Excerpt from "Holistic Approach to Equine Practice,"
By Dr. Joyce C. Harman
A concise common sense discussion of various aspects of Equine Nutrition, including the following topics: Nutriton, Physiology of Equine Digestion, Water, Vitamins, Minerals, Antioxidants, Glandulars, Enzymes, Protein, Energy, Sources of Feed, Environmental Evaluation and Treatment of Performance Problems.
Published in Complementary and Alternative Veterinary Medicine: Principles and Practice (ISBN: 9780815179948), "Unit 8: Integration into Veterinary Practice," Chapter 33, pg. 601.
Holistic medicine is particularly applicable to the performance horse for several reasons. Holistic equine medicine considers the evaluation of the horse in its environment, including the rider, saddle, conformation, shoeing, training, and nutrition. This complementary approach to medicine not only accelerates healing times but restores the horse to optimal performance and health. The holistic modalities produce minimal or no side effects and no drug residues that would cause the horse to test positive in competitions and racing jurisdictions. With this approach, horses can reach their full potential because the whole animal may become healthier, not just a single part (the target for most conventional interventions). Horses can last much longer in competition because they are healthy and moving correctly. As the price of acquiring and maintaining horses increases, most owners keep their horses longer and do not treat them as disposable commodities. Currently, most leading equine athletes last 1 to 3 years in competition before they disappear or are downgraded significantly. Owners also wish to keep their horses longer for emotional reasons; more people seem to be connected to their animals on a deeper level or are at least acknowledging their emotional attachment as the "new age" movement gains momentum. This is evident as one reviews the lay magazines and books, which provide information on holistic approaches to health care, management, and training (Barnes, 1996; Bromily, 1994; Grosjean, 1993; Knight, 1996; Practical Horseman, 1995a, 1995b, 1996). Two veterinary periodicals also feature a column on alternative therapies (Jones, 1995-1996; Harman, 1994a, 1995, 1996).
In the racing industry, wastage through lameness and respiratory disease has been well documented (Jeffcott and others, 1982; Rossdale and others, 1985). In all of the horse industry, including racing, an enormous and largely undocumented wastage of horses results from performance problems. Many horses in all sports are bought as expensive prospects or are purchased while at an acceptable level of performance that later deteriorates. The traditional approach is to treat the horses with drugs and hope they improve; however, these horses rarely return to maximal performance and are usually sold at a reduced price. Many talented horses end up as school horses or in sale barns because of perceived behavior or performance problems. The results are losses of significant amounts of money, as well as frustrated owners.
A truly holistic approach to health requires making many changes, but the rewards are great. The weekend pleasure horse must be viewed as an athlete, as is the weekend rider. A complete holistic program for the horse involves the rider as well. Riders who are unhealthy or in pain may negatively influence their horses. Encouraging riders to heal themselves is often the most difficult part of the holistic health program, but it can also be rewarding. Practitioners must not forget to look at the whole horse and its environment.
Nutrition is the foundation of any holistic program. Without correct balance and availability of all nutrients, no horse can achieve maximal performance. The topic of feeding horses is generally surrounded by tradition, mystique, and many exaggerated claims. Horse owners have varying opinions on the type of feed to provide, but they are all still feeding the same equine species with the same digestive tract. Because horses are not food-producing animals, little money has been spent on equine nutrition research. As for equine nutrition from a holistic perspective, virtually nothing has been published and little research has been performed. One of the difficulties in conducting nutrition research from a holistic perspective is the complex interaction of nutrients. For example, in some cases, low calcium may be caused by another mineral deficiency or excess or the individual animal’s ability to absorb calcium. Basic studies of single nutrients improve our understanding of each nutrient, but more complex studies should examine the interactions between them. However, these studies will be costly and difficult to perform.
Horses evolved as foraging animals, grazing on whatever scrub, grass, and weeds were available. While foraging, horses move constantly, except for relatively short periods spent sleeping. If they became ill, a wide selection of herbs (weeds) were available to help solve their health problems. Today, commercialization of nutrition needs and rich, cultivated pastures have changed equine nutrition habits from rough forage to processed feeds and rich grass. Predictably, domestication and increasing levels of confinement for the horse occurred as humans became more "civilized." Moreover, increasing interest in new equine sports has created new demands on horses’ bodies and minds.
Physiology of Equine Digestion
In horses, food is processed through acid digestion in the stomach and fermentation in the cecum (Clarenburg, 1991; Swenson, 1977). The acid stomach absorbs water and begins protein digestion, mainly through the action of pepsin. Evidence suggests that some microbial fermentation of carbohydrates takes place in the stomach and small intestine (Alexander, Davies, 1963; Kern and others, 1974). The acid environment also ionizes minerals such as calcium, magnesium, manganese, and iron (Kimbrough, Martinez, Stolfus, 1995) to make them absorbable by the body; consequently, when acidity is reduced through the use of alkalinizing agents, those minerals are not readily absorbed (Hunt, Johnson, 1983; Mahoney, Hendricks, 1974; Mahoney, Holbrook, Hendricks, 1975; Oliver, Wilkinson, 1933). The acid changes pepsin to pepsinogen and triggers secretin, which triggers the release of pancreatic enzymes. The small intestine then hydrolyzes protein, fat, and carbohydrates into their final form for absorption. The fermentation vat, the cecum, is perhaps the most important part of the equine digestive tract. The cecum is designed to break down and ferment long-stem fiber and, through bacterial action, to produce vitamins and fatty acids. When the horse is fed mostly concentrates in the form of grain and little long-stem fiber such as hay, the incidence of colic is higher (Clarke, 1990; White and others, 1993). Horses should be fed frequently to keep the digestive tract full because they evolved to graze continually in the wild; the common practice of feeding twice a day can create digestive-tract illnesses and behavioral problems. Feeding meals primarily based on heavy grains causes significant fluid shifts, acid-base shifts, and changes in the microbial flora similar to those that occur in the rumen when excessive carbohydrates are fed (Clarke, 1990).
