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/or 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 situations that restrict grazing activity within the limits of pasture fences while providing easy to find, 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 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? To answer this let’s go back to horses in their natural habitat. During the autumn season, horses ingest increasing quantities of available forage and gain fat in preparation for the winter season 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 that allows the animal to use stored body fat throughout the winter months.
In nature, the winter season is set and the acquired fat stores should be depleted prior to the onset of spring and the growth of new grass. 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 are said to have inherited “thrifty genes.” The extent to which different breeds of horses have inherited thrifty genes is unknown, but tend to be found most often in breeds originally developed to survive under harsh conditions. 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. We commonly refer to these equids with a variety of terms such as “good doer “or “easy keeper”.
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 and frequently condition score their animals. By doing this they will be able to proactively manage their animals so that they are always in an ideal, healthy body condition. The body condition scoring system uses a 1 to 9 scale where 1 is emaciated and 9 is extremely obese. It is a subjective system so it is important that horse owners look at documented pictures of specific condition scores and carefully evaluate based on the description given for each numeric score Table 1. Using this system, a BCS of 5 or 6 in considered ideal for most equines.
Human studies show that 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 zero equals no visual appearance of a crest and a score of five 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 as these may make worse any underlying risk for metabolic disease.
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, hyperlipemia and inflammation.
With equine obesity becoming an increasingly common problem it has led many owners to seek safe weight loss 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 weight loss, 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 weight loss 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 body weight (BW), this equates to 10 to 12.5kg for a 500kg horse. When implementing a weight loss 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 wear a grazing muzzle.
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”, such as HYGAIN® BALANCED® is an ideal product in a weight loss program. HYGAIN® BALANCED® offers little calories while being highly fortified in critical vitamins and minerals and can be fed at a rate of 0.1% of BW (500g for a 500kg horse).
It is important to note that like people, horses’ metabolisms are all different and therefore respond differently to feed restriction. Weight loss is a slow process and where possible feed restriction should be coupled with increased exercise.