Studies on the diet of the grazing animal. II. The effect of physiological status in ewes and pasture availability on herbage intake

Abstract

The digestible organic matter intake (DOMI) of ewes grazing Phalaris tuberosa–Trifolium subterraneum pastures was studied under controlled conditions. The variables studied were pasture conditions, breed, and physiological status of the ewe. The DOMI's of dry, pregnant, and lactating ewes were significantly related, in asymptotic form, to pasture conditions. About 40% of the variability in DOMI was accounted for by the total dry matter available per acre. Further variability was taken out by multiple regression in which diet digestibility, green pasture dry matter per acre, and leaf length were used. Regression models were similar for dry, pregnant, and lactating ewes. Dry and pregnant ewes within both breeds (2-year-old Border Leicester x Merino and 5-year-old Corriedale ewes) had similar DOMI's. The DOMI of lactating ewes was significantly higher than that of dry ewes within both breeds. The increase at the mean maximum intake was 50% for Border Leicester x Merino ewes and 25% for Corriedale ewes. The relative increase was greater at lower pasture yields and shorter leaf lengths. Intakes of Border Leicester x Merino ewes were substantially higher than those of Corriedale ewes although the ewes of both breeds were of similar weight. Reasons for this difference and the difference in lactation response on intake are discussed. Differences in grazing time and rate of eating were found between breeds and between ewes of different physiological status within breeds. The need for more detailed knowledge of grazing behaviour before these differences can be correctly interpreted is stressed.