The activities carried out by the horses are repeated with a certain periodicity. However, animals do not have clocks to measure time like us.
Instead, your body has an internal natural clock, capable of adjusting the functioning of the body at different times of the day and at different seasons of the year.
This internal clock of the horses allows to regulate, for example, the cycles of sleep and wakefulness, or the arrival of the heat in a certain date of the year. The main element that the horse’s organism uses to keep its clock “on time” is the light and its variation between day and night. In addition to regulating rest intervals, the light cycle is used to adjust other functions. Stallions, for example, secrete a greater amount of testosterone, the male hormone, during the day than at night.
In addition to the cycles of light and darkness there are other environmental factors, such as temperature or atmospheric pressure, which influence the biological rhythms of the horse.
The control of circadian rhythms is carried out by two structures of the central nervous system: the hypothalamus and the pineal gland, the latter producing the hormone melatonin. During the night the pineal gland secretes melatonin, which is responsible for regulating many physiological functions, such as sexual behavior.
When a behavior or a certain physiological activity is repeated every year we say that it follows an annual rhythm and when it does every day we say that it follows a circadian pattern.