Abstract
The purpose of this paper is to describe development of an in vitro procedure for estimating ruminal protein degradation of pasture herbage. The procedure involves the use of freeze-dried grass as an incubating material and short-term (2hr) incubation of rumen fluid without artificial saliva in a modified syringe. When grass samples which were prepared by three kinds of drying treatment such as freeze-drying (f.d.), oven-drying (o.d.) and sun-curing (s.c.) were incubated with rumen fluid, ammonia release from f.d. sample was largest. In the case of f.d. sample, it was calculated that ammonia is derived from not only the non-protein nitrogen components of grass but also from the true protein fraction. Thus the degradation of herbage protein was demonstrated. However, in the case of o.d. or s.c. sample, the evidence of protein degradation was still obscure in such a short-term incubation. It was concluded that f.d., in preparing grass sample for in vitro rumen fermentation, is reasonable by means of providing the nearest one to fresh grass. The in vitro incubation was also done with six f.d. samples in which crude protein (CP) and total non-structural carbohydrate (TNC) contents ranged from 14.4 to 24.4% and from 9.5 to 19.6%, respectively. There was found a positive correlation between the CP content of grass sample and the ammonia release. Since the chemical analysis of grass samples revealed a negative correlation between their CP and TNC contents, it is pointed out that CP/TNC ratio of grass is important because it influences the extent of ammonia release. The ammonia release derived from the degradation of herbage protein was discussed from the point of easy metabolizability of both CP and TNC. On the validity of the in vitro procedure, the paper was also discussed firstly the short-term incubation, connecting with the rapid fermentation of herbage CP and TNC, and secondly needlessness of artificial saliva on the basis of the short-term incubation.
