Further observations on the scrotal skin temperature of the bull, with some remarks on the intra-testicular temperature

Abstract

1. The temperature of the scrotal surface has been recorded at various air-temperatures within the range 10°C. to 40°C. (50°F. to 104°F.). 2. At low air-temperatures (10°C. to 25°C.) the temperature on areas I, II, and III gave a mean value of 32.0°C., 31.0°C., and 33.0°C.; at high air-temperatures (25°C. to 40°C.) the same areas were 33.9°C., 33.8°C., and 36.7°C. 3. Readings (28) of the skin-temperature underneath the hairy coat, taken simultaneously, gave mean values of 33.6°C. at low air-temperatures and 36.5°C. at high air-temperatures. 4. The mean body-temperature at which the high temperature group readings (15) were taken was 38.6°C. 5. Scrotal temperatures at areas I and II increased almost similarly with increasing air-temperature, i .e. slow increase at low air-temperatures (0.06°C. and 0.09°C. per 1° air-temperature increase) and more rapid increase at high air-temperatures (0.29°C. and 0.26°C. per 1° air-temperature increase). Scrotal temperatures of area III and skin-temperatures increased similarly with increasing air-temperature over the whole range of 10°C. to 40°C. air-temperature. The rate of increase for scrotal area III was 0.43°C. at 10°C. air-temperature, and 0.11°C. at 40°C. air-temperature. The rate of increase in the skin was 0.56°C. at 10°C. air-temperature, and 0.14°C. at 40°C. air-temperature. 6. The degree of contraction and relaxation of the scrotum, as indicated by its length from the dorsal to the ventral extremity, gave a mean value of 24.2 cm. at low air-temperatures and 29.0 cm. at high air-temperatures, a difference of 4.8 cm. 7. From limited observations on the body-temperature, at high air-temperatures only, there appears to be a highly significant relationship between the body-temperature and that o£ the air and scrotal areas I, II, and III. There was no significant relationship between body and skin-temperature. 8. An observation was carried out at artificially created low air-temperatures. The bull was exposed to a temperature of 4°C. to 6°C. for six hours. 9. Under these conditions scrotal area I increased immediately from 30°C. to 33°C. It then decreased and fluctuated between 31°C. and 32°C. During the following 4 hours, scrotal area II always showed lower temperatures than area I (up to 3°C.) . Scrotal area III increased markedly at the beginning and then showed a slight tendency to decrease, but after one-and-a-half hours remained 2°C. to 4°C. lower than skin-temperature. 10. There was marked shivering, which began one-and-a-half hours after exposure, and continued until one-and-a-half hours after the bull was removed from the cooling chamber. 11. The pulse rate per minute varied from 66 to 62 in the cooling chamber and dropped from 64 to 58 within an hour after removal. 12. The respiration count was 16 per minute after six hours exposure and 13 per minute one hour after removal. · 13. The skin-temperature showed steady increase, up to 35°C. (air-temperature 4°C.). It then decreased continually to 32.6°C. at the end of the experiment, but a constant level had apparently not been reached. After removal from the cooling chamber, there was an increase of 3°C. within an hour. 14. The length of the scrotum decreased with a fall of scrotal and skin-temperature during exposure. There was marked relaxation upon removal to higher air-temperature. 15. The body-temperature increased by 1°C. at the commencement of exposure, and remained remarkably constant at about 39°C. throughout the exposure and after removal from the cooling chamber. 16. The intra-testicular temperature, measured with a thermo-needle, at an air temperature range of 15·2° C. to 37·8° C. remained within a narrow range, between 34.8°C. to 37°C. for the left testicle and 34.7°C. to 36.6°C. for the right testicle. 17. Artificial displacement of the testicle to close contact with the body resulted in an increased intra-testicular temperature of 2.5°C. and a decrease in the temperature of the scrotal area not overlying the testicle, of 6.0°C. and 3.2°C. The scrotal surface over the displaced testicle also increased considerably to 37.0°C. 18. The heat regulating mechanism of the scrotum is extraordinarily efficient in maintaining the testicular and scrotal surface-temperatures within a very narrow range at air-temperatures between 10°C. and 40°C. It is suggested that this efficiency is not purely physical, due to the action of air temperature on the contracted or relaxed scrotum. This suggestion is strengthened by the fact that scrotal areas I and II, in close contact with the testicle, behaved similarly but differently -to scrotal area III and the skin. It appears probable that vascular reaction accompanies scrotal contraction and relaxation. 19. The scrotal temperature reaction over that portion of the scrotum removed from close testicular contact, is extraordinary in that there was a very marked decrease in temperature to 28.2°C., i.e. 3.8°C. lower than air-temperature, and 8.8°C. lower than intra-testicular temperature (average for points 1 and 2). It is suggested that this reaction was an attempt by the temperature regulating mechanism of the scrotum to maintain the testicular temperature, which was raised by contact with the body , at the normal temperature for prevailing air-temperature.