Easier digestibility is among the benefits of using processed feeds over
sweet grain mixes.
by Amy Gill, Ph.D.
Feeding racehorses correctly is an art and a
science. One of the most delicate areas to balance is the safe feeding of horses that are in intense exercise
programs but also are confined to stalls and must consume high-concentrate rations to meet their energy
requirements. Often, racehorses require more than 50% of the diet as
concentrate to maintain body condition.
However, this type of diet makes horses prone to
gastrointestinal and other metabolic disorders such
as recurrent exertional rhabdomyolysis, or tying up. In addition, some horses are
sensitive to increases in blood sugar and often become
less tractable and excitable when fed high-grain diets.
In the past 20 years, nutrition
research has contributed to a better understanding of how to provide the racehorse with
sufficient nutrients safely and efficiently while
reducing the risk of causing metabolic and behavioral disorders. Some of the
most profound improvements include the use of concentrate rations that contain higher fat and fiber
fractions and the manufacturing of various combinations of feed ingredients that are processed in
various ways to stabilize and enhance the nutritional
value of the product.
Processed feeds, such as those that are
cubed, pelleted, steamed, flaked, cracked, extruded
(heated under pressure), or micronized (infrared waves heat and vibrate the starch molecule to
restructure or gelatinize it) are a good choice for
racehorses because they are more easily digested and absorbed in the digestive tract. In
addition, the starch in
processed grains is more readily absorbed before
it reaches the hindgut than that found in sweet feed.
This vastly lowers the risk of colic, laminitis, tying up, and other metabolic disorders related to
fermentation of starch in the hindgut.
Other useful alternative feeds include complete feeds that combine
fiber and concentrate in a pellet or cube, hay cubes, and pellets. Haylage, which is hay baled at a moisture
content of 50% to 60% and then vacuum-packed and fermented, is another interesting alternative feed available
Grain and Starch
The level of starch in the diet of racehorses is an area of
concern for managers. Straight sweet feed rations contain the highest levels of starch of all equine feeds,
generally in the range of 60% to 75%. Starch digestibility ranges between 87% and nearly 100% over the total
digestive tract, but the capacity for starch digestion and absorption in the small intestine can easily be
The rate and extent to which starch is digested in the foregut
(stomach and small intestine) in the horse is largely affected by several factors. These include the
structure of the starch granule, processing of the starch granule through heat and pressure, and other types
of feed present in the tract when starch is ingested.
The amount of concentrate fed at one time (single-concentrate
meals containing more than 0.4% of the horse’s bodyweight increase transit time through the small intestine)
also affects starch digestion due to reduced exposure to acids and enzymes available in the stomach and small
intestine. Starch that escapes digestion in the small intestine can alter microbial fermentation in the cecum
and colon (hindgut) and can lead to acidosis in the horse, a condition that might result in colic or
Acidosis occurs when soluble carbohydrates such as starch are
rapidly fermented, causing a rapid fall in the pH of the hindgut, which must be closely regulated to maintain
health of the microbial populations that reside there. A drop in pH in the hindgut causes rapid changes in the
types of microbes that are present, and abnormal alterations in the percentages of volatile fatty acids produced
Lactic acid production increases further due to increased lactic
acid-producing bacterial populations proliferating in the cecum and colon. Increased acidity in the hindgut
leads to mucosal damage, which leads to the release of histamine, an event that can precede the onset of
Additionally, many organisms in the hindgut that normally use
lactic acid as an energy source are highly intolerant of the acidic environment, and if these organisms die,
endotoxins are released and subsequently absorbed by the damaged mucosa. Endotoxins are vasoreactive
compounds that can lead to further complications associated with the availability of oxygen to tissues as
occurs during acute laminitis. Therefore, the digestion of starch in the small intestine is an extremely
important factor in the digestive health of racehorses, and safely feeding concentrated starch sources to
avoid soluble carbohydrate overload should be a focal point of all feeding programs.
Benefits of Grain
Processing of grains can have a significant effect on starch
digestibility in the horse. An investigation of the preilieal (last section of small intestine) digestion of
oats, corn, and barley starch in relation to grain processing showed that oat starch was most digestible,
followed by corn and barley. When the grains were simply rolled or crushed without heating, no improvement in
digestibility was seen but popping the grains (like popped corn) improved digestibility. The effect noted
through popping was probably due to the restructuring of the grain; the starch granules are altered and
partly disintegrated, which makes them soluble in water and more readily absorbed in the small
Another study examined the effect of corn processing on glycemic
response in horses. Glycemic response is a measure of the rise in blood glucose levels following a meal
containing starch. The effect of grinding, cracking, or steaming was evaluated using glycemic response as an
indirect measure of pre-cecal starch digestibility. Glycemic response was measured for each grain using a
glycemic index where the increase in blood glucose concentration was analyzed statistically and compared with
the rise in blood glucose that resulted from feeding cracked corn.
