Herbage intake parameters of sheep and cattle compared with simulated grazing by animal jaws : a dissertation submitted in partial fulfilment of the requirement for the degree of Bachelor of Agricultural Science (Honours) in the University of Canterbury [Lincoln College]

Abstract

Indoor grazing of three hoggets and three heifers, average liveweight of 40 and 152 kg respectively, took place on intact perennial ryegrass (Lolium perenne) / white clover (Trifolium repens) swards that had been removed from the ground. The intake parameters intake per bite (IB) and rate of biting (RB) were measured. Simulation of grazing with sheep and cattle jaws then took place on similar swards to allow comparison with the live animals. The effect of sward structure appeared to have little effect on the intake parameters of the live animals, although the technique of placing a grid in the sward to determine the horizon grazed caused considerable variation in results. The average herbage height appeared to have a larger effect on cattle compared with sheep, the cattle IB being 17 and 5 mg DM bite ⁻¹ (W ⁰·⁷⁵) ⁻¹ at herbage heights of 15 and 7 cm respectively, whereas the IB of sheep remained at approximately 8 mg DM bite ⁻¹ (W ⁰·⁷⁵) ⁻¹ regardless of herbage height. This compares with other authors of an IB of sheep at a herbage height of 15 cm. The reason why the IB of sheep did not fall was not accurately determined, although a hypothesis was made. RB was observed to decrease as the herbage height decreased contrary to the findings of other authors. This was explained by the animals sending a greater time perceiving the sward. IB of the jaws was not significantly different (P>0,05) at the different pasture horizons (151 (+64) and 40 (+15) mg DM bite ⁻¹ for cattle and sheep respectively). The distance the jaws were opened (% open - the percentage of the maximum) had differing effects for sheep and cattle jaws. Increasing % open of sheep jaws from 25 to 100% increased IB from approximately 25 to 50 mg bite ⁻¹ regardless of horizon grazed. With cattle however, increasing % open implied a greater IB only if grazing the top (>9 cm) horizon. Some of the variation between species was explained by a model. When IB was corrected for the width of jaw (across incisors), the ratio of IB for jaw live animal was approximately 1: 2.6 for both sheep and cattle. The ratio of IB for sheep : cattle was 1.4 : 1 for both the live animal and jaws, suggesting that cattle have a physical advantage in intake compared with sheep. Hypotheses on why this occurs were presented.