THE DRY MATTER DIGESTION IN VITRO OF FORAGE CROPS

Abstract

An artificial rumen technique was evaluated as a method of determining the dry matter digestion of forages. The digestibility estimates obtained in the spring were significantly correlated (r = 0.77xx) with estimates obtained on these forages from a conventional digestion trial, whereas in the fall the coefficients were low and no longer significantly correlated (r = 0.49) with the conventional trial data.A medium maturing timothy polycross nursery was harvested at 10-day intervals throughout the first growth cycle. With the exception of the April 14th stage there were no significant differences in digestibility between the clones harvested in the early-leaf stage. Significant differences between selections were obtained in digestibility at later stages of maturity which may be a function of the leaf-stem ratio, the amount of leaf firing and thickness of the culms as well as changes in chemical composition. The per cent fructose content of this timothy herbage was significantly correlated (r = 0.78xx) with the dry matter digestibility only at the first stage of cutting.Changes in dry matter digestion using this artificial rumen technique were observed, with digestion estimates being higher during the spring and summer than during fall and winter.The method of drying herbage for these in vitro digestion experiments was studied with the conclusion that there was a significant difference in favour of freeze-drying. The dry matter digestion coefficients of the freeze-dried herbage were comparable to those expected for herbage of such quality digested in vivo.The use of an artificial rumen technique for estimating digestibility of clonal material shows promise for the plant breeder, providing certain precautions are taken. All lines to be screened should be included in a single trial to ensure maximum control of variables associated with technique. Samples should be uniformly processed, preferably freeze-dried, and digested with a single sample of rumen fluid.