The greatest glycemic response and peak glucose was seen for
steam-flaked corn as opposed to cracked or ground corn. The results of this study showed that steam-flaking
corn increased digestibility of starch before it reached the hindgut (pre-cecal) more than cracking or
grinding. Higher peak concentrations of glucose indicate that steam flaking improved small intestinal starch
digestion, which is preferable to avoid starch fermentation in the hindgut. This result is considered
desirable from a digestion standpoint, but high glycemic response also has been linked to behavioral problems
in horses sensitive to elevated blood glucose concentrations.
Starch content of
The various grains fed to horses contain differing levels of
Oats: Oats are favored in grain mixes because they
are extremely palatable and are nutritionally compatible with the requirements of the horse. Oats contain about 53%
starch, 12% protein, 5% fat, and 12% fiber.
The horse, via enzymes secreted in the stomach and small
intestine, easily digests oat starch. About 83% of the starch in oats will be digested and absorbed in the
small intestine after ingestion of a grain meal that does not exceed 0.4% of the horse’s bodyweight, but oats
will cause and increase in blood glucose levels for about four hours after
Corn: Recently, corn has gotten a bad rap as a feed
ingredient for horses, and some of the scrutiny can be justified. Corn is very energy dense (high caloric content)
and should be used judiciously in equine rations. Corn contains about 71% starch, 8% protein, 4% fat, and only 2%
Unlike oat starch, corn starch is not digested at all in the
foregut unless it has been processed (ground, steam-flaked, pelleted, or extruded). Corn starch left
undigested in the foregut will proceed along the tract and become fermented in the
Barley: A hard-shelled grain that is not easily
chewed by horses, barley should be processed when included in concentrates. Often, barley is “rolled” to crack open
the hard seed coat when used in rations.
Barley contains approximately 60% starch, 11.5% protein, 2% fat,
and 5% fiber. Rolled barley has a low pre-cecal starch digestibility of about 21% in horses. Therefore, it
can be concluded that when grains are used in diets for horses, oats can be fed whole but corn and barley
must be processed before feeding.
Grain Mixes versus Processed
The composition of textured or sweet feeds can vary greatly from
those that are simply a mix of grains with a molasses content ranging from 4% to 12% to more elaborate mixes
that contain vitamin and mineral fortification. Straight grain mixes that are not balanced with a vitamin and
mineral pack can be dangerous to feed for extended periods due to imbalances and shortages of vitamins,
minerals, and protein required by the racehorse in training.
Sweet feeds are highly palatable to horses, help to cut down on
dust, and are useful when feeding supplements or medication. However, horses quickly consume sweet feeds,
which can contribute to lower digestibility in the foregut due to increased rate of passage. Molasses adds to
the sugar content of the feed and also to a rise in blood glucose.
Some textured feeds now contain inclusion of alternative soluble
fibers such as beet pulp, rice bran, and soybean hulls, which serve as energy sources that do not add to the
starch content of the feed. For those that prefer textured feeds, products containing soluble fiber and lower
starch are a much better choice because the fiber is fermented in the hindgut and will not cause digestive or
Pelleted feeds can contain high quality byproducts from the food
industry that normally would not be available to horses. However, it is difficult to identify ingredients in
pelleted feeds, which should only be purchased from a reputable manufacturer. Many of these high-quality
byproduct ingredients are readily available on domestic grain markets and are competitively priced as
compared to whole grains.
Wheat Middlings, a byproduct of flour milling in which the flour portion has been
removed from the wheat seed;
Brewer's and distillers grains a byproduct of the brewing and distilling industries
Corn gluten feed and meal. Corn gluten feed is the part of shelled corn that remains
after removing most of the starch, gluten, and germ. Corn gluten is similar but contains less of the
bran fraction found in corn gluten feed and contains slightly less
All these byproducts are relatively high in good quality protein
and are high in digestible energy.
Horses better digest pelleted feeds than sweet feeds due to the
heating of ingredients during manufacturing. Pelleted feeds contain title or no molasses and have a much
longer shelf life than sweet feeds. They are also easier to handle, with less clumping and caking in the
winter, and attract no flies in the summer.
Pelleted feeds do not cause much of a rise in blood glucose when
fed because heating helps to gelatinize or restructure the starch molecule, making it more digestible.
Additionally, many pelleted feeds contain highly digestible fiber sources such as alfalfa meal, soybean
hulls, beet pulp and rice bran, which are substituted for grain as sources of
One of the most important features of the pelleted feeds is the
inability of the horse to sort out the more palatable ingredients in the feed and leave the less palatable
but important components of the mix, such as the vitamin and mineral premix. Pelleted feeds are excellent for
horses that have difficulty chewing or are off feed because the feeds can be wetted and made into a
Steam extruded feeds are the most highly digestible of all
products available to the horse industry. The process of steam extrusion produces a stabilized product that
serves to preserve the nutritional value of all the ingredients used in the product.
