A pilot study conducted at the University of Helsinki found that high rein tension is associated with mouth opening in trotters, indicating pain or discomfort in the mouth.
Rein tension indicates the force that the rider or driver uses through the reins. It can be measured with a sensor attached between the bit and the rein.
“Our group has previously examined mouth injuries in trotters and we found that moderate and severe injuries were associated with certain bit types. It is possible that drivers eventually started using these bit types because of problems with lighter reins. This is why we wanted to investigate rein tension” , says researcher and veterinarian Kati Tuomola from the Faculty of Veterinary Medicine at the University of Helsinki.
Eight horses and their drivers were recruited for the study. While the drivers walked their horses at a walk and trot on a racetrack, the researchers measured rein tension and recorded video of the horses’ behavior from a moving vehicle. Each horse was equipped with a regular single-jointed bit. A researcher then coded the horse’s behavior from the videos according to a predetermined behavioral catalog. The coder was unaware of any findings related to rein tension and oral injuries in these horses
None of the horses had oral injuries before riding. After the ride, three horses had moderate bruises in their mouths. Their mean rein tension was numerically higher (approximately 3.5 kg per rein) than that of uninjured horses (approximately 2 kg per rein), and they exhibited longer periods of hurried gait.
The average rein tension for a single rein ranged between 0.5 kg and 3.7 kg, with the highest tension varying between 11 kg and 24 kg. According to the researchers, these rein tensions can be considered quite high, as previous studies have shown that horses avoid tensions of more than 0.6-1 kg. To investigate behavioral differences during different rein tensions, five 30-second periods were visually selected from the rein tension graphs of all horses, representing samples of tension ranging from low to high. At low rein tension, the horses walked mainly and kept their mouths closed most of the time. During periods of higher rein tension, the horses mainly trotted slowly or quickly, keeping their mouth open for longer periods of time.
“Horse trainers should monitor the horse’s oral behavior, arousal state and ability to walk calmly and adjust training accordingly. If the horse holds its mouth wide or open repeatedly, this may indicate avoidant behavior, which means discomfort or pain in the mouth. walking may indicate high levels of arousal, which in turn may increase the risk of oral injury,” said Tuomola, lead author of the paper.
