How horses see the world: Jump colours need a rethink, say researchers

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A fence at Cheltenham racecourse on an overcast day, showing the human view above and predicted horse vision below. The images illustrate the much higher contrast of white, fluorescent yellow, and blue (in the colour boards) to the fence and its surroundings than the orange takeoff board and midrail. Photos: https://doi.org/10.1016/j.applanim.2019.104882

Orange may be the new black in the world of television, but it seems the colour has no place in jumping obstacles for horses.

The colour has received the thumbs down from researchers Sarah Catherine Paul and Martin Stevens, who explored horse vision and the visibility of jumps in horse racing.

The pair say there is a need to understand how horses see and respond to obstacles, predominantly fences and hurdles, as this has implications for horse and rider safety.

“However, obstacle appearance is currently designed to human perception.”

Their findings on colour have application further afield, in showjumping.

While orange is conspicuous to humans with their trichromatic vision, this is not the case for horses, with their dichromatic colour vision.

“This means that they have reduced colour vision compared to humans, seeing colours along a continuous range from blue to yellow, and therefore cannot distinguish between many of the colours that humans see as red, orange, and green, unless they also differ in brightness,” the pair say.

“The orange fence markers used in racing may therefore increase the visibility of fences against the background to a far lesser extent for horses than for humans.”

With that in mind, the pair set out to examine the conspicuousness of current markers to horses in jumps racing.

They analysed the contrast of traditional orange markers currently used on fences from 11 British racecourses, and compared this to potential alternative colours, while also investigating the effect of light and weather conditions on contrast.

For their work, 14 horses were trialed over a pair of jumps that differed only in the colour of the takeoff board and midrail. Each horse was jumped over a pair of fences three times. All trials were filmed and the jumping efforts analysed.

“Fence colour significantly affected the way a horse jumped the fence with regards to its takeoff and landing distances, and the angle of takeoff that a horse made during a jump,” the pair reported in the journal, Applied Animal Behaviour Science.

They found that using white, fluorescent yellow, or bright blue for fence markers would provide higher contrast for horses than the traditionally used orange markers.

They said contrast was maximised across light and weather conditions by highly luminant whites or blues at the base of the fence — the take-off board — in jumps racing.

Further, fluorescent yellow was found to have the greatest contrast against the main fence body (that is, when used for midrail colouring).

Horses, they found, jumped differently over white, fluorescent yellow, and bright blue marked fences compared to orange-marked fences.

“We found that, for horses, orange has poor visibility and contrast against most surroundings.

“In comparison, yellow, blue, and white are more conspicuous, with the degree of relative contrast varying with vegetation or background type.

“Results were mostly consistent under different weather conditions and time of day, except for comparisons with the foreground turf in shade. We then tested the jump responses of racehorses to fences with orange, fluorescent yellow, bright blue, or white takeoff boards and midrails.

“Fence colour influenced both the angle of the jump and the distances jumped.”

Bright blue produced a larger angle of takeoff, and jumps over fluorescent yellow fences had shorter landing distances compared to orange, with bright blue fences driving a similar but non-significant trend.

White, they found, was the only colour that influenced takeoff distances, with horses jumping over white fences having a larger takeoff distance.

Photos of all four colours of experimental fence used in the behavioural trials, on the left in human (jockey) vision and on the right in predicted horse vision. Fence colours are from top to bottom orange (traditional), white, fluorescent yellow, and bright blue. Photos: https://doi.org/10.1016/j.applanim.2019.104882

“Overall,” they wrote, “our results show that current obstacle coloration does not maximise contrast for horse vision, and that alternative colours may improve visibility and alter behavioural responses, with the ultimate goal of improving safety and welfare.”

“The use of white, yellow, or blue would significantly improve the visibility of the takeoff board, midrail, and top of the fence/hurdle to horses.

“However, it is important to note that the exact shade, texture, and/or brightness properties of the white, yellow, or blue used influences the conspicuousness of these colours and that the suitability of each colour depends on the part of the fence in question.

“Light blues provide higher luminance contrast than darker blues, but blues and whites may blend in with the sky if used on the top of a fence with no treeline behind it.

“The choice of yellow is also key, as matt fluorescent yellow consistently has the highest colour and luminance contrast of all the colours tested, whereas non-fluorescent shades are far less distinguishable from foreground turf, or other bright green vegetation.”

This, they say, is particularly important when considering the takeoff board, where a fluorescent yellow board would provide markedly improved contrast against the foreground, but a non-fluorescent shade of yellow would have similar contrast to both light green and the current orange colour used.

“Therefore, if fluorescent yellow cannot be sourced or is not financially viable to use on a large scale across an entire racecourse, white or light blue would be a more suitable alternative than non-fluorescent yellow.”

The pair, with the Centre for Ecology and Conservation at the University of Exeter, said there was a significant effect of weather/light conditions on the contrast of white, blue, yellow, and current fence components.

“Our study shows that the current colours used as visibility features on fences and hurdles in UK horseracing are unlikely to be well designed to horse vision.

“In fact, several other colours would likely provide much greater visibility to horses and induce potentially beneficial behavioural responses.

“Nonetheless, there are other factors to consider besides direct visibility in the choice of obstacle colour.

“For example, lots of other features exist in the racecourse environment that are white (e.g. railings), meaning that white may potentially be confused with other objects in the visual scene.

“Otherwise, yellow is highly effective in all comparisons except under strong shadows, and these tend to occur at the base of fences, where yellow offers less of a visibility advantage over blue or white.

“Therefore, blue or white may be a better choice for features close to the ground.”

The downside of white, however, is that it may quickly become dirty, reducing its effect.

“As such, optimal fence design for horse vision may involve orange colours being replaced with a highly fluorescent white (or a light, highly luminant blue) for the takeoff board, and a fluorescent yellow for the midrail and for hurdles.”

Horse vision and obstacle visibility in horseracing
Sarah Catherine Paul and MartinStevens
Applied Animal Behaviour Science, Volume 222, January 2020, 104882,
https://doi.org/10.1016/j.applanim.2019.104882

The study, published under a Creative Commons License, can be read here

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