table 1). The diets were based on oaten chaff, molasses and corn, in a latin square design. The cattle were supplemented with duodenally infused skim milk powder and whey to provide isonitrogenous total intakes (83-87 g/day). Digesta flow was measured using Yb and CrEDTA (Faichney 1975) microbial N using 355 (Walker and Nader 1975) and urinary allantoin as described by Borchers (1977) . Although the steers on all 4 treatments had similar organic matter (OM) intakes (4.2 kg/day), the quantity of OM digested in the rumen was lower for the lowest dietary N intake (Table 1). As the level of dietary N increased, there were increases in duodenal microbial N flow and, allantoin and uric acid in the urine. Allantoin was consistently about 88% of total excreted purine derivatives. There was a significant relationship between microbial N flow and the excretion of allantoin and total purine derivatives (Table 2). The results suggest the potential of this method to determine microbial flow in intact animals without the tedious procedures involved in the use of cannulated animals and markers. Table 1. Effect of diet on microbial N production, organic matter digestion and purine derivatives excreted (g/day). Standard error of means are in brackets. Table 2. Linear relationships (y = a + bx) between urinary excretion of purine derivatives (y; g/day) and microbial N flow (x; g/day: n = 16) BORCHERS, R. (1977). Anal. Bioch. 79: 612-7. CHEN, X.B. (1989). Ph.D. Thesis, University of Aberdeen. FAJCHNEY, G.J. (1975). In 'Digestion and Metabolism in the Ruminant', (Eds I.W. McDonald and A.C.J. Warner) pp. 277-91. (University of New England Publishing Unit: Armidale). WALKER, D-M. and NADER, C.J. (1975). Aust. J. Agric. Res. 26: 689-98. 387
