An easy keeper seems to absorb nutrients from the barest minimum of food; sometimes these horses are affectionately called “air ferns.” The overweight horse and easy keeper has 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 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 high-fiber feed like grass hay. Alfalfa hay is very high in protein and energy and should be avoided.
Metabolic disturbances--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; 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--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.