Reflex onset of polypnoea in sheep

Measurements have been made of the cardio-respiratory activities, ear and lumbar skin temperatures, and temperature of the blood in the carotid artery and jugular vein of partially shorn and unshorn sheep during mammary heating at ambient temperatures of 20/55, 15/55 and 10/55 (dry bulb temperature, degrees C/relative humidity,%).2. Heating the mammary region resulted in a marked rise in respiratory and heart rates of unshorn sheep, whereas, in partially shorn sheep, the heart rates increased without being accompanied by a similar rise in respiratory rates.3. With decrease in ambient temperature from 20 to 10 degrees C, there was a decrease in respiratory response of unshorn sheep during mammary heat treatment suggesting that the magnitude of respiratory response during mammary heat treatment depends on the environmental temperature to which the sheep is exposed.4. The carotid blood temperature declined following mammary heat treatment at all ambient temperatures studied, both in unshorn and partially shorn sheep, but the magnitude of decline was greater in unshorn than in partially shorn sheep.5. The rise in respiratory rates following mammary heating of unshorn sheep at all ambient temperatures, in spite of a decline in carotid blood temperature and the absence of similar responses during flank heating, is attributed to the stimulation of warm receptors in the mammary region.