THE EFFECT OF PHYSIOLOGICAL STATUS ON DIET SELECTION BY GRAZING EWES

The effect of the physiological status of grazing ewes on diet selection was studied, using ewes with oesophageal fistulae. The diets of dry ewes grazing Phalaris annual grasses and subterranean clover pastures, over a range of availabilities, were compared with those of ewes in various stages of pregnancy and lactation. There were no significant differences at any stage of reproduction in the botanical composition of the diets. However, small differences in diet digestibility, soluble carbohydrate and nitrogen content were found during pregnancy and lactation. These occurred at all levels of availability of pasture. The differences did not appear to have nutritional significance in the particular pasture ecosystems studied because levels of N, soluble carbohydrates and digestibility of the diet were such that selection for survival was unlikely to be necessary. It is concluded that dry fistulated ewes can be used to obtain samples for assessing diet N and soluble carbohydrate contents for ewes in other physiological states. The use of in vitro digestibility tests of diets of dry ewes to assess diet digestibility for ewes in other physiological states may be subject to error.