Abstract:
Proc. Amt. Sot. Arlirn. Prod. I994 Vol. 20 THE EFFECT OF PHOSPHORUS DEFICIENCY UPON RUMINAL MICROBIAL ACTIVITY AND NITROGEN BALANCE IN LAMBS K.J. GUNN and J.H. TERNOUTH Dept of Agriculture. The University of Queensland, St Lucia, Brisbane, Qld. 4072 A depressive effect of phosphorus (P) depletion on microbial protein synthesis in goats has been observed but this effect was confounded by a depression in food intake (Petri et al. 1988). This experiment investigates the effects of P deficiency on ruminal microbial nitrogen (N) flow in lambs but taking the effect of P deficiency on food intake into consideration. The experiment consisted of 3 phases. In the first 4 week phase (Pl), 8 castrated Border Leicester crossbred lambs (27-32 kg) with ruminal and abomasal cannulas, were offered ad libitmz, a P supplemented diet. In the second IS week phase (PZ), these lambs were offered a P deficient diet. In the third 4 week phase (P3) the lambs were repleted with P but their food intakes were restricted to the lower food intake of PZ. The basal diet consisted of chaffed barley straw fed ad libitum, 90 g/day molasses, 10 o/day urea, 35 g/day gluten and 9 g/day vitamin-mineral mix. P was supplemented as monosodium a phosphate at 4 g/day. Digesta flow was measured using Yb and CrEDTA (Faichney 1980) and microbial 0 N flow using 35s (Mathers and Miller 1980; Elliott and Armstron, 1982). Flows and digestibilities were measured in the last 2 weeks of each phase. In contrast to the results of Petri et al. (19SS), the mean dry matter (DM) intake was not reduced in P2 although 4 lambs had intake reductions greater than 200 g in the final phase of P2, and all S lambs 0 had plasma inorganic P levels below 40 mg/L. Durin, P2, microbial N flow was reduced by 45%. The highest rate of microbial N flow was observed in P3. The flow of microbial N was not related to N balance. This experiment clearly shows that P deficiency causes a depression in ruminal microbial protein production regardless of the food intake of the lambs. Table 1. The effect of supplementation (Pl), depletion (P2) and repletion (P3) on the N and microbial kinetics (g/day) of lambs ELLIOTT, R. and ARMSTRONG, D.G. (1982). J. Agric. Sci., Camh. 99: 5 l-60. FAICHNEY, G.J. ( 1980). J. Agric. Sci., Camh. 94: 3 13 18. MATHERS, J.C. and MILLER, E.L. (1980). Bi-. J. Nuts. 43: 503- 14. PETRI, A., MUSCHEN H., BREVES G.. RICHTER 0. and PFEFFER, E. (1988). J. Agric. Sci., Camh. 111: 265-71. 445