How readily will sheep walk for a preferred forage?

We studied how ewes chose between a poor-quality hay freely available and a good-quality one offered in limited quantities when they walked across an indoor test area. To determine what dictates a ewe's behavior, we varied the accessibility of the good hay by changing the quantity that rewarded the walk (2, 4, 8, 16, or 32 g) and the distance walked (23 or 46 m). Ewes were more reluctant to walk for the good hay as reward level decreased. For a given reward, average preference for good hay (P(GH)) also fell when ewes had to walk 46 m to be rewarded. In each comparison, for the same reward to distance (Rew/Dist) ratio, average P(GH) did not differ. We determined the correlation between P(GH) and Rew/Dist using data from three experiments with ewes offered a similar choice. The best model accounted for 85% of the corrected total sum of squares. Good hay procurement cost thus dictated a ewe's behavior. Choice was suboptimal only, either due to the test conditions, discrimination errors, or an animal's will to select a mixed diet. Our results suggest that, within its perceptive field, a ewe will equally walk to resources that have the same edible biomass relative to the distance to the patch.