Most of us have looked at our horses at some point and wondered if they are a healthy weight. When we see them every day, it can be hard to assess them objectively and small changes may be missed. Nonetheless, maintaining a healthy weight is a key part of longevity and soundness, so it’s important to understand how to assess body weight in horses and some common consequences of obesity.
Obesity assessments
Weighing a horse on a scale is not feasible for many horse owners. Although it is helpful when determining medication dosage, body weight alone can be uninformative. To better assess each horse, we do a hands-on exam to determine their body condition score (BCS).
BCS is a scale that appraises fat in the neck, shoulders, withers, over the ribs, spine, and tailhead. Horses are scored on a 1-9 scale, with 1 indicating extreme emaciation and 9 indicating extreme obesity. A score of 5 is considered ideal for most horses. Horses with a score of 5 have a flat lumbar region, ribs that can easily be felt with a flat hand but cannot be seen, rounded withers, a somewhat spongy tailhead, and a neck that blends smoothly with the shoulders. Race-fit Thoroughbreds are often a 4, with slightly visible ribs and less fat coverage over their muscles. Horses headed into a cold winter and mares being bred should be a 5-6, accounting for extra energy storage to stay warm and for reproduction, respectively.Age and conformation also matter. Just like us, fat can sag with time. As such, it is important
to look at the horse holistically, considering muscling, conformation, age, and fat scores across all regions. Even so, BCS is subjective and thus it may be helpful to get a second pair of hands to assess the horse.
Another useful tool is the cresty neck score (CNS). This tool simply assesses the amount of fat in the crest of the neck above the nuchal ligament. It is a six-point scale from 0-5. A score of 2 is often considered ideal, indicating a horse with a noticeable appearance of a crest, with fat distributed evenly from poll to withers, and can be cupped with one hand and moved side to side. Again, other factors should be considered, such as muscling and testosterone, which can impact the appearance of a crest. For example, a baroque stallion competing in upper-level dressage would be expected to have a much larger crest than a race-fit Thoroughbred mare, even though they are both healthy weights.
Equine metabolic syndrome
Increased body condition score (≥7) and cresty neck score (≥3) are each associated with increased risk of insulin dysregulation, a hallmark of equine metabolic syndrome (EMS). EMS is a collection of metabolic risk factors that predispose a horse to endocrinopathic laminitis (laminitis driven by hormonal imbalances). Horses with EMS typically have a combination of insulin resistance, hyperinsulinemia, hyperglycemia, and hypertriglycidemia. Some horses with EMS also experience increased blood pressure, heart rate, and heart size.
The most serious concern with EMS is the risk of laminitis. Laminitis occurs when the laminae, an interlocking structure that connects the hoof capsule to the coffin bone and underlying soft tissues, begins to separate and fail. This debilitating process can cause the coffin bone to rotate downwards. This separation and rotation are painful and often irreversible.
Horses experiencing laminitis will adopt a “sawhorse” stance, with the front legs stretched forward, away from the body, and the back legs stretched forward and under the body. This stance relieves the pressure from the toe of the hoof. Severe and repeated bouts of laminitis will cause the coffin bone to rotate downwards towards the sole of the hoof, causing permanent damage. This change may warrant euthanasia due to pain.
Although obesity increases the risk of EMS and thus laminitis, both can occur in normal weight horses. There are also several known breed predispositions, including pony breeds, Quarter Horses, Warmbloods, and Tennessee Walking Horses. Upwards of 20% of U.S. horses may have hyperinsulinemia, suggesting this is a common condition. The risk of EMS increases with lack of exercise, a key insulin regulator. Insulin levels have also been found to increase with age in horses, suggesting that older horses may also be more vulnerable to laminitis.
Diagnostic tools
To diagnose EMS, baseline blood insulin concentration is important. Blood insulin level after a fasted oral sugar challenge is a more sensitive tool for identifying EMS. Assessing blood glucose alone is not typically informative for EMS but can be used to rule out diabetes mellitus. Lastly, leptin, a hormone produced by fat cells, is increased in obese horses. Testing serum leptin levels can be used to identify horses at risk of EMS and can also be helpful in monitoring weight loss.
Ultimately, weight management is a crucial component of responsible horse health maintenance. Owners should work with their veterinarian to assess their horse’s body condition and to learn how to monitor it. At the Equine Reproduction Laboratory, we develop feeding plans to maintain healthy weights of all horses in our care, especially because laminitis prevention is crucial for all breeding horses.