Influence of increasing level of concentrate on the chewing time of the ration in dairy cow

Four different diets, made up of a grass silage and four concentrate supplies (0, 3, 6, 9 kg) were fed, in a latin square design, to eight dairy cows. Average dry matter (DM) intake of the animals was 14.5 kg for silage and 3.9 kg for concentrate. Animals had a live weight of 636 kg and their production was 15.8 kg fat-corrected milk. The total time of chewing was not significantly different between the treatments (average 940 min/day). After calculation, it possible to estimate the unitary chewing time of concentrate to 10 min/kg DM and that of forage to 62.5 min/kg DM; this last value is not influenced by the proportion of concentrate in the diet. This trial confirm that, for proportions of concentrate under 40%, the unitary chewing time of forage can be considered as constant.