For example. flaxseed meal is a popular conditioning supplement
used by many trainers at the racetrack. It is high in essential fatty acids, which provide nutrients needed
to produce healthy skin, hair, and hoof. They also are powerful antioxidants, which boost the horse's immune
Because essential fatty acids are easily oxidized when exposed to
oxygen, it is recommended that whole flax seeds be ground just prior to feeding to obtain the best
nutritional value from them. When ground flax meal is included in an extruded feed product, the essential
fatty acids are stabilized and preserved, eliminating the need for grinding just prior to feeding. Shelf life
can be three to six months, making extruded products extremely easy to store and feed as well as superior in
nutrition when compared with unprocessed feeds.
Processed forage that could be potentially be useful when feeding
racehorses is haylage, or grass silage. Haylage is produced by baling grass plants that are cut, partially
wilted until moisture content is about 50%, and then placed in a silo or container (usually a plastic bag)
where exposure to oxygen is eliminated. The plants use up the remaining oxygen in the bag, resulting in
fermentation, which causes a drop in the pH. At this point, the forage goes into a suspended state and
Haylage is very palatable and has a higher nutritional content
than traditionally cut and cured hay. Because of the acid pH produced by fermentation, good quality haylage
will contain little or no dust or mold.
Careful packaging is the key to making good-quality haylage
because if exposure to oxygen occurs after the grass is put in the plastic bags -- if the bag is punctured,
for example -- a second fermentation occurs and will cause spoilage in the areas of exposure. Because horses
consuming spoiled haylage could be in danger of contracting botulism, horses fed haylage should be vaccinated
for the disease.
However, the risks of problems from feeding good-quality haylage
is minimal. Correctly cured haylage can be a wonderful feed for racehorses. It is particularly useful for
horses that are sensitive or allergic to mold, pollen, and dust, such as those that are bleeders or suffer
from chronic obstructive pulmonary diseases or heaves. As many as 60% of the horses that are continuously
stabled are estimated to suffer from some type of respiratory disorder.
Complete feeds combine both the forage and concentrate portions of
the diet into one. Forages alone also can be processed into cubes and pellets. Complete feeds and
cubed/pelleted forages are convenient to use, especially when shipping, and they help reduce variability in
hay that often results when traveling.
Quality of ingredients in complete feeds and processed forages is
generally very high, so they have the potential to work nicely when formulating rations for
One source of concern in using this type of product with stabled
horses is the long period of time the horses have between meals without feed to consume. Complete feeds and
cubed/pelleted forages eliminate the need for extensive chewing of fiber, so the horse consumes them quickly.
The shortened time-frame required to ingest a meal could lead to long periods of boredom for the horse, which
may encourage the development of aberrant behaviors. This type of diet also may predispose racehorses to
ulcers, since acid production in the stomach continues after the conclusion of a
Processed feeds have greatly enhanced our ability to provide the
highest-quality nutrition safely to equine athletes. Though sweet grain mixes have had a stronghold on the
industry as a traditional concentrate feed for many years, the manufacturing technology present in the
industry today offers a superior product.
Convenience of use, higher digestibility through starch
gelatinization, high palatability, low dust/mold content, nutrient stability, and increased product shelf
life make the use of processed feeds in the racehorse diet a good choice.
Amy Gill holds a Ph.D. in equine nutrition and exercise physiology and is a freelance consultant and write.
Her areas of specialty include growth, exercise and metabolic disorders. Her email address is firstname.lastname@example.org
* Methods of Processing
Steam Extrusion: Ingredients used in the mix are
milled, steamed, pressure-cooked, and oven-roasted for a short period of time at carefully controlled temperatures.
The final product can vary in size but resembles dog or cat food nuggets.
Steam extrusion alters starch, protein, and fats, making them
highly susceptible to degradation by the digestive enzymes in the stomach and small intestine. Manufacturers
of steam-extruded feeds generally use heat-stable vitamins and minerals that are not affected during
processing. Steam-extruded nuggets are very stable and nutrients are protected from rancidity and oxidation
due to the nature of this type of processing. Most steam-extruded products contain only about 8% moisture,
which helps to prevent mold development, whereas grains are usually in the range of 11-13%
Dry Extrusion: Steam extrusion differs from dry
extrusion in that no moisture is added during the latter process, thus requiring much higher intensities of heat to
achieve gelatinization of starch. Unfortunately, this process causes some amount of heat damage to protein and loss
of vitamins and minerals.
Micronizing: In this process, infrared light waves are used in a
short burst to heat and vibrate the starch molecules to reconfigure their shape, making them more digestible.
When exposed to rapid internal heating, starch molecules swell, fracture open, and
Both steam and micronization afford the horse a better quality and safer feed that is less likely to cause
excitability. Research has shown that both of these processes can improve digestibility by up to 30% over ordinary
pelleted feeds. -- Amy Gill, Ph.D.