THE ROLE OF PH IN REGULATING RUMINAL METHANE AND AMMONIA PRODUCTION

When steers (n = 4) were fed increasing amounts of concentrate (0, 45, or 90% of DM) and decreasing amounts of forage, the VFA concentration increased (P < .001) and ruminal pH, acetate:propionate ratio, and di ssociated ammonia declined (P < .001). Acetate:propionate ratio and di ssociated ammonia were highly correlated (r(2) = .82 and .65, respecti vely) with ruminal pH. In vivo acetate:propionate ratio was highly cor related (r(2). = 78) with the capacity of the bacteria to produce meth ane from H-2 and CO2 in vitro, and in vivo pH dissociated ammonia was correlated (r(2) = .59) with the capacity of the bacteria to produce a mmonia from protein hydrolysate. The role of pH in regulating methane and ammonia production was supported by the effect of pH in vitro. Whe n bacteria from cattle fed concentrate or forage were incubated at pH values from 6.5 to 5.7, methane production decreased (P < .001) from 4 8 to 7 nmol mg protein-l min-l and from 14 to 2 nmol mg protein(-1) .m in(-1) respectively. The reduction in in vitro pH (6.5 to 5.7) also de creased (P < .001) the rates of ammonia production, but only if the ba cteria were obtained from cattle fed forage (28 to 15 nmol mg protein( -1). min(-1)). Bacteria from cattle fed 90% concentrate had similar (P > .05) rates of ammonia production at pH 6.5 to 5.7 (approximately 12 nmol.mg.protein.min(-1)). These results indicated that ruminal pH aff ected ruminal methane production, acetate:propionate ratio, deaminatio n, and ammonia concentration.