Pesky Pudgy Ponies: Equine Obesity and the Behavior Consultant

Written by Justice Everett Smith, MEd

Summary: Obesity poses a significant threat to equine welfare, affecting approximately 40% of horses in the U.S. and U.K. Fortunately, it is one of the most preventable health issues in the horse.1 While obesity has historically been viewed as a strictly physical condition, evidence shows that obesity is linked to behavior in the horse. The behavior consultant can play a major role in helping overweight horses by working closely with owners to prevent, identify, manage, and resolve obesity.


Equine obesity: An overview

Obesity is defined as the excess accumulation of adipose tissue (fat) to the point that there are associated negative health consequences for the animal. In domestic horses and donkeys, obesity is one of the most common and preventable welfare issues that we face today. Addressing equine obesity is the responsibility of every member of the horse industry, but behavior consultants can play a key role in the humane prevention and resolution of equine obesity through their unique partnerships with owners, trainers, and veterinarians.

The prevalence of overweight and obese equines varies greatly among populations. Numbers as low as 1.4%2 and as high as 40%3 have been reported in the United States, while estimates of populations in the United Kingdom range from 31.2%4 to 90.8% in shown Mountain and Moorland ponies.5 Studies that rely on owner-reported data show lower incidences of overweight and obese horses,4 suggesting that owners are less qualified to assess their own horses. The literature consistently shows that miniatures, ponies, cobs, and drafts are significantly more at risk of suffering from obesity.4,6,7 Additionally, horses kept primarily for leisure and non-ridden horses have been found to be at a higher risk of being overweight or obese.4 Any horse — regardless of breed type — can become overweight, but it is especially important that horse industry professionals monitor the body condition of our most vulnerable animals.

It is well documented that obesity can contribute to a plethora of negative effects on the physical health of a horse, including laminitis, orthopedic disease, insulin dysregulation, reduced fertility, hyperlipidemia, increased stress on the cardiovascular system, colic, diabetes, and hyperthermia.8,9,10 Often ignored, however, are the behavioral impacts associated with obesity. Poor performance,11 lethargy, exercise intolerance, and excessive fatigue9 are common behavioral presentations of obesity. Behavior consultants should be aware of these issues and take them into account when working with an overweight equine. Research also suggests that ridden misbehavior events (such as bucking, rearing, and bolting) are more common in horses that are obese.12 This is a critical finding — it means that obesity in the horse is not only an equine welfare issue but also an issue of human safety! It must be noted that this is not necessarily a causative relationship, and many factors, including lack of exercise and increased carbohydrate intake, likely contribute to this association.

Causes of equine obesity

Horses have evolved to spend about 16 hours a day eating high-fiber grass forage.6 A modern stalled horse, on the other hand, might spend about two to three hours eating in a day. High-energy rations, frequently high in sugars and starch, are often provided to stalled horses in (sometimes extreme) excess of their daily energy requirements. Even pastured horses and horses on forage-based diets are not immune to the modernization of animal feeding. Grasses used for feeding horses (including pasture and hay) have been artificially selected to be energy-dense and high in nonstructural carbohydrates (NSCs), like sugars and starches.10 The metabolism of the horse has evolved to accommodate large quantities of high-fiber forage, not feeds high in carbohydrates or fats.

In addition to being grossly overfed, the modern horse does not tend to get a lot of exercise. A leisure horse might only exercise two to four hours per week. Even horses at the highest levels of sport often only exercise for one or two hours a day. Owners have a tendency to overestimate the exercise that their horses get as well as the impact that exercise has on their horses’ energy expenditure.4 Research suggests that moderate exercise (40 minutes for four days a week) does not significantly impact the body condition of overweight and obese equines in the absence of dietary changes.13 Other factors, such as blanketing — which prevents normal thermoregulation and limits energy expenditure8 — are implicated in the prevalence of obesity in managed domestic horses.

There is a genetic predisposition to developing obesity in some horses.14 Horses managed and fed the same way can show inexplicable differences in body condition.15 Environmental factors, such as stress and sleep, have been shown to affect obesity susceptibility in humans. It is hypothesized that endocrine-disrupting chemicals in the environment, called obesogens, are also implicated in the obesity epidemic in humans.16 Research has not been conducted regarding these environmental factors on the incidence of overconditioning in horses. However the concurrent human, pet, and equine obesity epidemics may suggest a common factor in the environment. Further research into the role of genetics and obesogens on equine obesity is necessary.

