Horses, like people, have different metabolisms. Some can seemingly eat all they want and never gain a pound. Others appear to gain weight just by thinking about food. Horses who seem to absorb nutrients from the barest minimum of food are affectionately called “air ferns.”
The overweight horse and easy keeper have a filled-out frame, often rippling with fat over shoulders and rump. Usually, the neck has a prominent crest.
One of the most common reasons for obesity is the tendency of well-intentioned horse owners to over-indulge a horse with too much food. Excess calories simply turn to fat. While you might think you are feeding a “normal” diet, some horses are very efficient in the use of nutrients. If this is coupled with limited exercise, the relative abundance of food turns into fat. For a horse with pasture turnout, use a grazing muzzle to prevent intake of nutrient-rich pasture; otherwise, keep the overweight horse in a dry lot.
Horses plagued by musculoskeletal problems such as arthritis or laminitis might not be able to exercise; they often live a sedentary life. Such individuals need to be fed a diet restricted in fat, sugars, and carbohydrates, with reliance primarily on a high-fiber feed like grass hay. Alfalfa hay is very high in protein and energy and should be avoided.
Metabolic disturbances such as tumors of the pituitary gland related to aging, or hereditary issues like insulin resistance or equine metabolic syndrome (EMS) increase the risk of obesity. Your veterinarian can do endocrine testing to check for metabolic issues related to Cushing’s disease (pituitary over-activity) or to identify the possibility of EMS and insulin resistance.
A horse with insulin resistance and/or laminitis should especially be restricted in energy quality and quantity of his nutrient intake. Feeding grain products to such a horse is counterproductive because grain is poorly digested in the small intestine so it spills into the large intestine where it ferments and wreaks havoc with the digestive tract environment. Overgrowth of bacteria and subsequent release of inflammatory mediators set up conditions for circulatory disturbances in the feet, leading to laminitis.
To best manage amounts fed, invest in a scale to accurately weigh how much hay is fed as this allows control of the diet and your horse’s weight. Offering grains (corn, oats, barley) or senior feeds is detrimental as these feeds are loaded with calories. If a supplement must be fed, use low-starch/low-sugar commercial feed.
Usually, the best solutions to managing an overweight horse include exercise, exercise, exercise, in addition to feeding fewer groceries and limiting access to pasture.
By Nancy S. Loving, DVM