High tension in the reins was linked to trotters opening their mouths, a sign of potential pain or discomfort in the mouth.
A study conducted at the University of Helsinki discovered that high rein tension correlates with trotters exhibiting mouth-opening behavior, which may signal pain or discomfort.
Rein tension refers to the pressure exerted by the rider or driver through the reins and can be quantified using a sensor placed between the bit and the rein.
“Our previous research on mouth injuries in trotters revealed that both moderate and severe injuries were linked to certain types of bits. Drivers might have opted for these particular bits in response to difficulties with lighter rein signals. Therefore, we aimed to investigate rein tension further,” explains Kati Tuomola, a researcher and veterinarian from the Faculty of Veterinary Medicine at the University of Helsinki.
The study involved eight horses along with their drivers. As the drivers steered their horses on a racetrack at both a walk and trot, the researchers recorded the rein tension and filmed the horses’ behavior from a moving vehicle. Each horse was fitted with a standard single-jointed bit. A researcher later analyzed the videos, documenting the horses’ behavior based on a set list of behaviors, without knowledge of prior findings related to rein tension and mouth injuries.
Initially, none of the horses had mouth injuries. However, post-driving assessments revealed that three horses had developed moderate bruising in their mouths. These horses exhibited a higher average rein tension (around 3.5 kg per rein) compared to those without injuries (approximately 2 kg per rein) and demonstrated extended periods of hurried walking.
The average tension for each rein ranged from 0.5 kg to 3.7 kg, with peak tensions hitting between 11 kg and 24 kg. The researchers consider these tensions to be relatively excessive since earlier studies indicated that horses typically avoid tension beyond 0.6-1 kg. To explore behavior variations at different rein tension levels, the researchers selected five 30-second segments from the rein tension graphs of all horses, showcasing a range from low to high tensions. When rein tension was low, horses primarily walked and kept their mouths largely closed. In contrast, during higher tension periods, horses tended to trot either at a slow or fast pace and kept their mouths open for longer durations.
“Trainers should pay attention to how horses behave with their mouths, their level of arousal, and their ability to walk calmly, adjusting training practices as needed. If a horse frequently keeps its mouth wide open, it could signify discomfort or pain. Additionally, hurried walking may indicate heightened arousal, which could increase the likelihood of mouth injuries,” advises Tuomola, the lead author of the study.