Identifying obesity

Equine obesity is typically measured using body condition scoring (BCS). This is a method of evaluating body condition by assessing fat accumulation visually and by palpation in six areas: behind the shoulder, over the ribs, above the tailhead, and at the rump, withers, and crest of the neck. The size or shape of the belly is not a good indicator of body condition and should not be considered when assessing the fleshiness of a horse. A nine-point scale is used to evaluate equine BCS, with 1 representing an extremely emaciated animal and 9 representing an extremely overweight animal.17 The ideal range for most horses is a score of 4 to 6; horses with a BCS of 7 or more are considered to be obese. Body condition changes seasonally in free-ranging and pastured horses. Horses typically have a higher BCS at the end of summer (when forage is plentiful) and lose weight throughout the winter (when energy expenditure is high and forage is sparser).6

Most equestrians are familiar with body condition scoring, as it is often used as a management and assessment tool. Research shows, however, that owners and professionals in the horse industry are increasingly failing to recognize obesity.4,18 In my experience, horse owners are generally more likely to recognize a thin horse than a fat horse, and consider thinness to be a more significant welfare issue. Accordingly, it is increasingly the role of the behavior professional to be adept at recognizing and addressing equine obesity. It is recommended that everybody who works with horses is versed in body condition scoring. Taking this quiz every so often to test your accuracy can be helpful. Looking at fat horses all day really can start to shape what we perceive as normal!

Addressing equine obesity

Reduction of body weight can be achieved through dietary intervention. Restricted energy intake is the primary method for achieving an optimal BCS.19 Restriction of NSCs is commonly used to address insulin-resistant and laminitic horses.20 This is relatively simple to achieve with a stalled horse, but the energy intake of a pastured horse can be more difficult to manage (restricting grazing with muzzles will be discussed later). It is not within the behavior consultant’s scope of practice to recommend dietary changes, but owners with overweight horses are likely to ask for advice. These clients should be referred to an equine veterinarian or qualified equine nutritionist.

The most important part of successfully implementing dietary changes is owner/caretaker compliance. One study of weight reduction in client-owned horses found that about 30% of owners were compliant in restricting their horse’s intake, about 43% of owners were inconsistently compliant with restriction, and about 26% did not follow the protocols.19Owners might perceive weight management strategies as “cruel” and many feel emotionally satisfied by feeding treats or meals. Encouraging other welfare-enhancing interventions, such as increased social contact or enrichment, can help owners to feel better about executing dietary changes.21 The behavior consultant can be a great asset in helping owners comply with weight management interventions because they often have more contact with clients than veterinarians or nutritionists and are able to assist more in monitoring and motivating.

Equine obesity and behavior: What to know and how behavior consultants can help

Restricting grazing by muzzling

Limiting caloric intake by restricting grazing is a common method of preventing and addressing obesity in the horse. The primary means of restricting grazing are stabling, strip grazing, dry lots (paddocks without any grass, also called crew yards), semi-dry lots (paddocks with very limited grass, also called starvation paddocks), track systems (which can be with or without grass), and grazing muzzles.22 In some cases, intrusive methods such as stabling must be employed in the short term for the health of the horse. In most cases, however, less intrusive options can be effective. Track systems, in particular, can promote the health and welfare of horses by encouraging movement while reducing forage intake. However, setting up a track system can be expensive and labor intensive, and it can require a lot of space. Realistically, most horse owners are not able to implement serious management changes, such as creating a dry lot or a track system. It is the author’s opinion that grazing muzzles are the most practical and welfare-friendly grazing intervention for the average horse owner and should be a tool with which the behavior consultant is well-acquainted.

Using a grazing muzzle to restrict energy intake can prevent the progression of obesity; however, this intervention must be implemented properly in order to promote the welfare of the horse. The behavior consultant can play a vital role in making this happen by encouraging the appropriate use of the grazing muzzle from a behavioral perspective. Introducing the muzzle should be done with care. Teaching a horse to self-muzzle through positive reinforcement is convenient and much easier than chasing after a horse that has been “taught” to be muzzled through flooding. It is essential that muzzles fit properly and do not cause rubs. Horses might become more reluctant to cooperate with the application of a grazing muzzle over time, so consistent reinforcement is advisable. Recent studies did not find reduced acceptance of a grazing muzzle over time in horses that had been acclimated to it for at least six months.23,24

