Addressing Equine Obesity: Implications, Identification, and Management

October 3, 2023

How horse obesity can affect the horse's health

Weight gain and adipose deposition occurs when a horse’s nutritional intake exceeds his physical output. Growing affluence in developed countries has increased the time and money available to spend on leisure activities such as horse riding. Low to moderate physically-demanding lifestyles and the availability of affordable, energy-dense (high carbohydrate) foods as well as increased productivity of grass crops composed of plants intended for cattle and too rich for horses, has led to an increase in the incidence of obesity. When horses are obese and overweight they are less capable of performing as expected to “do their job” and coping with the physiological stresses of being ridden. As seen in other species including humans, obese horses may also be more likely to develop osteoarthritis.

What is the prevalence of horse obesity?

Until recent years the prevalence of horse obesity was mostly unknown but several studies have investigated the incidence of obesity in horses. The first study to look at the prevalence in the UK was published in 2008 and examined the incidence in pleasure horses in Scotland and most interestingly the association between body condition score and the owners perception of body condition score. The researchers found that 45% of 319 riding horses were considered “fat” or “very fat,” with 10% of those horses in the “very fat” category (Wyse et al 2008).

This is supported by a study in the U.S. which examined 300 horses and found that 51% of them were overweight and 19% (of the 300 horses) were considered obese (Thatcher et al 2007). A similar second study in the U.S. this time in North Carolina examined 366 horses and found that 48% of the horses scored a 6 or higher on the Henneke scale and 20% scored a 7 or higher (Owens et al 2008).

An analytical clinical study on the prevalence of and risk factors for equine obesity in Great Britain (Robin et al 2015) found that compared to competition horses, horses used for pleasure or not ridden were more likely to be obese.
Although there is little published data to support the concept of “easy keepers” or “good doers”, a study found Icelandic horses gained weight whereas Standardbred horses lost weight when they consumed the same diets and the same amount of digestible energy (Ragnarsson et al 2011).

Identifying an obese horse

There are two easy to use systems to assess Body Condition Score (BCS) in horses. The nine point system, developed by Dr Henneke and a simplified five point scoring system. The Henneke system assesses six areas of the body - neck, withers, shoulders, ribs, loins and tailhead. Each area is given a score from 1 to 9, with a BCS of 5 being considered ideal for pleasure horses, and a BCS over 7 indicating obesity.

Obese horse showing signs of excess weight

The five point system divides the horse into 3 sections – neck and shoulder, back and ribs and bottom. Each section is given a score between 0 and 5, where 0 = emaciated, 1 = poor, 2 = moderate, 3 = good, 4 = fat and 5 = obese.

Both systems are based on visually assessing the horse and feeling for fat deposits/bones as described by the system. A basic description and rule of thumb described by the laminitis site to follow is: If you can feel and see bones, the horse is too thin, if you can neither feel nor see bones, the horse is too fat, If you can feel but not see bones, the horse is just right.

One of the problems with these body condition or fat scoring systems is they are subjective and arguably not all horse owners can assess their own horse or pony accurately.

The same Scottish study cited above identified that many of the horse owners taking part were not able to correctly identify their horse’s body condition score. Misclassification by owners was most commonly due to them underestimating their horse’s body condition; the owners of fat horses were most likely to score their horse incorrectly, and only 50% of the owner estimates for fat horses agreed with the expert classification.

This finding indicates poor ability among horse owners to assess body condition accurately, and a tendency for owners of obese horses to underestimate their horse’s condition.

Health problems associated with horse obesity

Inflammation

Adipose (fat) tissue is now regarded as a highly active metabolic organ that secretes hormones that play a major role in energy balance for the body and satiety (feeling full). Furthermore, adipose tissue produces inflammatory proteins called cytokines. In fact, in humans, obesity is considered an inflammatory state due to the amount of inflammatory compounds produced by the adipose tissue. It is also believed that these cytokines play a role in causing oxidative stress, damaging tissues, and affecting metabolism.

Laminitis

Metabolic causes of laminitis are associated with obesity, but they are poorly understood. It is believed there is a complex interaction between cytokines and the vasculature (blood vessels within the hoof), resulting in inflamed laminae.

Insulin resistance

Normally the hormone insulin functions to move glucose from the bloodstream into tissues such as skeletal muscle and adipose tissue. Insulin does this by triggering the movement of specific insulin-sensitive glucose transporters (called GLUT4) from within the cell to the cell membrane. Once these transporters are at the cell membrane, glucose can move from the blood into the cell. Insulin resistance occurs when the hormone insulin does not effectively regulate blood glucose.

Research has shown feeds higher in starch and sugar (and resulting in higher glycemic indices) lead to reduced insulin sensitivity compared to hay alone or feeds higher in fat and fiber (with lower glycemic indices) (Hoffman et al., 2003, Pratt et al., 2006).

Ways to combat horse obesity

The treatment for obesity is calorie deficit through dietary management and appropriate exercise. It is important to maximize chewing time for the food obese horses consume to mimic their natural feeding behaviour. The use of a slow feeders such as the Haygain Forager can help with this. See how the Forager helps with obesity.

It’s important to feed plenty of forage, about 1.2 to 1.5% of the horse’s body weight daily in forage. Never feed less than 1%, as this can lead to problems including hindgut dysfunction, gastric ulcer formation, and stereotypic behaviour development. However, obtaining forage with a low nutritional value for obese horses to reduce the amount of calories they consume. Typically these hays are more "stemmy" and fibrous but getting the forage analysed is advised.

Sharon Smith MSc talks about how the Forager mimics natural grazing behaviour and the benefits including obesity management.

Ideally forage fed to obese horses should contains <100g WSC/kg DM which is the equivalent to <10% or be processed to reduce the sugar content.
If finding a high-fibre hay with a low WSC content is not possible then the latest published research suggests a combination of both soaking and steaming is the next best option. Moore-Colyer et al 2014 recommends a 9 hour soak followed by a 50 minute steam for reducing WSC.

One of the key benefits of steaming hay with a Haygain hay steamer is you will improve the hygienic quality even after a soak-induced increase in bacteria.