Weight Loss in Horses

Thin body condition of a horse might represent true "weight loss," or, more likely, it might be secondary to inadequate calorie intake over a period of time. The identification of a thin horse is usually not difficult--the horse's owner, stable manager, and veterinarian can clearly see that a horse is underweight. For a time, weight loss or poor condition might be hidden by a long winter coat, or under a winter blanket. Determining a horse's body condition score can be useful in adding a more objective measurement to a subjective finding such as weight loss. Additionally, determination of a horse's ideal weight depends on the breed of horse and intended use. For example, an event horse is usually in leaner body condition than a show hunter.

There are three main causes of unplanned weight loss: Malnutrition, parasitism, and dental problems.

Malnutrition means the horse isn't receiving enough calories. This might include inadequate amounts of hay and grain, poor-quality feed, or that there's competition for feed in a turnout situation. Competition arises when, for example, a bossy Quarter Horse is housed with a high-strung Thoroughbred. Each horse might be fed appropriate amounts of hay and grain for his body weight, but the Quarter Horse might be eating his intended (smaller) meal and chasing the Thoroughbred away from his much-needed meal.

Parasitism might rob the horse of calories through the parasites' consumption of nutrients or by inflammation associated with parasite burden. Regular (every two to three months) administration of deworming agents in association with routine fecal egg counts should minimize the impact of parasites on the horse's weight.

Dental problems can limit the horse's chewing efficiency, making digestion incomplete. The presence of broken, loose, or infected teeth can make chewing so painful that the horse stops eating.

There are many other causes of weight loss in horses, including kidney and liver disease, endocrine problems, inability of the intestines to absorb nutrients (malabsorption), chronic infection, gastric ulcers, presence of intestinal sand, and internal tumors. In general, addressing the "Big 3" causes of weight loss is a good place to start. After performing a complete physical examination, your veterinarian might elect to draw blood for a complete blood count and chemistry panel. An evaluation of the hay and grain as well as management and stabling methods might reveal problems contributing to the horse's weight loss. The veterinarian can evaluate the horse for sharp enamel points, loose or broken teeth, foul mouth odor (a sign of a possible rotten tooth), and infected gingiva or teeth. This exam is best made through use of a full-mouth speculum, which allows each tooth to be carefully palpated and visualized. The veterinarian can review deworming methods and collect a fecal sample so an egg count can be performed.

It is very helpful to record a baseline weight with a weight tape and to monitor progress weekly. It is advisable to have your veterinarian recheck the horse in one to two months to make sure there is satisfactory progress. You can increase weight gain in horses by offering them more good quality hay; feeding additional meals (lunch, bedtime snack); increasing pasture turnout (if forage is adequate); increasing caloric content of feed (add fat to the diet, e.g., corn oil, vegetable oil, rice bran, high-fat pellets); feeding beet pulp; and increasing the grain portion of diet (to not more than 50% of total ration). Thin horses should be fed separately to ensure they have adequate time to eat without pasturemates chasing them away from their feed. It might be necessary to decrease a thin horse's exercise to help him gain weight.

On a different note, beware of the hazards of having your horses overweight. Recent research indicates that horses that are obese--or have ever been obese--are at risk to develop metabolic syndrome. Laminitis can be a consequence of metabolic syndrome. If your horse has a cresty neck, poorly defined withers, and fat behind the shoulder and over the tailhead, he probably is overweight. Carefully evaluate the amount and type of grain you're feeding (remember that there are many definitions of the word "scoop"). Overweight horses are a special concern in the spring when carbohydrate-rich pasture grass is growing, putting them at increased risk to develop laminitis. If your horse is overweight, you should consider decreasing grain intake markedly, reducing the quantity of hay that you fed, increasing exercise, limiting pasture turnout or confining the horse to a dry lot, or using a grazing muzzle.

About the Author

Sally Vivrette, DVM, PhD, Dipl. ACVIM

Sally Vivrette, DVM, PhD, Dipl. ACVIM, owns Triangle Equine Veterinary Services, which is based in Cary, N.C.

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