Ingestive behavior and short-term intake rate of cattle grazing on tall grasses

Tall grasses (>1 m tall) are an important forage resource for grazing ruminants. Understanding the ingestive behavior and short-term intake rate of cattle grazing on tall grasses will help facilitate grazing management of tall grass pastures. The aim of this study was to determine the allocation of jaw movements in grazing cattle in relation to tall grasses and to assess whether such allocations of jaw movements are effective for maintaining a short-term intake rate. Four plants were used as test plants: bahiagrass (Paspalum notatum Flügge; a short grass), Sudangrass (Sorghum×drummondii; a typical tall grass) and two growth forms of a dwarf bamboo (Sasa senanensis; a semi-woody form of tall grass): a naturally growing form (NGDB, approximately 2 m tall) and a form that is under grazing (DBUG,<0.8 m). Four Japanese Black cows were allowed to graze each plant in random order. The grazing jaw movements and intake rate were measured using an integrated method with a microsward technique and acoustic monitoring. The cows performed the highest number of total bites (simple bites+chew-bites) for bahiagrass, an intermediate number of total bites for Sudangrass and DBUG and the lowest number of total bites for NGDB (P<0.05). The total number of chews (simple chews+chew-bites) was similar among NGDB, DBUG, and Sudangrass, whereas the total number of chews for bahiagrass was less than that for dwarf bamboos. The number of observed chew-bites exhibited an order similar to that observed for the number of total bites. As a result of each jaw movement, cows ingesting the DBUG moved their jaws more frequently among the plants, and cows ingesting the bahiagrass performed the fewest grazing jaw movements. Bite mass was considerably greater in the cows ingesting NGDB than in the cows ingesting other plants. Conversely, the chew mass for bahiagrass was clearly greater than that for the two taller plants. Cows ingesting Sudangrass processed the least amount of forage with each chew (P<0.05). The intake rate did not significantly differ among the plants (P>0.05), except for Sudangrass. Cows ingested Sudangrass at a lower intake rate than observed for the other plants (P<0.05). The results suggest that cattle were able to control their ingestive jaw movements depending on plant characteristics such as height, the spatial arrangement of the leaves and leaf morphology. However, the lower short-term intake rate for tall grasses implies that there is a limit to the adaptability of grazing jaw movements.