When miniature horses were fitted with grazing muzzles for 10 hours or 24 hours a day, no signs of increased physiological stress (salivary cortisol, heart rate, or heart rate variability) were identified when compared to unmuzzled horses.23,24 In miniature horses housed in a herd, wearing a muzzle for 24 hours a day was associated with a lower heart rate,24 possibly suggesting a cardiovascular health benefit to muzzling. Conflicting information is available on the efficacy of muzzling for 10 hours a day,23,24,25 although muzzling for 24 hours a day appears to result in weight loss consistently. Horses that are muzzled for 10 hours a day might eat more when unmuzzled to compensate for the restriction, while horses that are muzzled for 24 hours a day likely engage in a grazing pattern that reflects the slower rate of intake seen in free-roaming equids. Davis et al. (2020b) suggest that muzzling might impact social behavior, including social rank and aggression, although these effects were not statistically significant.24 Reduced autogrooming was found in muzzled horses housed individually and in a herd setting.23,24

The research shows that muzzling for 24 hours a day can effectively reduce body weight without significantly impacting the welfare of the horse. We can mitigate the welfare impact of reduced autogrooming by providing other opportunities for horses to engage in grooming behavior, like introducing automatic brushes, which have been shown to supplement and increase allogrooming.26 Despite this, the opinions of horse owners in regard to the use of grazing muzzles are polarized. A study of U.K. horse caretakers found that muzzling was considered to be second only to stabling as the worst restricted grazing method for welfare. Despite this, 38.6% who had used grazing muzzles said that they would use them again.21 A study in the U.S. found that 50.5% of overconditioned ponies in Maryland wore grazing muzzles, and it was the most used management tool for overweight equines. Despite this, owners were less satisfied with grazing muzzles compared to other weight reduction methods (exercise, dry lot, and hay nets).3 Using a grazing muzzle might be a hard sell for some owners and barn managers. Emphasizing the minimal behavioral restriction (socializing, grazing, exercise) imposed by grazing muzzles and the lack of increased physiological stress in muzzled horses might help to convince some owners.

The estrous cycle and obesity

Obese mares are more likely to show continuous reproductive activity throughout the year than non-obese mares, with many obese mares not entering seasonal anestrous normally.27 Most who work with horses are familiar with the “moody mare” trope. Undesirable behaviors and poor athletic performance have been reported to be related to the estrous cycle, particularly during the estrus phase (when the mare is “in heat”). Many owners seek veterinary intervention to manage their mare’s estrous cycle in an effort to decrease the occurrence of unwanted behavior.28 Because obesity is associated with a greater number of cycles throughout the year, it is likely that these interventions are sought more for obese mares. It is possible that weight reduction in the high-BCS mare could encourage normal seasonal anestrous, therefore reducing incidences of estrus-related undesirable behavior.

Dominance and obesity

Studies have shown that body condition score (BCS) in horses is positively correlated with dominance rank. Horses that are overweight or obese are more likely to be dominant individuals when housed in groups, independent of height and age. It is unknown whether this relationship is due to increased energy intake in dominant horses, an increased proclivity to dominance in larger horses, or the effect of another factor that increases both susceptibility to obesity and dominance.29One study found that obese horses spent more time interacting with herdmates than horses with a moderate BCS, likely a reflection of their typically higher dominance rank.15 Based on this research, it is advisable to consider BCS when introducing horses and when keeping horses in a group. It is possible that changes in body condition resulting from weight loss or weight gain could disrupt established herd dynamics. It is important to note that social rank has not been found to be related to learning performance in horses.30 It is the author’s opinion that it is typically unnecessary to consider dominance rank when working with or training horses.

Using appropriate reinforcers

Some owners and trainers employ the use of reinforcers that are high in calories and NSCs, like sugary treats. This can contribute to the development of obesity and prevent or slow weight loss. Finding a reinforcer that is both effective and does not contribute to obesity can be a challenge. One study comparing grain to hay as reinforcers for horses found no difference in the time to achieving the initial learning. However, when the reinforcers were switched, horses that had originally been reinforced with grain performed the behavior significantly less for hay and the horses that had originally been reinforced with hay performed the behavior significantly more for grain.31 Another study found that the diet given outside of the experiment influenced the efficacy of different reinforcers. Horses that were fed a pelleted feed performed more behaviors to attain hay, and horses that were fed hay performed more behaviors to attain pellets.32 A recent study by Platzer and Feuerbacher (2022), comparing the reinforcement efficacy of different grains with varying NSC content and texture, found little difference between them, suggesting that low-NSC grains can be used for obese horses on modified diets with little effect on their learning.33

