EN
The objective of the study was to determine the activity of the sympathetic and parasympathetic systems associated with various kinds of behaviour in Thoroughbred yearlings during initial training by natural methods. The initial training lasted approximately one hour a day for three successive days. Each day, the behaviour of each colt during the first 15 minutes of training was filmed. During training, a telemetric device was used to measure heart rhythm parameters: heart rate (HR per minute), which shows the activity level of the sympathetic system, and RMSSD (root mean square of two successive RR intervals in QRS curve; ms), illustrating the activity level of the parasympathetic system. On the basis of the film, the frequency of 10 most typical kinds of behaviour was estimated. The synchronization of the film with the heart rhythm parameters record made it possible to determine the mean values of these parameters for particular kinds of behaviour. The results show that on the successive days of training, the activity of the parasympathetic part of the autonomic system increased, and the frequency of reactions decreased. The heart rhythm parameters show that, among the typical reactions to training, four kinds of behaviour are desirable: turning the head towards the trainer, low position of the head, turning ears towards the trainer and licking the lips. Other kinds of behaviour, that is, running away, a high position of the head, vocalization, teeth grinding, tail movements to the sides and defecation, are undesirable. The highest excitability is associated with running away and a high position of the head, whereas the head turned towards the trainer and a low position of the head show that the horse is calm.