Abstract
Three castrated pigs with initial body weights of 45-48kg were exposed to extremely high temperatures in a room with controlled temperature so as to investigate the effects of severe thermal stress upon swine, by raising the temperature as time elapsed. On pig was exposed to a temperature ranging from 33 up to 37°C for 3.5 days, while another pig was exposed to a temperature in a range identical as above, but was exposed to a higher temperature up to 49°C thereafter for a total period of 4.5 days and the third pig was exposed to the temperature ranging from 23.9 to 33.7°C for 6 days on outdoor and then to abrupt rise in the ambient temperature by more than 10°C and eventually to 41°C for 4 hours. The heart rate, respiratory rate and rectal temperature were measured for all the three pigs. All of these physiological responses were intensified as the temperature was gradually elevated. The heart rate definitely increased at a temperature above 41°C. The rises in the respiratory rate and rectal temperature were found to be in an even closer relationship to the temperature than the heart rate. The rates of intensification of these physiological reactions were mild up to approx. 40°C if the temperature was elevated gradually. Their maximum values were observed in the third pig at 41°C, where the heart rate, respiratory rate and rectal temperature were 130/min, 230/min and 42.8°C, respctively. Also in the second pig, a rectal temperature of 42.8°C could be observed at a temperature of 49°C. The maximum values of the respiratory rate observed in the present study were higher than those so far reported at temperature of 32-34°C. This result revealed that pigs can tolerate at a high temperature even around 40°C by increasing their respiratory rates, and the results of observations on the heart rate and rectal temperature also proved the tolerating ability of pigs.
Taking into consideration that all the three pigs still had considerable tolerability left even when they were evacuated from the room after the measurement, it was conceived that pigs can endure the high temperature which is usually experienced in summer in Japan, if they are to tolerate the only factor of high temperature.
