MECHANISMS OF HANDLING TIME AND INTAKE RATE OF A LARGE MAMMALIAN GRAZER

The effects of shard structure and bite weight (W) on bite rate in cat tle (Bos taurus) were examined to explain the behavioural components o f handling time. Three oesophageally fistulated steers grazed homogene ous, hand-constructed swards of Paspalum dilatatum Poir. or Medicago s ativa L., in a sward area of approximately 0.36 m2, for 60-212 s- Thre e types of jaw movements (JM) were distinguished: manipulative JM that gather herbage into the mouth, chewing JM, and compound JM that manip ulate fresh herbage and chew herbage already in the mouth within one c ycle 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 .0095W). Sward height and bulk density did not significantly affect I beyond the effects of W. Time per bite was 2.0 s when W almost-equal-t o 1.29 g, and increased linearly with when W > 1.29 g. Linear regressi on of time perbite on total number of JM explained 96% of the variance . A non-linear relation between total JM per bite and W comprised a li near relation between total chews per bite and W, and a constant numbe r 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 ov erlap of chewing and manipulation reached a maximum, so total JM incre ased with W. The importance of compound JM and the potential for overl ap between chewing and searching are discussed in the context of forag ing models.