Obesity has been defined as a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and increased health problems. Now, let’s talk about equines specifically.

Horses are grazing animals but, unfortunately, the pastures we have today are not the same as what they evolved to eat. Forages in our pastures today are much higher in calorie content than the types of grasses that horses evolved eating. They grazed on moderate to poor quality forages, often covering several miles a day to find feed in sparsely vegetated areas.

Today’s management strategies have placed horses in unnatural confinement that restricts grazing activity within the limits of fences, while providing easy to find and high quality forages.

The ultimate confinement with limited access to pasture is represented by horses that are stable kept, with limited turnout. These horses do not have to travel at all to find feed, since it is provided in the stable and, thus, are not expending any calories looking for food.

The basic cause of obesity is the consumption of more calories than calories expended, usually from a combination of too much or the wrong type of feed, and often combined with a lack of exercise.

Traditionally, working horses needed more calories than they could get from forage alone and were fed grain to make up the deficit.

Today, most horses are no longer used for work; many are kept as pleasure and recreational horses. Their calorie expenditure is very low when compared with horses in the past.

What is a ‘good doer?

What makes one horse fat and one thin on the same feed and exercise regime? To answer this let’s go back to horses in their natural habitat.

During Autumn, horses ingest increasing quantities of available forage and gain fat in preparation for Winter when food tends to be lacking. Increased appetite and weight gain at this time, along with the acquisition of a thick hair coat, are stimulated in herbivores by the secretion of specific hormones from the hypothalamus and pituitary glands. These changes represent a critical survival mechanism, allowing the animal to use stored body fat throughout Winter.

In nature, the acquired fat stores should be depleted prior to the onset of Spring and the growth of new grass. However, current management practices in horses have removed this seasonal change in forage availability. Horses have constant access to nutrient-rich diets and the harshness of Winter is all but avoided with the use of conveniences, such as stabling and blankets.

Some horses, through natural selection, have inherited genetic traits that have facilitated their survival through periods of environmental harshness. These animals, including horses, are said to have inherited ‘thrifty genes’.

Most pony breeds are easy keepers and smaller, hardy horse breeds, such as the Arabian, have many representatives with this trait. Many draft horse breeds, such as the Percheron, also tend to display a more thrifty appearance, as do most mules and donkeys.

Detecting obesity

The prevalence of obesity in horses is often overlooked; many horse owners deem a degree of obesity as normal, acceptable and even desirable. In some equine disciplines, horses are judged competitively by their physical characteristics. In these events, a degree of fleshy appearance is often judged to be an advantage in the show ring.

Various methods have been recommended for the purpose of assessing the body fat of equines, including the body condition score (BCS) and the use of ultrasonography to assess subcutaneous fat thickness near the tail head. Ultrasonography is not a practical tool for horse owners, so we recommend they become very familiar with the body condition scoring system!

By doing this, you will be able to proactively manage your horses so they are always in an ideal, healthy body condition. The body condition scoring system (http://www.hygain.com.au) uses a 1 to 9 scale – where 1 is emaciated and 9 is extremely obese.

It is a subjective system, so it is important horse owners look at documented pictures of specific condition scores and carefully evaluate based on the description given for each numeric score. Using this system, a BCS of 5 or 6 in considered ideal for most equines.

Human studies show regional fat deposition, such as abdominal fat, is more predictive of metabolic disease than overall body fat. The BCS system determines overall fatness of horses, but does not differentiate between specific regions of fat.

Like abdominal fat in humans, neck crest fat in horses has been suggested to be associated with insulin resistance and increased risk for laminitis. Recent research has developed a novel scoring system for grading neck crest fatness.

The ‘cresty neck scoring system’ (CNS) is on a scale of 0 to 5 – where a score of 0 equals no visual appearance of a crest, and a score of 5 equals enormous and permanently drooping to one side. When dealing with horses with a CNS of 4 or 5, we must be cautious of feeding diets high in sugar and starch.

Consequences of obesity

The effects of obesity include exercise intolerance, reduced performance, poor body temperature control, decreased reproductive performance and the development of benign fatty tumours within the abdomen that can cause colic.

Obesity contributes to the onset and increase of insulin intolerance in horses. Some equine conditions that have been associated with insulin resistance may, therefore, be more likely in obese horses, such as laminitis, cushing’s disease, osteochondrosis and hyperlipemia.

Management strategies

With equine obesity becoming an increasingly common problem, it has led many owners to seek safe weightloss solutions for their horses. In most cases, we advise restricting diet and increasing exercise but, with some horses, for instance those suffering from laminitis, exercise might not be an option. This often leaves dietary restriction as the only means for weightloss, making it increasingly more difficult.

As we have discussed, the horse is a grazing animal and, as a result, it is extremely important to ensure adequate forage is incorporated into any weightloss program. Without adequate forage, the horse will suffer from various other health issues, such as gastrointestinal disorders, colic and gastric ulcers, to name a few.

The normal intake of forage for a healthy horse is 2 to 2.5% of bodyweight (BW); this equates to 10 to 12.5kg for a 500kg horse. When implementing a weightloss program, we recommend limiting forage intake to between 1 and 1.5% of BW (5 to 7.5kg for a 500kg horse).

If horses are stabled or on a dry lot, this forage must be supplied frequently throughout the day to ensure gastric ulcers do not develop. Other practices, such as slow feeders and slow feed hay nets, can be used to slow down the horses’ consumption rate. Horses that have access to pasture should have limited turnout time and may also need to wear grazing muzzles.

Forage alone, however, is deficient in several critical nutrients and, therefore, must be supplemented to meet the horse‘s nutrient requirements. A low intake vitamin and mineral pellet – more commonly referred to as a ‘ration balancer pellet’, is an ideal product in a weightloss program.

It is important to note, like people, each horse’s metabolism is different and, therefore, responds differently to feed restriction. Weightloss is a slow process and, where possible, feed restriction should be coupled with exercise.