The Effect of Two Different Bits on Tensile Forces in Side Reins

Introduction The effect of bits on the mouth of the horse is a source of controversy in animal welfare discussions. The goal of this study was to determine the influence of two different bits on tensile forces in side reins applied to exercising horses. Methods Ten Warmblood horses (2 mares, 8 geldings; mean age: 12.4 ± 5.3 years) were assessed during walk and trot on a treadmill. Side reins were used to position the horse's head so that the nose was nearly vertical. Two different bits were utilised: a double jointed snaffle (bit 1) and a mullen mouth snaffle (bit 2). Rein forces were measured with an electronic sensor based on a force sensing resistor (27 g, sample rate 120 Hz, Interlink Electronics corp.), synchronized with a kinematic system (10 cameras, 120 Hz, Motion Analysis corp.). The force sensors were calibrated with masses of 1 Kg (=9.81 N) and 4 Kg (=39.24 N). Statistical analysis was performed using the software SPSS. Normality of data was checked with the Kolmogorov-Smirnov-test and data were analysed with repeated measures ANOVA (P<0.05). Results Maximum tensile forces differed significantly between the two bits. Maximum forces at walk were 16 ± 1.9 N using bit 1 and 15.7 ± 1.9 N using bit 2. At trot the forces (12.7 ± 2.0 N bit 1; 10.4 ± 1.8 N bit 2) were significantly reduced compared to walk. There was no significant difference between left and right rein forces. Conclusions The type of bit has an effect on the tensile forces in the side reins and hence on the forces exerted on the mouth of the horse. Ethical Animal Research This study was approved by the local ethics commission. Sources of funding: University of Veterinary Medicine of Vienna. Competing interests: none.