The literature around the reinforcement value of different feeds can help to inform behavior modification work with overweight equines by giving us a few guidelines to follow when choosing a reward:

  • The initial reinforcer matters. If horses are accustomed to working for a highly palatable reward, they will likely show a reduction in responses when switched to something less palatable.
  • The outside diet of the animal matters. Horses that eat a lot of grain are more likely to respond to hay and vice versa. This is important to note when working with equines on a modified diet.
  • Grains appear to be equally reinforcing, regardless of NSC content. We can modify the reinforcer used to accommodate special dietary needs without necessarily sacrificing learning efficiency.
  • Finally, while it might seem appealing to forgo food rewards entirely when working with an overweight or obese horse, it must be noted that tactile contact (such as wither scratching) is not an efficient reinforcer when compared to food rewards.34 One study found that neck patting had no reinforcement effect for horses.35

Discussions with owners and caretakers

Owners are often unaware of their horses’ overweight body condition. The behavior consultant might be the first person to suggest that a horse is obese. This can be a very sensitive topic for many owners and must be handled tactfully. Studies in canine obesity have found that overweight owners are significantly more likely to have overweight dogs36 and it is possible that a similar trend exists in equine owners (although to the author’s knowledge no such research has been conducted to date). Discussing this topic with an overweight owner might be particularly sensitive. Owners with a history of disordered eating might also find the topic to be triggering. Equestrian athletes have higher rates of eating disorder symptoms than the general public — one study found that 42% of collegiate riders reported disordered eating behaviors.37 It is essential that the behavior consultant is intentional and delicate when discussing this topic with any owner.

On the other hand, many owners are well aware of their horse’s overweight body condition and are keen to discuss it in a light-hearted, joking manner. The horse industry as a whole has tended to ignore the welfare consequences of overconditioning, although this knowledge gap has been improving in recent years, many owners are unaware of the significant impact obesity can have on their horses’ health. While it is necessary to be delicate, it is important that the behavior consultant does not downplay this issue. From the author’s experience, stressing the relationship between obesity and laminitis can be impactful for any owner. Because humans are not affected by laminitis, it is less likely to elicit personal feelings around weight and perceived health. Most owners will, however, recognize the serious nature of laminitis and are highly motivated to avoid it. Equine obesity is not an aesthetic issue and should never be discussed or treated as such.

Within some discipline and breed communities, overconditioned horses are the norm. A study of Mountain and Moorland show ponies found that over 90% were classified as overweight or obese. A study of hunter judges in the United States and Canada found that judges underestimated the body condition of overweight and obese horses and were significantly more likely to penalize a thin horse than a fat horse.38 It is important to note that owners are unlikely to recognize the significance of their horses’ condition when it has been normalized within their equestrian community. When working with owners, it is important to account for how their past experiences have influenced their current perceptions of obesity. This can be particularly prevalent when working with owners or managers of rescue horses, who, in the author’s experience, tend to have an extreme aversion to perceived thinness due to experiences with underweight horses.

Many owners perceive weight reduction practices to have negative welfare impacts for their horses. Owners who are aware of obesity as a threat to their horses’ health often view it as something to be combatted, referring to weight management as a “battle” or “war.” It is important to communicate the positive impacts of weight management on equine welfare, behavior, and health. In addition to these benefits, conveying that managing overweight and obese equines can be more expensive may help to motivate owners. A study of a population of horses and ponies in Maryland found that overconditioned equines cost, on average, an additional $434.18 to manage annually.3 Owners, trainers, and managers are likely to be more enthusiastic about implementing weight management strategies when they are aware of the financial impacts of equine obesity.

Final thoughts

Most equestrians are well aware that overweight and obese horses are more likely to suffer from a myriad of physical health problems, including acutely painful laminitis. Many owners, however, are unaware of the behavioral impacts of obesity. The behavior consultant should be cognizant of equine obesity and adept at accurate body condition scoring in order to address this common problem with clients. The ability to tactfully convey the ramifications of obesity, as well as various weight management strategies, on horse welfare is an essential skill for today’s behavior consultant.

References

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Justice Everett Smith is passionate about improving the lives of horses, donkeys, and mules through research and education. His research interests include equine obesity, human-horse relationships, and equid hybrids. He recently finished his master’s degree in equestrian education. You can contact him at justicee@ucla.edu.

TO CITE: Smith, J.E. (2024). Pesky pudgy ponies: Equine obesity and the behavior consultant. The IAABC Foundation Journal 29, doi: 10.55736/iaabcfj29.3

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