Chewing wooden objects is a natural behaviour observed in horses. Although they cannot digest wood, it is not uncommon for wild horses to browse or chew on tree bark or branches.

In fact, feces of feral horses has been found to contain traces of bark from different trees. [1] Researchers aren’t sure why horses chew wood in the wild, but speculate they may have a requirement for indigestible roughage.

However, excessive wood chewing in domesticated horses is considered abnormal behavior. Wood chewing is one of several types of stereotypic behaviors or habits that horses can develop.

Stereotypic behaviors, often referred to as stereotypies, are repetitive behavior patterns with no apparent function. [2] They may develop out of boredom or they may be a coping mechanism for stress.

Wood chewing in horses may also develop subsequent to a nutritional deficiency in the diet. Over time, this behavior can have negative effects on the horse, including weight loss, gut issues or oral injuries.

Continue reading to learn why some horses wood chew and how to manage and prevent this unwanted behavior.

Wood Chewing in Horses

When horses chew wood, they usually grasp the top of a horizontal surface (such as a stall door or fence) with their front teeth, break off pieces of wood, and ingest the material. Some horses kept in dry lots or pastures may routinely chew on trees as well.

Though some people confuse wood chewing with cribbing, they are not the same behavior. Cribbing is a behavior in which a horse grasps an object with its incisors, flexes its neck, and swallows air. Interestingly, wood chewing may precede or be associated with cribbing in some horses. [3][4]

Studies suggest that anywhere from 20-35% of all domesticated horses develop a stereotypic behavior of some kind. Wood chewing occurs in about 5-10% of domesticated horses. [5]

Aside from wood chewing and cribbing, other stereotypies include weaving, stall walking, windsucking, pacing, head-bobbing, and self-mutilation.

Causes of Wood Chewing

Stereotypies, such as wood chewing, are usually associated with horses that are managed in an unnatural manner or environment. [2]

These behaviors develop as a coping mechanism to deal with stress related to their management, housing, diet, or lifestyle. [4]

Natural Horse Behavior

Natural equine behavior is primarily comprised of the three following activities:

  1. Avoiding possible danger and escaping from predators (flight response)
  2. Engaging in social contact with other horses
  3. Moving and grazing to consume fiber, which constitutes a significant portion of their day.

By understanding these natural equine behaviors, horse owners can gain insight into the origins of “unwanted” behaviors in their horses. [4]

In the following section, we will examine some of the potential causes of wood chewing behavior in horses, including stall confinement, insufficient long-stem forage in the diet, and a lack of activity.

Management Practices

Husbandry and management practices that restrict natural behaviors are considered the primary risk factors for the development of wood chewing. Some of these practices include:

When horses are stalled full or part-time, their environment restricts their ability to perform species-appropriate foraging behaviors. These natural grazing behaviors may become redirected if adequate forage is not provided in their environment, resulting in wood chewing and other oral stereotypies. [4]

Keeping horses in stalls also reduces their ability to move and interact with other horses, which can lead to increased stress levels. Chronic stress caused by unnatural management practices appears to play a part in the development of stereotypies, such as wood chewing. [3]

Thoroughbreds, commonly utilized in high-performance sports such as horse racing, are frequently managed in stables, which increases their likelihood of developing stereotypies, including wood chewing.

Similarly, stallions, often housed in individual enclosures to prevent accidental breeding and aggression, are also at an elevated risk of developing stereotypies. [2]

Lack of Long-Stem Forage

Horses have evolved to graze on fibrous vegetation throughout the day, and have an and instinctive need to chew and ingest fiber.

The act of chewing serves a purpose beyond just consuming food. When horses chew on long-stem fiber, such as hay or grass, they produce saliva, which then buffers the acid that is continually produced in the stomach.

Research shows that gastric ulcers develop when horses go for long periods of time without eating long-stem fiber from grass or hay.

Free-ranging horses will spend the majority of their day grazing to not only meet their caloric needs, but also their need to ingest fiber. On the other hand, many stalled performance horses are fed a diet high in concentrates and low in forage, sometimes going long periods between meals.

