An evaluation of the use of short‐term weight changes in grazing sheep for estimating herbage intake

Abstract A technique for estimating herbage intake by weighing sheep before and after grazing, with an allowance for insensible weight loss (IWL) was evaluated. Live weights were estimated by weighing each animal 200 times using an electronic balance and a microcomputer. This enabled each sheep to be weighed to ± 10 g and overcame the problem of fluctuation in weight due to movement. Mean rates of IWL in housed sheep were 2·3, 1·4, and 0·8 g min −1 for walking, standing eating or idling and when lying ruminating respectively. Intake rate (IR) estimated by weighing gave a small but significant bias of −0·8 g min −1 when compared with measurements of IR made using housed sheep. Estimates of IWL and IR were made with ewes grazing continuously stocked ryegrass swards maintained at surface heights of 3,6,9 and 12 cm. IWL was higher outdoors than indoors and tended to be higher on the longer swards. IR estimated by weighing gave similar results to those obtained using the chromic oxide technique. At a sward surface height of 3 cm, IR and total intake were lower than for taller swards and total time spent grazing decreased with increasing sward surface height.