965 1 We are grateful to the staff of Theix experimental farm for taking care of the animals, and to B. Mallet and G. Toporenko for excellent technical assistance. We also thank P. D’hour, I. J. Gordon, and M. Picard for their comments on the manuscript. 2 To whom correspondence should be addressed. Received July 21, 1997. Accepted December 14, 1997. How Readily Will Sheep Walk for a Preferred Forage? 1 B. Dumont 2 , A. Dutronc, and M. Petit INRA, Lab. Adaptation des Herbivores aux Milieux, Centre de Clermont-Fd/Theix, 63122 St-Gene `s-Champanelle, France ABSTRACT: 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. Key Words: Food Preferences, Walking, Learning, Sheep 1998 American Society of Animal Science. All rights reserved. J. Anim. Sci. 1998. 76:965–971 Introduction As pasture quality decreases, sheep continue to choose high- rather than poor-quality forages as long as possible (Grant and Hodgson, 1986; L’Huillier et al., 1986; Dumont et al., 1995). We used an indoor method (Dumont and Petit, 1995) to study how ewes chose between a good-quality hay, the accessibility of which we varied, and a poor-quality hay freely available. We offered the good hay in limited quanti- ties every time a ewe walked across the test area. We varied its accessibility (ratio of reward to distance) by changing 1 ) the quantity that rewarded the walk and 2 ) the distance to be walked for the reward. Some- times, good hay accessibility was the same, with different distances to be walked to reach it. We could thus assess how walking was affected by forage reward, distance to walk, and ratio of reward to distance. The aim was to gain understanding of the movements of an animal grazing a two patch-type mosaic, in which preferred patches varied in biomass and spacing. We tested whether an energy gain maximization hypothesis (Pyke, 1984) would account for the diet the ewes selected. Materials and Methods The experiment was conducted from November 1995 to April 1996. We conducted training sessions in November and December to select 10 ewes from an initial group of 17, which we then tested for choice from January to April 1996. Animals and Forages. We used Limousin ewes born in March and April 1995; they weighed on average 39.3 (SD 4.6) kg during testing. They were fed a natural mountain pasture hay harvested at mid-ear emergence (8.6% CP [Kjeldahl N × 6.25], 31.5% crude fiber [CF; AOAC, 1990], and .56 OM digestibility [pepsin-cellulase method; Aufre `re and Michalet- Doreau, 1983]) and a concentrate that supplied 25% of their energy needs. We weighed the ewes every 3 wk and adjusted feed quantities to requirements (INRA, 1989); ADG was 72 g/d. The ewes were tested for their choice between a poor-quality and a good-quality hay, both from mountain pastures. The poor-quality hay (8.6% CP, 37.3% CF, and .51 OMD) had been harvested in good weather conditions at the flowering stage and was chopped to 5 cm to limit selective feeding. The good-quality hay (13.5% CP, 31.6% CF,