Short-term ingestive behaviour of cattle grazing tropical stoloniferous grasses with contrasting growth forms

Abstract

SUMMARYRelationships between sward height and short-term ingestive behaviour of cattle were examined for two tropical stoloniferous grasses with contrasting growth forms: centipede grass (Eremochloa ophiuroides(Munro) Hack.; (CG); strongly prostrate) and bahia grass (Paspalum notatumFlügge; (BG); more erect). Turves (500×500 mm) were extracted from field monoculture swards of each grass after the varying duration of re-growth, and presented to animals for a short period (10 bites) to measure bite dimensions (area, depth and volume), bite mass, time per bite and intake rate. In the same re-growth period, CG was always shorter and denser than BG. Bite dimensions, the bite mass and the intake rate of animals increased at a declining rate as the sward height increased for both grasses, showing a tendency for a steeper initial increase, an earlier plateau and a lower maximum in CG than in BG. Due to the difference in the shape of the intake rate response, animals on BG were estimated to require a longer grazing time than those on CG to attain the same daily herbage intake, when the sward is shorter than about 200 mm. The sward height below which the daily intake of animals may be restricted was lower for CG (61–70 mm) than for BG (71–92 mm). The results indicate an advantage of strongly prostrated, highly dense grasses (e.g. CG) over more erect, less dense grasses (e.g. BG) when grazed at a relatively low height (<200 mm). In relation to increasing bite mass, the time per bite pooled over CG and BG was constant until the bite mass reached a critical value (0·55 g dry matter (DM)) and thereafter increased linearly with the bite mass, confirming that cattle are able to perform compound jaw movements that gather herbage into the mouth (manipulative jaw movement) and chew herbage already in the mouth (chewing jaw movement) within one cycle of opening and closing of the jaws.