Effects of ruminal fill on short-term herbage intake rate and grazing dynamics of beef heifers

Abstract

The impact of manipulating ruminal fill (RF) on intake rate of herbage and grazing dynamics was measured with three rumen-cannulated beef heifers grazing Bermudagrass pastures individually. The treatments compared were removal of proportions of rumen contents of 0 (treatment RF0), 0·33 (treatment RF33), 0·66 (treatment RF66) and 1·00 (treatment RF100). Treatments were randomly applied in a 3 × 4 Youden-square design. The rumens were emptied before and after planned grazing sessions (30 min) to set up the treatments, and to estimate intake rate and bite mass, respectively. Measurements were made of bite rate, bites per feeding station, feeding stations per minute, intake per feeding station, time per feeding station, eating and searching step rates and times. Apparent bite area and area grazed per feeding station were calculated. Ruminal fill affected short-term intake rate and changed grazing dynamics. As RF increased, step rates, searching times, bite mass, apparent bite area, bites per feeding station, area grazed per feeding station, time per feeding station and intake per feeding station decreased (P < 0·01) while step times, eating step rates and bite depth increased (P < 0·01). The results of the present study indicate that RF is an important factor governing the intake characteristics and behaviour of grazing beef heifers.