What if Horses Were Humans? Comparing Rein Tension and Bit Pressures to Human Pressure Pain Thresholds

Bit pressure and rein tension-induced mouth pain in horses have recently become a significant welfare concern, fueling debates within the equestrian community and beyond. Evidence indicates that bits can cause pain-related behaviors and even oral lesions. Although studying pressure-induced pain in animals is challenging, the similarities in the physiology of pain processing (nociception) across mammals suggest that it is reasonable to assume that pain perception in humans and horses is principally comparable. Therefore, we compared human pressure pain detection thresholds (PPDTs) to reported rein pressures in equestrian sports as reported in the scientific literature. Reported rein tensions (kPa) range from a minimum of 91.2–107.87 to a maximum of 1314.09–4285.51, while human PPDTs (in kPa) are 232.4 for the face, 445.3 for the hand, and 535.5 for the foot. These comparisons reveal that only the lowest reported bit pressures would be pain-free for humans. Average to maximum pressures would cause strong to severe pain sensations in humans. Furthermore, data on pressure pain-induced stimulus response functions suggest that bit pressures commonly encountered in equestrian sports could cause lesions in humans, making them unacceptable in human experimentation. In conclusion, bit pressures as reported in the scientific literature would cause significant pain if applied to humans, raising welfare concerns for horses.