By Dr. Tania Cubitt & Dr. Stephen Duren, Ph.D.

Weight loss is simply a result of more calories being used by the body than are being consumed. There are several potential causes of chronic weight loss in horses. These causes include poor quality or limited feed supply, health and disease problems, as well as social interaction and competition among horses. Chronic weight loss can also be the result of starvation. Starvation can be caused by intentional neglect, ignorance, economic hardship of owner, disease, dentition, pecking order, parasites, or seasonal variation in availability of pasture. Remarkably, horses can survive chronic weight loss.

It has been reported that horses can lose 30 percent or more of their body weight and still survive. Horses in this condition will have very little muscle mass and will be very weak. They will need special attention and a sound nutrition program to return to a proper body condition. Even with the best of care some horses won’t survive, especially horses that have lost 50 percent or more of their body weight.

Causes of Weight Loss

Poor Quality or Limited Feed

Perhaps the most common cause of weight loss is poor quality or limited feed. Forage (hay and pasture) plays a significant role in chronic weight loss since it is the primary component of the diet. In addition, it is difficult to accurately determine the quality of hay and pasture. In other words, a person may be providing enough forage for their horse but the forage is of such poor quality the horse is not able to properly digest it.

If horses have free choice access to as much forage as they will consume and they are losing weight, better quality forage must be provided. In addition, a grain concentrate can be added to provide extra nutrients that are missing in poor quality forage. 

The other common mistake made with feeding horses is simply to not provide enough feed. For example, an adult horse requires at least two percent of its body weight per day, or 9 kg for a 450 kg horse (20 lb for a 1000 lb horse) in dry hay. If the horse is being fed less than this amount, often the result will be chronic weight loss.

Photo: Poor quality feed is a common cause of weight loss. If horses are losing weight despite having free access to as much forage as they will consume, better quality forage and a grain concentrate to replace missing nutrients should be provided. Photo: ©Canstockphoto.com/ponytail1414

Health & Disease Issues

Health and disease issues cover an array of topics ranging from dental problems to parasite infestation to diseases such as lameness, chronic obstructive pulmonary disease (COPD) or heaves, Cushings, gastric ulcers, equine infectious anemia (EIA), chronic diarrhea, cancer, Lawsonia, liver or kidney disease, chronic infections, and neurologic conditions.

Dental problems are a significant cause of weight loss in horses. If horses cannot properly chew their feed, they will not be able to utilize the nutrients in feed. Signs that a horse may have dental problems include: dropping feed while chewing, nasal discharge, foul-smelling breath, and facial swellings. It is important to do a complete oral exam and not just look at the teeth, as other disease processes may be present in the horse’s mouth.

Photo: A thorough dental exam can identify problems and diseases that might be preventing the horse from chewing its feed properly, resulting in nutrient deficiencies and weight loss. Photo Credit: ©Canstockphoto.com/Kiep

Internal parasites such as worms compete with the horse’s body for nutrients and often result in weight loss. Parasites may become resistant to many of the common dewormers, so it is important for your vet to check the feces for parasite eggs to rule out this problem. Even then, larval parasites can be involved that cannot be found in a routine fecal analysis, and treatment for larval parasites may be required to halt chronic weight loss. 

A number of other diseases and chronic health problems can result in weight loss. Any disease that affects a horse will increase both protein and energy requirements, often resulting in weight loss. In order for horses to recover from the disease and gain weight, the disease or health issue must first be treated and resolved.

Social Interaction

As most horse owners have witnessed, horses can be very aggressive toward each other. If you are group feeding horses,

you have the added complication of the natural hierarchy of dominance. Not only can younger, smaller, more timid horses be pushed away from the feeders, but they may be experiencing high levels of stress which not only includes expending more energy, but can predispose to health problems including stomach ulcers and colic. In general, it is important that underweight horses be fed separately. This will ensure they are actually getting the amount of feed which is intended for them. 

Monitoring Weight loss

Before any nutritional intervention is imposed, a proper estimate of the horse’s body weight and body condition score is needed. Estimating body weight and body condition on a routine (monthly) basis should be a key component of any horse management program. Tracking the weight of a horse will allow the owner to properly calculate the amount of feed required by the horse in order to gain, lose, or maintain body weight, as well as indicate how much weight the horse has lost or gained over a certain period of time.