When a horse’s long-stem fiber requirements are not adequately met, or if the horse does not have free-choice access to forage, they may resort to chewing on other objects in an attempt to fulfill their nutritional and behavioral needs. [4] Studies suggest that even if concentrates are provided to meet a horse’s nutrient requirements, the horse’s motivation to forage often remains. [3]

Researchers have also noted that some horses on green, lush pastures in spring may chew bark or wood fences. At this time of year, the sugar content of grasses is higher and the fiber content is lower. Wood chewing in this instance may be explained by reduced roughage content in the pasture grasses. [6][4]

Concentrates

Research indicates that horses being fed concentrates more than twice a day are at a higher risk of developing wood chewing behavior or other stereotypies. [7]

When calorie-dense commercial feeds are provided, horses consume their dietary requirements in a much shorter period of time than if they are allowed to graze or eat hay continuously throughout the day. [8]

A study demonstrated that horses fed a hay-based diet dedicated 40% of their time to eating and 45% of their time standing in the stall. In contrast, horses fed a concentrate diet allocated only 3% of their time to eating and 62% of their time standing. [8]

This can result in more time between meals with no forage available and nothing to keep the horse occupied.

Other possible consequences of feeding large, grain-based meals are abdominal discomfort, colic, and gastric ulcers. Large meals can overwhelm the stomach and small intestine while also increasing the transit rate of food moving through the GI system. [3]

Starch overload occurs when undigested starches reach and are fermented in the hindgut, leading to disturbances in the microbial population, as well as a drop in pH levels. [3]

Abdominal discomfort associated with large grain meals has been linked to abnormal oral behaviors in horses. [3]

High concentrate or pelleted diets can also increase the incidence of wood chewing. [8]

Boredom and Lack of Exercise

Boredom may also play a part in wood chewing. Studies show that horses receiving exercise spent less time chewing wood. In one study, exercise reduced oral contact with stall surfaces, possibly by providing environmental enrichment. [9]

Researchers have observed that wood chewing behavior in horses peaks between 10 PM and midnight. Additionally, horses engage in more wood chewing during cold and wet weather, especially when they are confined indoors and have less activity in their day. [1]

Early Weaning

Early weaning is recognized as a significant contributor to the development of stereotypic behaviors in horses.

In one study, approximately 10% of foals began cribbing and 30% showed excessive wood chewing after weaning. Most of these foals were weaned between the age of 4-6 months. [10]

Keeping foals with their dams for a longer period of time may decrease the occurrence of stereotypic behaviors in both foals and mares. [10]

Copycat Behavior

Limited research suggests that exposure to other horses that chew wood may also be a risk factor in developing the habit.

Having other horses within sight is generally beneficial for reducing stress in stabled horses. However, a study revealed that the presence of a neighboring horse displaying stereotypic behavior significantly increased the likelihood of a horse developing the same behavior. [7]

It remains uncertain whether the increased risk of stereotypies is due to mimicry, where horses copy the behavior of their peers, or if it is influenced by similar management factors that exist in the shared environment.

Researchers have also observed that stereotypies tend to be more prevalent in barns where there is increased general activity among horses. Constant stimulation from nearby horses engaging in weaving, stall walking, cribbing or wood chewing might lead to stress and induce similar behaviors in their equine neighbors. [7]

Consequences of Wood Chewing

Not only does wood chewing damage fences and stalls, it can also be harmful to the horse’s health and performance. Wood chewing is associated with conditions such as gastric ulcers, colic, tooth wear, weight loss, and poor body condition. [7]

Ingestion of splinters might also lead to oral wounds, a puncture in the gastrointestinal system, or stimulate enterolith formation. Horses are also at risk of injuring themselves on damaged structures within their barn or turnout environment.

In addition, certain types of trees, wood, paints, and wood stains can be toxic to horses if ingested. Excessive wood chewing, in some cases, can even result in impaction colic, a condition where the digestive system becomes blocked. [6]

Treatment for Wood Chewing

Once the behavior is established, it may not be easy to stop your horse from wood chewing. However, there are several measures you can take to reduce or possibly eliminate the habit.

Management Changes

The first step to resolving wood chewing in horses is to evaluate their management and consider changes that address the underlying cause of the stereotypy.

Stereotypies are strongly associated with environmental deficits. Improving the horse’s environment and management is preferable to other efforts to curb the unwanted behavior. [4]

Every horse needs a supportive and stimulating environment that enables the expression of species-appropriate behaviors, including grazing and freedom of movement.

Furthermore, horses should be provided with appropriate exercise and regular turnout with other horses to promote physical and mental well-being. Minimizing the amount of time your horse spends confined in a stall can help reduce stereotypic behaviors.

Using chopped straw as stall bedding may also help to eliminate wood chewing behavior. Horses tend to spend more time eating straw, a natural forage, compared to other types of bedding.

