The rate of dry matter disappearance from nylon bags of maize silage/grain diets as influenced by basal ration and processing of test samples

Abstract

Four maize silage/grain diets were incubated in nylon bags for up to 72 h in the rumen of non-lactating cows. The test samples were frozen and either finely ground or coarsely chopped. The cows were fed basal rations containing either 0 or 50% grain. Increasing grain content in the test samples was linearly associated with rate of dry matter disappearance ( k) and also with DM disappearance after 48 h in sacco. With k there was a significant interaction between processing of the test samples (grinding vs. chopping) and basal ration of the cows, but the ranking of the test samples was not influenced by either processing or basal ration. Rate of DM disappearance was also closely associated with DM digestibility measured in sheep ( r = 0.97; P < 0.01), but not with dietary metabolizable energy content as calculated from productivity data of lactating cows ( r = 0.75; P < 0.10). The possibility of interactions with other dietary nutrients would reduce the potential of nylon bag studies for assessing feeding value of mixed diets for milk production.