What exactly does “metabolism” mean? By definition, it encompasses a wide range of biochemical processes involving nutrients and energy. Metabolism is influenced by hormones — most commonly, insulin (from the pancreas), cortisol (from the adrenal gland), thyroxine (from the thyroid), and leptin (from fat tissue).

Survival depends on metabolic hormones. Some correct blood disparities, others support the body’s adjustment to environmental changes. What we feed our horses, and the way we feed it, can either align with or run counter to what they instinctually know. The goal is to strive toward feeding horses in sync with their physical and emotional nature, thereby allowing for hormonal balance.


The equine digestive tract cannot tolerate periods of time without forage; it requires a steady flow of hay and/or pasture. There are several reasons for this:

  • The constant secretion of stomach acid increases the potential for ulcers.
  • The cecum must be full for digested feed and indigestible material (e.g. sand) to exit at the top.
  • The gastrointestinal musculature must exercise continually to prevent certain types of colic.

Horses who experience times with nothing to eat are in physical and emotional distress. Forage restriction is incredibly stressful.


Stress causes the adrenal gland to release the hormone cortisol. Cortisol tells the tissues to ignore insulin’s attempts to get glucose into the cells. Insulin increases to try to overcome this, but not very successfully (i.e. insulin resistance). When insulin is elevated, inflammation increases, and the cells hold on to body fat. And when body fat increases, it releases a hormone called leptin. Normally, leptin is a good thing, but not in this case.

The brain can become resistant to leptin. Under normal circumstances, leptin (secreted from fat tissue) goes to the satiety center in the hypothalamus portion of the brain to tell it that the horse’s appetite is satisfied. This is the body’s way of maintaining normal weight: fat increases, leptin rises, the brain says the body has had enough to eat, and weight stays within a normal range.

The excess body fat of obese horses promotes inflammation through the secretion of substances known as cytokines. Cytokines can damage the areas within the hypothalamus that recognize leptin. Leptin levels are high, but the brain is not responding (i.e. leptin resistance). Consequently, the horse keeps eating, getting more obese, producing more cytokines, increasing inflammatory damage to the hypothalamus, resulting in greater leptin resistance.


To do this:

  • Never let your horse run out of forage, even for a few minutes. Not only is free-choice forage feeding critical to his overall health, it also increases the metabolic rate. Feed appropriate hay and/or pasture that is low in calories, sugar, and starch.
  • Add a comprehensive vitamin/mineral supplement to hay-based diets. This fills in nutritional gaps and reduces the horse’s drive to overeat simply to obtain enough nutrients.
  • Feed whole foods free of additives and toxins. Whole foods can include beet pulp, alfalfa, hay pellets, copra meal, split peas, hemp seeds, ground flaxseeds, moistened chia seeds, blue-green algae, and various fruits and vegetables. Limit soybean meal — the long term impact of isoflavones (the phytoestrogen found in soy) on the thyroid gland is controversial.
  • Feed a variety of protein sources by mixing grasses and adding whole foods. When only one or two protein sources are fed, the excess amino acids can be converted to glucose, potentially increasing insulin.
  • Eliminate excess sugar and starch. These are found in sweetened feeds, cereal grains, wheat middlings, and rice bran. They raise insulin as well as triglycerides. Triglycerides can bind to leptin in the blood stream and prevent it from signaling satiety to the brain.

  • Avoid high levels of Omega 6 oils. These are highly inflammatory (e.g. soybean, vegetable, corn, wheat germ and safflower oils).
  • Increase Omega 3s. Feed ground flaxseeds or moistened chia seeds. Fish oils can be included in cases of high inflammation levels.
  • Add antioxidants. These include vitamins E and C, beta carotene (vitamin A), lipoic acid, grapeseed extract, green tea extract and spirulina, as well as herbs including turmeric, boswellia and ashwaghanda (which is particularly useful in combatting stress).
  • Avoid prolonged use of H2 receptor blockers and proton pump inhibitors for ulcers. They can interfere with the body’s ability to absorb nutrients, and create rebound acid production upon removal.
  • Add a probiotic for hay-based diets. Horses who graze on pasture will naturally consume a variety of microbes.
  • Allow for movement. Exercise increases insulin and leptin sensitivity and lessens inflammatory cytokines. It has also been shown to directly reduce hypothalamic inflammation. Keep stall confinement to a minimum.
  • Limit grazing muzzles. They can defeat the purpose if they cause stress. Limit their use to no more than three hours per day because the digestive tract needs more forage than they allow.
  • Consider slow feeders. Several should be placed in a variety of locations.


Stress launches your horse’s hormonal response into a state of imbalance. First, reduce his stress: unrestricted grazing on appropriate forage is paramount. (If necessary, use a slow feeder.) Second, feed him an antiinflammatory diet; and third, increase his movement. Your horse’s brain and body will regain health. This is the formula for success.


Juliet M. Getty, Ph.D. is an independent equine nutritionist with a wide U.S. and international following. Her research-based approach optimizes equine health by aligning physiology and instincts with correct feeding and nutrition practices. Author of the comprehensive resource book, Feed Your Horse Like a Horse and the topic-centered Spotlight on Equine Nutritionseries, available through her website GettyEquineNutrition.com.