Effect of low and medium environmental temperatures on physiological and reproductive parameters in Soay rams

Abstract

Seven adult Soay rams, which had been cranially sympathectomised, were used to study the effect of a low (7°C) and medium (15°C) environmental temperature on three physiological parameters (body temperature, heart rate and respiration rate) and two reproductive parameters (testis diameter and plasma testosterone concentration). They were kept in a controlled temperature room with artificial lighting conditions of eight hours light and 16 hours dark (8L:16D). There was a short adaptation period, followed by three weeks at 7°C and three weeks at 1^°C. Adequate food and water was present at all times.

Results showed that body temperature was lower during the 7°C period than the 15°C period (P < 0.05). All the other results were not significant but certain trends were noticed. The heart rate was greater during the cool period compared with the warmer period; and the respiration rate was higher during the warm period. The testis diameter increased from the beginning of the 7°C period to reach a maximum size at the end of the initial period; at the higher temperature (15°C) testis diameter gradually decreased. Testosterone concentrations were high throughout the whole experimental period but the levels were greater during the 15°C period compared with the 7°0 period. It was concluded that although light acts as the major stimulus to the onset of the breeding season in rams, low temperature alone plays a significant role, and the maximum effect is due to a combination of the two factors.