However, there is a small risk of impaction colic after changing to straw bedding, especially if no other sources of fiber are available to the horse. [2]

Feeding Changes

One of the best ways to prevent or minimize wood chewing is to feed higher quantities of long-stem grass hay. Horses with more fiber in the diet are less likely to exhibit wood-chewing behavior. [6]

Increasing your horse’s access to hay enables them to engage in more natural grazing behaviors. [5/4] Research also shows that horses eating hay spend four times more chewing per day than those fed a pelleted diet.

Ideally, provide free-choice access to forage using a hay net or slow feeder, as needed, to regulate intake. Feeding a variety of forage types may also help to prolong meal time and enrich your horse’s foraging behavior. [3]

If feeding more forage isn’t possible, consider using a device that will dispense high-fiber feed (i.e. hay cubes or forage pellets) throughout the day. This will increase time spent foraging and reduce inactive time spent in the stall. [4]

Wood Chewing Deterrents

If you have made management changes but the horse continues to wood chew, you may need to explore other options, such as chew-stop formulas or structural changes to your stalls and fences.

Capsaicin, derived from chili peppers, can be applied to wood surfaces that horses may be inclined to chew, acting as a deterrent. [5] Capsaicin can serve as a natural repellent due to its irritating effect on the nasal and oral areas.

When using any form of topical deterrent, ensure that it is not toxic to horses.

Metal panels can be used in place of wooden boards in your horse’s enclosures. You can also protect wood ledges and corners with angle iron or other metal edging.

Alternatively, electric fence wire can be used on top of boards or wood surfaces. [1][6]

Note that cribbing collars will not prevent wood chewing. [6]

Keep in mind that physically restricting a horse’s ability to chew wood can result in an increase in their cortisol level, indicating increased stress. These deterrents do not address the underlying cause of the wood chewing behavior and may negatively impact the welfare of the horse by removing an effective coping mechanism. [2]

Preventing Wood Chewing

As noted above, once established, stereotypies are difficult habits to break. Therefore, avoiding the development of these behaviors is of utmost importance. [7]

Prevention of wood chewing and other stereotypies must start early in the horse’s life by providing your horse with a species-appropriate lifestyle. This means letting your horse be a horse and enabling natural equine behaviors such as foraging, movement, and socializing with other horses.

To prevent wood chewing and related oral stereotypies, follow these key management practices:

  • Feed your horse a forage-based diet with hay supplied at 2% of the horse’s bodyweight per day.
  • Provide free-choice hay and use slow feeders to ensure the horse doesn’t go long periods without hay.
  • Minimize feeding of grain-based concentrates and avoid large meals containing excess starch and sugar.
  • Allow for plenty of turnout time with other horses.
  • Implement a regular exercise routine for your horse, but avoid overtraining.
  • Wean young horses after six months of age.

Remain vigilant for any signs of wood chewing or other stereotypies in your horse. If you observe any abnormal behavior, prompt management changes should be implemented to address the underlying cause of the behavior.

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References

  1. Pearson, E.G. Reduced Horse Wood Chewing of Juniper. Oregon State University. 1999.
  2. Smulders, T.T. et al. Husbandry practices associated with the presentation of abnormal behaviours in Chilean Creole horses. Archivos de Medicina Veterinaria. 2012.
  3. Hothersall, B. and Nicol, C. Role of Diet and Feeding in Normal and Stereotypic Behaviors in Horses. Vet Clin Equine. 2009.
  4. Hothersall, B. and Casey, R. Undesired behaviour in horses: A review of their development, prevention, management and association with welfare. Equine Vet Education. 2012.
  5. Aley, J.P. et al. The efficacy of capsaicin as an equine repellent for chewing wood. Journal of Vet Behavior. 2015.
  6. Thal, D. Wood Chewing or Eating. Horse Side Vet Guide.
  7. Nagy, K. et al. Possible influence of neighbours on stereotypic behaviour in horses. Applied Animal Behavior Science. 2008.
  8. Elia, J.B. et al. Motivation for hay: Effects of a pelleted diet on behavior and physiology of horses. Physiology and Behavior. 2010.
  9. Krzak, W.E. et al. Wood Chewing by Stabled Horses Diurnal Pattern and Effects of Exercise. J Animal Sci. 1991.
  10. Henry, S. et al. Domestic Foal Weaning: Need for Re-Thinking Breeding Practices? Animals Basel. 2020.