Rumination in sheep. II. The circadian pattern of rumination

Abstract

The rumination responses of caged sheep were measured under conditions of once daily, twice daily, and ad libitum feeding. The amount of rumination per day, in terms of the number of boli, the number of chews, and the number of chews per bolus, varied according to the level of intake and the physical and chemical composition of the food. Under once daily (at 0900 hours) feeding conditions the circadian (24-hr) pattern of rumination was characterized by a period of inactivity (lag period) after eating, followed by a period of increasing intensity of rumination leading up to a maximum intensity in the early hours of the morning, then a period of reduced activity up to the next feeding time. Where the detail of this curve varied it did so in accordance with consistent trends. For example, a high level of roughage feeding was associated with a shortened lag period and a less skewed distribution curve, while a low level of feeding resulted in a prolonged lag period and a highly skewed distribution. The pattern retained its general characteristics despite changes in the chemical and physical composition of the ration and despite variation in the method of administration of the ration. Circadian patterns resulting from twice daily (morning and afternoon) feeding varied according to the ingredients of the respective meals. Ad libitum feeding resulted in a loss of definition of the pattern; rumination tended to be distributed without apparent order over the whole day. It is suggested that the initiation of rumination after feeding, and subsequent rumination activity, is governed by some inhibiting factor(s).