For a number of really good reasons, feeding fat has become of interest to horse owners. Fats and oils are added to horse rations to decrease dust, lubricate mixing equipment, help pelleting throughput, reduce segregation and encourage fat soluble vitamin utilization. Fat improves hair coat appearance, plus it is a great source of energy and has been associated with reductions in metabolic disturbances such as colic, ulcers and tying up.

If you divide a horse ration, the largest proportion will be for energy. Working, pregnant and growing horses often require more energy than what an all-forage diet will provide. That means you often must depend on a grain source to make up the energy shortfall.

Starch

In days past, a horse's diet consisted principally of forage. Today many horse diets will have a grain component, which is often 50 to 70 percent starch. This increases the calculated energy density of the diet. This is good; many horses have higher energy requirements than can be met on a forage only diet.

Horses have lower amylase activity than many other animals; they can handle starch, they just don't do as good a job of it as does a hog.

The extent to which starch is digested in the small intestine  depends on the source grain, processing, intake and individual horse variability. By and large, the starch from small grains is digested to a greater extent in the foregut than the starch from coarse grains.

Reducing the particle size increases surface area and increases starch utilization. As the amount of starch increases, the rate of passage increases; as rate of passage increases, more starch escapes.

As more starch escapes, you will start to see shifts in fluid balance, gut motility and reduced energy absorption. Starch fermented in the lower tract yields about 75 percent of the energy as starch used at the small intestine. Large grain meals can potentially cause a host of troubles: digestive upsets, laminitis, colic, etc.

Before all the blame is piled onto grain feeding, it would be prudent to note that rapidly fermentable carbohydrates are also found in pastures, particularly cool-season pastures in rapid growth. Usually the spring gives the highest levels at about 4 to 6 percent, but grass sugar levels can also be high in the fall, in the range of 3 to 4 percent.

The amount of starch that can be tolerated will vary with the type of grain and the type of processing; however, a general guideline is not to feed more than 0.2 percent to 0.4 percent of bodyweight as starch per meal. This can be challenging if you have animals with high energy requirements being fed once a day. Consider using a feed with oil such as MFA's Easykeeper.

Fat increases energy density

A means of increasing the energy of the diet without adding starch is to use a source of fat. Horses find oil more palatable than rendered animal fats; they will snarf up oil-fortified rations. Pound for pound, vegetable oil will have three times the energy of oats. Since fat does not ferment, you can add substantial amounts of energy without risks of laminitis.

While feeding high levels of starch will shift the site of digestion, you don't see that with fat. Fat has been fed at relatively high rates, with continued high digestibility and acceptability. Usually the constraints on the feed handling system or economics are reached before the nutritional upper level of fat feeding is achieved.

Fat reduces heat increment

The energy in fat-fortified horse diets is used more efficiently than the energy in low-fat diets. Adding oil reduces the amount of heat energy loss and increases the net energy available for production. This effect is mainly due to a reduced energy loss to the heat of fermentation. When the horse is under heat stress, this fat advantage becomes more pronounced.

Fat feeding affects behavior

There has been work done showing that reducing starch and feeding fat can alter horse behavior. Work in the 1990s at Virginia Tech indicated that feeding fat reduces the activity and reactivity of horses.

Fat improves efficiency

The effect of fat on foals and weanlings is an energy density effect. Young animals fed appropriate rations are more efficient and have faster rates of gain when fed fat-fortified rations.

Fat feeding and reproduction

Feeding fat to pregnant mares may improve reproductive efficiency by reducing the number of days open. When nursing mares are fed fat, the fat content of their milk increases, increasing the energy density of their milk. This gives faster rates of gain for the foal compared to foals whose dams where not fed fat-fortified rations.

Fat can spare muscle glycogen

There is an interest in some of the industry to elicit the best possible athletic performance from horses. With respect to horses that repeatedly perform high velocity activity of short duration, i.e. cutting, such horses on fat-fortified diets have demonstrated that feeding fat will have a tendency to spare muscle glycogen. This effect results in increased concentration of glycogen in the muscle of adapted horses.

Glycogen can be mobilized to produce energy under anaerobic conditions during short bursts. The storage and retrieval of glycogen is essential as the short term supply of energy when the animal hits oxygen deficiency during intense activities.

Sparing glycogen doesn't happen immediately upon adding fat to the diet; the horse needs to be adapted to the diet and conditioned for the event.