Body weight can be measured by three simple techniques. A large livestock scale is the most accurate method of weight estimation, but a weight tape is also quite useful. If you do not have a weight tape you can also use a simple cloth measuring tape. Measure the heart girth, then measure the length of the horse from the point of the shoulder to the point of the buttock. Use the following equation to estimate body weight (Carroll & Huntington, 1988):

Weight (kg) = [heart girth (cm) x heart girth (cm) x body length (cm)] / 11,990

Or:

Weight (lb) = [heart girth (in) x heart girth (in) x length (in)] divided by 330 

Body Condition Scoring (BCS) is also a useful tool when estimating actual body fatness. Body condition scoring involves the palpation and visual assessment of the degree of fatness of various areas of the horse, such as: over the ribs, tail head area, neck and withers, and behind the shoulders (Henneke et al., 1983). The scoring system uses a numeric scale of 1 to 9 where 1 is emaciated and 9 is obese. Regular condition scoring of your horse will help in detecting weight loss patterns before they become chronic.

Weight Gain Strategies

Once you have rectified the cause of the chronic weight loss in the horse it is time to begin implementing feeding strategies to enhance weight gain. The 2007 National Requirements for Horses suggested that it takes 16 to 20 kg (35 to 45 lb) of gain to change a horse’s body condition score by one unit (based on a 500 kg or 1100 lb horse). We can safely achieve this amount of weight gain in approximately 60 days by adding additional calories to the diet. Care should also be taken when feeding for weight gain not to cause digestive disturbances with the increased feed intake. The question then becomes: What should I feed my horse for weight gain?

There are many feed ingredients that we can add to the diet to increase a horse’s body weight including oats, rice bran, beet pulp, alfalfa, and oil. It is important to understand the caloric content of each of these ingredients in order to evaluate how much will need to be fed to achieve the desired weight gain. Table 1 outlines how much of each of the chosen calorie sources would need to be fed over a 60 day period to achieve 18 kg (40 lb) of weight gain in an average sized 500 kg (1100 lb) horse. This is in addition to the horse’s maintenance diet, e.g., if the horse was currently being maintained on 7 kg (15 lb) of hay and 1.8 kg (4 lb) of sweet feed and you chose to use beet pulp as your additional calorie source you would need to feed an additional 2.1 kg (4.6 lb) of beet pulp (before soaking weight) for 60 days to gain around 18 kg (40 lb).

Typically we recommend first increasing the amount and quality of forage available to the horse. Adding alfalfa hay, chaff, or pellets will increase the calories content of the diet as well as supplying other critical nutrients such as amino acids and minerals. Next we can start to gradually increase the grain portion of the diet – this must be done with care so as not to cause any digestive disturbance. Then we should top dress the grain with a fat supplement or gradually switch the horse over to a high fat concentrate.

Fats and oils are commonly used in horse feeds to increase the calorie content of the feed or to replace the calories supplied by carbohydrates. Fat supplementation has many benefits, which include providing calories for weight gain and providing essential fatty acids to improve skin and coat condition. On an equal weight basis vegetable oil provides horses with 2.5 times the digestible energy of corn and nearly three times the digestible energy of feeding oats. Thus, adding fat to the diet increases the energy density (number of calories per kilogram of feed) of the diet. Thin horses will gain weight and do so without having to eat as much grain if the diet is fortified with additional fat.

Weight loss in horses can be caused by many different factors; once you have resolved those issues and started your horse on a more calorie dense diet it will begin to gain weight. Remember, weight gain is a slow process – do not expect results overnight. 

Reprinted with permission from Otter Co-Op.

Main article photo: Horses can lose 30 percent or more of their body weight and survive, but will have very little muscle mass and will be weak. Horses in this condition need special care and sound nutrition to restore them to proper health and body condition. Photo: ©iStockphoto.com/rollover

This article originally appeared in the October 2014 issue of Canadian Horse Journal.