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In contrast to nonstructural carbohydrates, structural carbohydrates must first be metabolized by the hindgut bacteria, converted into volatile fatty acids, which can then be used by the horse for various biological processes and to make glucose in the liver.
Starch is the high-energy carbohydrate consumed in feeds and is found in the leaves of young plants and grains. As plants mature, their starch content moves from the leaves into the seed heads where it becomes much more concentrated. Cereal grains, such as oats, wheat, barley, and corn, have about 45% to 65% starch content.
Interestingly, certain grasses will develop a seed head and can be an excellent source of high-energy starch at certain times of the year. Starch also can be a source of metabolic upset for horses that are sensitive to large amounts of it in the diet, and can lead to pathological conditions such as insulin resistance, colic, laminitis, developmental orthopedic disease, several forms of tying up, and Cushing’s disease if not well managed.
Cellulose and hemicellulose comprise the fiber or structural portion of forages. They are the main components of the leaves and stems of grasses and hay. Fibers such as beet pulp, rice bran, flax seed, and soybean hulls are being used with much more frequency in performance horse diets because they are energy-dense but are safer to feed than starch.
Glucose is the primary source of energy for the performance horse, but during peak aerobic activity the muscle cells will also use the fatty acids as a fuel source. Fats are a concentrated energy source for animals, providing 2 1/2 times as many calories as carbohydrates.
Fats are expensive compared with carbohydrates, but the increased energy yield and health benefits of reducing soluble carbohydrate in the racehorse’s diet are worth the extra expense. Also, horses that are adapted to a high level of fat in the diet will burn fat for energy and conserve glycogen longer than a nonfat-adapted horse. Horses that can spare glycogen during a competition will be less fatigued and may have more conserved energy to finish with.
Using fat as a fuel source creates less internal heat as opposed to the digestion and metabolism of carbohydrate-rich grains and protein. Equally as important, fat contributes energy without causing hyperactivity or excessive nervous energy produced from high-carbohydrate diets in horses that are sensitive to increases in blood sugar levels. Essential fatty acids in certain fats also provide the nutrients need to produce healthy and conditioned hair, skin, and hooves.
A well-balanced diet is essential for a horse to perform at optimum levels. Meeting nutrient requirements is the key to a good feeding program, as deficiencies and excesses of key nutrients, such as amino acids, vitamins, minerals, soluble and structural carbohydrates and fats will hinder growth, the performance, and the general well-being of the performance horse. Using products that are specifically formulated for the class of horse being fed is a surest way to guarantee the horse is receiving proper nutrient levels.
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Improving Bone Density
Bone is a dynamic tissue, constantly remodeling itself in response to the forces of impact and loading. Bones are made up of two types of bone tissue (fig 2). Cortical bone is the dense bone that gives bones their shape and strength. It makes up 80% of the adult skeleton. Trabecular bone is the ‘mesh like’ or honeycomb bone that forms in the ends of the long bones surrounding the bone marrow. Both types of bone are made up of a collagen matrix along with osteoblasts (bone producing cells) and osteoclasts (bone resorbing cells).
Collagen accounts for approximately one quarter of the body’s protein. It comprises 30% of mature bone as well as being a major component of connective tissue and cartilage.
Osteoblasts are bone forming cells that are interspersed throughout the collagen matrix. They secrete a ‘glue like’ mineralized substance known as osteoid which contains calcium and phosphorus.
Osteoclasts are bone resorbing cells. They work in unison with osteoblasts to remodel cortical bone. These cells are activated when cortical bone tissue is subjected to impact and loading forces. Remodeling increases bone density by removing existing bone and adding new bone to areas where the forces are greatest. Remodeled bone is stronger than modeled bone; i.e. the bone that is laid down during normal growth periods.
Although attention to conformation, foot balance and track design all play an important part in preventing bone injuries, increasing cortical bone density – in other words, building stronger bone is vital. This can be achieved through a combination of training and nutrition. written by: Dr Peter Gillespie. BVSc MACVS.
