Abstract:
Proc. Aust. Soc. Anim. Prod. I996 Vol. 21 EFFECT OF DIETARY PROTEIN LEVELS ON MICROBIAL NITROGEN FLOW FROM THE RUMEN M.M. KOLADE and J.H. TERNOUTH Dept of Agriculture, The University of Queensland, St Lucia, Qld 4072 A major goal of feeding regimens is to maximise microbial protein flow to the small intestine (Clark et al. 1992). This experiment investigated the effect of dietary protein concentration on microbial protein flow from the rumen of cattle fed high energy diets. Six Braford steers (210 + 5.5 kg liveweight) were randomly assigned to six diets in a 2 x 3 factorial experiment (2 grains and 3 levels of protein) based on l/3 chopped pangola hay and 2/3 wheat or sorghum meal mixed with soybean meal to provide 100, 120 and 140 g crude protein/kg DM in the final diets. The cattle were housed in metabolism crates. After 8 weeks of transition and adjustment to the grain-based diets, they were offered their respective diets ad libitum for a period of 2 weeks with total urine collection on the last 5 days. In a second and third period the steers were fed the same grain but a different protein level allowing a further 9 days between changing diets and sampling (Smith and McAllan 1970; Spicer et al. 1986). The urine was analysed for allantoin (Birchers 1977) to estimate microbial nitrogen flow (Kolade et aZ. 1994). As there was no interaction between grain type and protein level the mean result for the grains is presented. Table 1. Intake of organic matter (OM) and nitrogen (N) by steers, rumen ammonia-N concentration , daily excretion of allantoin and the estimated microbial nitrogen (MN) flow from the rumen. . There were no significant difference in the organic matter intakes of the cattle, but the rumen ammonia, allantoin and, by calculation, microbial nitrogen flow from the abomasum increased as protein concentration increased (Table 1). The allantoin excretions indicate that microbial protein flow increased by 40% when dietary protein was increased from 100 to 140 g/kg DM, and that feeding these higher levels of dietary protein in grain-based diets increased microbial protein flow. BIRCHERS, R. (1977). Anal. Bioch. 79: 6 12-7. CLARK, J.H., KLUSMEYER, T.H. and CAMERON, M.R. (1992). J. Dairy Sci. 75: 2304-23. KOLADE, M.M., GUNN, K.J. and TERNOUTH, J.H. (1994). Proc. Amt. Sot. Anim. Prod. 20: 387. SMITH, R.H. and McALLAN, A.B. (1970). Br. J. Nutr. 24: 545-56. SPICER, L.A., THEURER, B.C, SOWE, J. and NOON, T.H. (1986). J. Anim. Sci. 62: 521-30. 448