In vitro studies on the effect of pH and of glucose on ammonia accumulation in the rumen of sheep

Abstract

The effect of pH and of glucose on ammonia accumulation in rumen liquor, obtained from sheep rumen contents, was studied during 4-hr in vitro incubations. Control of pH over the range 4.5-7.3 was effected with sodium phosphate-citric acid buffer. Casein hydrolysate was added as a substrate for ammonia production. There was an optimum pH for ammonia accumulation which varied between 6.0 and 6 . 7 on different diets, and which appeared to be correlated with the range of pH normally encountered in the rumen on each diet. Ammonia accumulation fell rapidly on the acid side of the optimum pH and usually less rapidly on the alkaline side. This effect of pH is most probably due to an effect on ammonia production, i.e. an effect on deamination of amino acids. Glucose reduced ammonia accumulation to an extent greater than could be accounted for by the fall in pH due to the fermentation of glucose; protein nitrogen levels in the reaction mixture were significantly increased. It was concluded that the effect of glucose was due largely to a stimulation of ammonia utilization for synthesis of microbial protein and not to an inhibition of ammonia production.