| Abstract: | Rectal temperature of 10 female adult horses was recorded every 2 h for 10 consecutive days under a natural winter photoperiod (9 h of light and 15 h of darkness per day). A robust daily rhythm of body temperature was observed in all animals. The rhythm had a mean level of 38.3°C and a range of excursion of 1.0°C. Temperature started its daily ascent at dawn each day and reached a maximum 14 hours later. Body temperature of 5 of the horses was studied for 10 more days under constant illumination. The rhythm persisted under this condition, although with a slightly longer period of 24.2 h, which confirms the endogenous nature of the rhythm. Despite the fact that the body size of the horse is several orders of magnitude greater than that of rodents, the various parameters of the body temperature rhythm of the horse are similar to those of several species of rodents previously studied. |
