Thermal panting and respiratory alkalosis in the laying hen

1. Changes in respiratory rate (f), rectal temperature (Tr) and blood acid-base values were measured in laying hens exposed to ambient temperatures (Ta) of 32, 35, 38 or 41 degrees C. 2. At Ta 32 degrees C there was no panting. At Ta 35 degrees C panting occurred without any increase in Tr but there was a slight alkalosis (pH 7.55). 3. At Ta 38 degrees C Tr increased and panting was accompanied by moderate alkalosis (pH 7.58). 4. At Ta 41 degrees C Tr increased considerably and severe alkalosis developed (pH 7.65). 5. From the relation between Tr, f and pH it is concluded that some degree of alkalosis is a normal response to panting in the laying hen.