SHORT-TERM THERMAL AND METABOLIC RESPONSES OF SHEEP TO RUMINAL COOLING: EFFECTS OF LEVEL OF COOLING AND PHYSIOLOGICAL STATE

Abstract

In a series of studies to simulate the ingestion of cold food, the rumen of adult sheep was cooled by 0–400 kJ over 1 h. Ruminal cooling reduced body heat content, increased rate of metabolic heat production and reduced apparent rate of heat loss to the environment. On average, each 100 kJ of cooling reduced heat content by 46 kJ, increased heat production by 20 kJ and reduced heat loss by 70 kJ. Precooling thermal status of the sheep affected the magnitude of the responses to cooling. A 0.1 °C higher precooling mean body temperature decreased the response in metabolic heat production by 6 kJ and increased the reduction in body heat content by 4.6 kJ. The heat production associated with eating reduced the heat loss response to ruminal cooling but did not affect the change in heat content. Well-insulated sheep were less affected by ruminal cooling. Key words: Sheep, rumen, cooling, heat production, temperature