Studies of the food intake of sheep at a single meal.

I . Experiments are described in which the food intake and the water intake of sheep at a single meal were measured. The sheep were offered lucerne chaff ad lib. for z h only each day. 2. Following the peritoneal infusion of physiological saline the food intake increased, while the injection of a diuretic before feeding caused the food intake to be decreased. 3. In eight experiments the osmolality of the ruminal liquor was increased by the addition to the rumen of NaCl, KCl or the salts of volatile fatty acids in 250 ml water. The decrease in food intake was related to the osmolality, but not to the energy content, of the added electrolyte solution. In a further experiment, sheep receiving a highly digestible lucerne chaff, containing I yo (w/w) NaCl, increased their food intake when water was added to the rumen. Other workers have concluded that gastric osmolality is an important variable in the control of food intake in monogastric animals. The results of the eight experiments now described suggest that ruminal osmolality is of similar importance in ruminants. 4. It is suggested that all these observations are consistent with the theory, which has been proposed for non-ruminant animals, that the food intake at a single meal may be related to the degree of tissue hydration at the beginning of the meal.