Allometry of food intake and grazing behaviour with body size in cattle

SUMMARY In 2 years two groups of 32 grazing cattle were used to examine the effects of previous grazing treatment and of body size on grazing behaviour and herbage organic matter intake (HOMI). Compensatory intake resulted from differences in grazing time only in the first year. There were no sex differences in intake when account was taken of differences in mature size raised to the power 0·73. Bite weight was related to the degree of maturity by the allometric coefficient of 0·46, and HOMI was similarly related by the coefficient of 0·36. This accords with the predicted effects of restricted grazing conditions on animals of different weight, and with allometric changes with weight in incisor breadth. Decreases in intake under grazing were similar in animals differing in maturity and weight. It is suggested that under constant grazing conditions the change in grazed herbage intake as animals mature reflects the allometric change in bite weight and a corresponding decline in bite numbers, resulting in consumption of a constant proportion of ad libitum intake.