The effects of intra-ruminal loading with cold water on thermoregulatory behaviour in sheep.

1. Shorn sheep exposed to ambient termperatures of 5 degrees C soon learned to turn on infra-red heaters by placing their muzzles through a photoelectric beam, although before shearing they did not operate the heaters. 2. The duration of infra-red heating obtained decreased at higher ambient temperatures and at 25 degrees C very little heat was obtained. 3. When infra-red heaters totalling 900 or 1800 W were suspended above the sheep they turned on the 900 W heaters for almost exactly twice as long as they did the 1800 W heaters when exposed to 10 degrees C for 24 hr periods. 4. Loading the rumen with 1 l. water at 0-1 degree C produced an increment in the duration of infra-red heating obtained in a 1 hr period. At ambient temperatures of 0, 10 and 20 degrees C the increment observed after intraruminal loading with 2 l. water at 0-1 degree C was almost exactly double that obtained with a 1 l. loading. 5. Loading the rumen with 1 l. water at 0-1 degree C did not result in the sheep increasing the duration of infra-red heating obtained at ambient temperatures of 30 degrees C but a 2 l. loading was effective. At an ambient temperature of 40 degrees C the 2 l. load was ineffective.