Thermal response of intravascular and rectal tissue to temperature changes and chemical conditions in the rumen of sheep.

1. Experiments were conducted with two wether sheep which were fitted with rumen cannulae and chronically implanted intravascular thermocouples. An attempt was made to study the thermal response of intravascular and rectal tissue to temperature changes and chemical conditions in the rumen.2. When ice or hot water were placed in the rumen there was an immediate fall or rise in the intravascular temperature accompanied by a similar change in rectal temperature. The intravascular temperatures returned to their precooling or preheating level of 40 degrees C within 130 min, the rectal temperatures required 6-8 hr to return to their pretreatment values.3. When 0.5 M acetic acid was infused into the rumen there was a marked rise in the intravascular temperature, over and above the diurnal rhythm but not in rectal temperatures. Infusion of mixtures of acetic plus propionic or acetic plus n-butyric acids caused an intravascular temperature rise on feeding within the range of the diurnal pattern. In fasted animals, infusions of volatile fatty acids resulted in no rise in intravascular temperature.