BITE DIMENSIONS AND HERBAGE INTAKE BY CATTLE GRAZING SHORT HAND-CONSTRUCTED SWARDS

The objectives of this study were to contribute to the understanding and quantification of the effect of sward structure on the ingestive behavior and intake of livestock. Hand-constructed swards of approximately 0.43 m2 were used to determine the bite dimensions, bite weight, and short-term intake rate of steers (Bos taurus L.) grazing short swards. Swards were constructed of leaf blades of Paspalum dilatatum Poir. at homogeneous heights of 0.04, 0.06, 0.08, and 0.10 m and heterogeneous heights with means of 0.06 and 0.10 m at two leaf densities. Treatments were replicated using three 4-yr-old steers. Bite depth (B) was defined as the initial sward height (H) minus the mean residual height of grazed leaves. Bite area (A) was defined as the surface area represented by the mean number of leaves grazed per bite. Leaf density had no effect on bite dimensions. Linear regression of B on H and linear regression of A on H explained 99% and 89% of the variance, respectively. Mean bite weight ranged from 0.053 to 0.807 g. Correlation of measured bite weight with the product of the measured B, A, and bulk density yielded a coefficient of determination of 0.97. Mean intake rate ranged from 131 to 1473 g h-1. Bite weight accounted for 93% of the variance of intake rate. Bite dimensions on heterogeneous swards were similar to those on homogeneous swards, though by different mechanisms. The importance of biting overlap, leaf insertion in the mouth, and tongue sweeping are discussed in relation to mean bite dimensions and weight.