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Fig 2: Cross Section of Equine Cannon Bone.
S.s. - Trabecular Bone
S.c.- Cortical Bone
C.m.- Cavity containing Bone Marrow
Taken from The Anatomy of Domestic Animals; Sisson and Grossman.
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Summer '07
Benefits of using a higher fat/fiber concentrates over a traditional sweet feeds
- Horses exhibit stereotypic behaviors such as stall walking and weaving, as well as vices such as cribbing and wood chewing as a means to relieving stress.
- A large part of the problem can be attributed to the diet and feeding behavior of the stabled horse. Instead of grazing for 16-18 hours per day, the stabled horse may spend as little as 1-2 hours per day engaged in feeding activity.
- Many hours of non-feeding and idle time has been attributed to the occurrence of behavioral problems.
- Most horses in training are fed large quantities of grain (which contains a level of approximately 45-65% soluble carbohydrate, or, starch) in their rations because grains are traditionally more energy dense that forages. Feeding large amounts of grain can lead to starch overload in the hindgut and can result in metabolic disorders such as colic, laminitis, and insulin resistance.
- Feeding large amounts of grain is also associated with increased gut acidity. Some researchers believe that high grain diets cause low-level pain due to acidity in the gut which then serves as a stimulus for stereotypic behavior, in addition to gastic ulcer syndrome.
- Many horses with a propensity to tie-up will benefit from the addition of fat and fiber to the diet because it helps to lower the starch content of the diet, which may in turn decrease excitability and nervousness.
- Grain meal feeding is directly linked to an increase in seratonin, a brain neurotransmitter which modulates mood activity and alertness. High seratonin levels observed after eating meals high in starch has been implicated as the reason for sugar “highs” seen in some horses following a grain meal high in starch.
- Many other factors can affect behavior in horses such as sex, genetics, breed and environment, but it is fairly safe to say reducing starch in the diet of racehorses appears to play a role in improving mental and physical health of racehorses.
Dietary recommendations
- Grains are very palatable and high in digestible energy and should be incorporated in reasonable amounts in the exercising horse diet, as glycogen repletion and storage following maximal exertion is somewhat dependent on glucose provided in the diet.
- Ingredients like vegetable oils and soluble fibers, most notably beet pulp, soybean hulls and rice bran, do not contain high levels of starch and can be blended into the ration to help increase its digestible energy content without increasing the risk of starch overload.
Fats and fibers do not cause an increase in blood glucose when consumed, a biochemical reaction which in some horses seems to intensify the “sugar high” associated with feeding high grain diets.
Summer '06
In the summer months, it is useful to supplement electrolytes (minerals or salts) to horses that work hard enough to sweat profusely. Horses have a hypertonic sweat, meaning they lose more salts in their sweat than water. This is part of the reason why it is hard to get horses to drink water when they sweat - their thirst response is slow because the blood is actually dilute instead of concentrated with salt. This is the opposite of how humans sweat - our sweat is hypotonic.
Horses not working hard do not need extra supplementation above having free choice white salt sodium chloride and water available. For these horses, forage provides the electrolytes that are required (calcium, potassium, magnesium). Horses working hard and sweating a lot should be fed a quality electrolyte that lists all of the minerals previously mentioned as the first ingredients and perhaps a small amount of dextrose to help facilitate rapid absorption from the stomach into the bloodstream. Most important to remember is the horse must have access to water as soon as an electrolyte is fed or the blood becomes too salty. The whole purpose of the electrolyte is hydration, so water must be available in ample amounts to assist in hydrating the horse. Balance between the salts and the water is how hydration is achieved. If the horse is not worked and sweating on a particular day, there is no benefit to supplementing electrolytes that day. The extra salt will only cause the horse to drink more water to eliminate the extra salt. Therefore, electrolytes should be supplemented on need be basis only.
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