Mechanisms of handling time and intake rate of a large mammalian grazer

Abstract

The effects of sward structure and bite weight ( W) on bite rate in cattle ( Bos taurus) were examined to explain the behavioural components of handling time. Three oesophageally fistulated steers grazed homogeneous, hand-constructed swards of Paspalum dilatatum Poir. or Medicago sativa L., in a sward area of approximately 0.36 m 2, for 60–212 s. Three types of jaw movements (JM) were distinguished: manipulative JM that gather herbage into the mouth, chewing JM, and compound JM that manipulate fresh herbage and chew herbage already in the mouth within one cycle of opening and closing of the jaws. Intake rate ( I, g min −1) was a discontinuous asymptotic function of W: I = W max(0.0337,0.0201 + 0.0095 ∗W) . Sward height and bulk density did not significantly affect I beyond the effects of W. Time per bite was 2.0 s when W ≈ 1.29 g, and increased linearly with W when W>1.29 g. Linear regression of time per bite on total number of JM explained 96% of the variance. A non-linear relation between total JM per bite and W comprised a linear relation between total chews per bite and W, and a constant number of total manipulative JM per bite. When W increased up to c. 1.5 g, chewing requirements were met by compound JM. Above W of 1.5 g, the overlap of chewing and manipulation reached a maximum, so total JM increased with W. The importance of compound JM and the potential for overlap between chewing and searching are discussed in the context of foraging models.