The Impact of Bits on Equine Welfare, Part 2
Rein Tension
In a study investigating the rider effects on horses (Christensen et al., 2021) found that the overall level of rein tension for the 96 rider & horse pairs was 26.9 ± 0.6N for the right rein (3.01 kg) and 27.4 ± 0.6 N left rein (2.79kg). There was a significant effect of the rider on the rein tension level. Some of the riders applied significantly more rein tension than others, when riding the same 10 horses through the same dressage test.
When looking into ridden and unridden rein tension, a study found that the mean maximum ridden rein tension was significantly higher than non-ridden tension. The results showed that the mean maximum ridden rein tension was 24.0 N ± 12.3 N (2.44 kg) (Piccolo & Kienapfel, 2019), similar to the results found in the above study.
This study also looked into the effect of the rein tension on conflict behaviours. It found that without a rider, 7 out of the 13 horses showed conflict behaviours compared to 11 of 13 when with a rider. It was also noted that tail swishing and unusual oral behaviour was more frequently seen in the ridden horses than unridden.
In a study investigating rein tension at onset and end of oral behaviours and head movements in unridden horses (Eisersiö et al., 2023) found that horses attempted a range of behaviours to evade rein tension. There was a decrease in average rein tension (sum of left and right rein) from onset of the rein tension applied to end with the following behaviours:
- Open mouth (from 19 to 11 Newtons (N)
- Biting on the bit (from 11 to 5 N)
- Head upward (from 16 to 12 N)
While there was an increase in rein tension associated with head forward (from 27 to 37 N) and head downward (from 17 to 46 N). The results suggest that horses will open their mouth, or bite on the bit, to alleviate the oral tissues from pressure; move the head upward to avoid rein tension and move the head forward or downward to increase rein tension, likely in a presumed attempt to break free from the pressure applied.
When looking at voluntary rein tension in young, untrained horses, a study had some interesting results. The objective was to investigate how much rein tension young inexperienced horses are willing to accept in order to obtain a food reward, over three consecutive test days (CHRISTENSEN et al., 2011). Fifteen 2-year-old horses, that were new to the bridle, were encouraged to stretch their head forward over a bar, in order to obtain a food reward. The horses were exposed to three tests:
- Two control tests of loose Reins
- Intermediate rein
- Short rein
The results showed that the horses applied significantly more tension on the first day of the testing, an average of 10.2N (1.04kg) compared to day two (6.0N) 600g and day three (3.7N) 370g. The horses also showed more conflict behaviours when on the short rein test. From this study it was concluded that the horses learned to avoid the tension rather than habituate to it.
Similar results were also reported in a study looking at rein tension in unridden horses (Kau et al., 2020). Horses were equipped with either a double jointed snaffle (DJS) or a mullen mouth snaffle (MMS) with a loose ring, attached to a roller with side reins and exercised on a treadmill. The mean maximum force for the DJS at walk was 7.85N on the left rein and 8.98 N on the right rein, while the MMS was 6.65N for the left rein and 7.89N for the right rein. This shows a range of the maximum force allowed by the horses at without a rider to be 6.65 – 8.98N (664-898g). The researchers concluded from the study that side rein tension forces do not correspond to the forces found during riding and that the DJS exhibited a higher side rein tension, indicating higher bit contact.
When looking at rein tension in double bridles vrs snaffles, an unpublished study (Marlin et al., 2024) has reported that total force applied by the rider for the double bridle (curb and bridoon) was lower than the snaffle bridle (44.9N vrs 53.7N) It was also noted that the total force was lower for the curb bit (CB) than bridoon bit (BB) in all gaits:
- Walk- CB: 9.6N, BB: 20.7N
- Trot- CB: 19.1N, BB: 26.4N
- Canter- CB: 20.5N, BB: 39.8N
From these studies, we can gather that the voluntary rein tension horses have shown to accept ranges from 370g to 1 kg. However, ridden rein tensions far exceed this, with up to 5.3kg of applied rein tension by riders.
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