Butting by calves, Bos taurus, and rate of milk flow

During nursing, the young of many ungulates butt at their dams' udder, which has been hypothesized to reflect difficulty obtaining milk. We investigated the effect of manipulating milk flow rate on the butting behaviour of domestic calves sucking milk from an artificial teat. The lowest rate of butting during nutritive sucking occurred with the fastest flow rate, and the highest rate of butting occurred with the slowest flow rate. When milk flow rate was changed during a meal, calves butted more following a decrease in flow rate than following an increase in flow rate. Butting rates were consistent and relatively low with a constant flow of milk. Regardless of flow rate, calves butted more at the beginning of their meal compared with the middle and end. Overall, the highest butting rate occurred when milk flow stopped, either at the end of the meal or when milk flow during the meal was stopped repeatedly for 30-s periods. We conclude that calves are sensitive to variations in milk flow rate and that butting rate changes accordingly. The occurrence of butting by young ungulates during nursing thus may indicate either a stoppage of milk flow or a decrease in milk flow rate, and thus may help identify periods of nonnutritive sucking during nursing. (c) 1998 The Association for the Study of Animal Behaviour.