Mirror, Mirror, on the Wall

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An inexpensive acrylic mirror installed in a horse’s box stall significantly reduces weaving and nodding, according to new research from the United Kingdom. The study, led by animal scientist Daniel Mills of the University of Lincoln in Lincolnshire, also contributed several observations about weaving and its possible sources.

For starters, data from the work pokes holes in the theory that horses learn to weave by watching other horses weave. “If a weaver has a mirror and weaves near it, you would expect that to stimulate further weaving, if copy-cat behavior is involved,” Mills said. But this did not happen. Instead, known weavers that were provided a mirror in their stalls weaved significantly less.

“Therefore, we conclude that it is more likely that horses within a yard [barn] develop similar stereotypies because they are subject to the same management practices,” he said, such as long periods of confinement and too much highly concentrated feeds.

“Both studies found that horses provided with mirrors weaved significantly less than horses without mirrors.”

According to Mills, more than 15 percent of domesticated horses engage in some sort of stereotypy, such as weaving. The habit is believed to cause uneven muscular development in the neck, weight loss and fatigue, which can affect the horse’s performance

A common treatment for weaving is to install “weaving bars” on either side of the stall door, so that the horse cannot move back and forth by the door. A weaver, however, often responds to the bars by standing back further from the door in order to weave.

Another study showed that installing a grilled window into an adjacent stall reduced weaving. But since not everyone can cut holes in their horse’s stall, and providing adequate turn-out is often difficult at crowded stables, many barns need an alternative treatment.

Mills and his colleagues got the idea to try mirrors from another researcher, who suggested a mirror might mimic social contact with other horses and so reduce the incidence of weaving.

To study the effect of mirrors, the researchers conducted two studies. In one, they observed the behavior of six known weavers over one week. In the second, they observed another six known weavers over twelve weeks. Both studies found that horses provided with mirrors weaved significantly less than horses without mirrors. Some weavers didn’t weave at all with the mirror in their stall.

In the second study, six horses were kept in a variety of stall situations, from large, isolated box stalls with no contact with other horses to smaller stalls at the entrance to the barn, from which the horses could routinely observe the activities in and out of the barn. And all horses spent time with and without mirrors.

Observers recorded the horses’ behavior every day during the study and recorded position and activity in the stall, including weaving and head-nodding.

Overall, 28 percent of observations of horses with mirrors recorded the animals oriented toward the mirror, and not weaving. “There was also a decrease in other potentially undesirable behaviors, namely head nodding and head threats,” or laying the ears back and extending the neck, Mills said. He noted that this finding “may be particularly worthy of further investigation.

“...weaving is the result of anticipation.”

“Both stereotypy and aggression are believed to be a common consequence of frustration in the horse and other species,” he said. “So these effects may be the consequence of relief of frustration.”

The study also provides support for the theory that weaving is the result of anticipation. Throughout the study, horses that weaved engaged in the behavior primarily in the mid-morning and late-afternoon periods—times that preceded feeding or turnout. The researchers saw significantly less weaving in the early afternoon, when there was little disturbance of the horses. This contradicts an alternative theory, that weaving is an expression of boredom.

A mirror in a weaving horse’s stall may reduce the stereotypic behavior by mimicking visual contact with other horses and thereby minimizing social isolation, Mills said. But he noted that since horses with a clear view of other horses still weave, this cannot be the only factor.

“It could be the perceived proximity and/or activity of the social companion that is important,” he said. “Alternatively, the mirror may have acted as an environmental distraction.” When the study horses had the mirrors in their stalls, they spent more time facing the mirrors than they did with their heads over the stall doors, where most weaving occurs.

The short story is that whether it’s a change in the stall’s environment or a perceived companion, horses with the mirrors did respond to the experiment, which could be just the trick for many stabled horses.

McAfee, Lynn M, Daniel S. Mills and Jonathan J. Cooper. The use of mirrors for the control of stereotypic weaving behaviour in the stabled horse. Applied Animal Behaviour Science (in press).