The intestinal tract contains bacteria and protozoa designed to digest food, manufacture vitamins, and make minerals available. These bacteria use dietary fiber in the digestive tract (Folino, McIntyre, Young, 1995) as an energy source. They live on the fiber and not in the intestinal wall; consequently, when fiber is deficient, the bacterial population is not healthy. The normal pH of the intestinal tract is acidic in the stomach and upper small intestine, becomes more neutral in the lower small intestine, and becomes close to neutral in the large intestine (Swenson, 1977), with microbial balance helping keep the pH in the correct range. Because bacteria inhabiting the intestinal tract are pH specific in their requirements for growth, they are found in places where the pH is correct for each bacterial species. The large intestine has a different vascular supply than the small intestine. The large intestine in the horse is basically a fermentation vat for the digestion of complex carbohydrates and a place for absorption of water and electrolytes (Swenson, 1977). "Pathogenic" bacteria normally inhabit the large intestine, but the immune system, along with mucus and fluids present in the large intestine, prevents these bacteria from becoming pathogenic in this location.
The small intestine is acidic and inhabited in part by the acidophilic lactobacillus species, a bacterium that controls its own reproduction by the excretion of lactic acid. If the environment becomes too acidic as a result of bacterial overgrowth or poor digestion, replication is slowed until the pH returns to optimum level (Clarke, 1990). If the pH stays too acidic, the lactate-consuming bacteria are adversely affected, causing an increase in lactic acid and consequent damage to the intestinal mucosa (Lupton, Coder, Jacobs, 1985; Moore and others, 1979). In the small intestine the vascular supply is much greater and mucus is produced as cytoprotection for the intestinal walls (Cepinskas, Specian, Kvietys, 1993), because this is the area for digestion and absorption of nutrients (Swenson, 1977). The tissues here are adapted to the acidic environment (Cepinskas, Specian, Kvietys, 1993).
When the digestive tract microflora become unbalanced, bacteria are not present in the correct proportions and incomplete digestion occurs. With incomplete digestion and poor-quality feeds, the pH can change, frequently becoming more alkaline. Motility can also change, allowing pathogenic bacteria to ascend from the large intestine, where the pH is alkaline, into the acidic small intestine. Intestinal mucosa may be irritated by gram-negative lipopolysaccharides, causing diarrhea. Alternatively, if the pH of the large intestine becomes more acidic and the acidophilic bacteria move down, the colonic mucosa may become irritated and produce pathologic signs (Mackowiak, 1982; Rolfe, 1984; Simon, Gorbach, 1986).
Much of the key to good nutrition is keeping the bacteria balanced in their proper places in the digestive tract. Just replacing bacteria in the form of a probiotic may not be the whole answer; if the pH is incorrect for the incoming bacteria, they will not be able to repopulate the gut as effectively. Substrates for bacterial growth and replication are supplied by a good natural diet high in insoluble fiber. The intestinal environment is a miniature ecosystem in which each player has a place and a job, and if any piece is out of place, the whole is affected.
Natural raw food has all the bacteria and enzymes needed to aid digestion; however, the processing of food may alter them. The healthy digestive tract, when functioning normally, can still digest high-quality processed food because healthy indigenous bacteria and enzymes already present in the digestive tract will continue to function. The unhealthy digestive tract has more problems functioning with poorer-quality feed. Live foods also appear to have other, as yet undefined, advantages that cannot be packaged or processed into a ration; overall health and hair coat quality are consistently better when animals are fed live foods as opposed to processed foods.
Anything that upsets the natural balance of the intestinal tract flora affects digestion and direct use of food. A course of oral antibiotics upsets the digestive flora balance and should be used only in specific, appropriate situations (Midtvedt and others, 1986; Schmidt and others, 1993). Overuse of antibiotics and nonsteroidal anti-inflammatory drugs has been shown to increase intestinal permeability, allowing food antigens and fragments of bacteria to enter the bloodstream; in some cases the resulting immune response leads to inflamed and arthritic joints (Bjarnason, So, Levi, 1984; Bjarnason, Peters, 1989; Darlington, 1991; Meilants and others, 1991). Antibiotics may also alter the immune system. Tetracycline inhibits the phagocytic ability of white blood cells, sulfonamides inhibit antimicrobial activity of white cells, and trimethoprim-sulfamethoxazole inhibits antibody production, according to a study carried out at the Stanford University School of Medicine (Hauser, Remington, 1982). Decreased thyroid function has been noted in dogs treated with trimethoprim-sulfamethoxazole (Hall and others, 1993). Reducing a fever pharmacologically may lead to slower recovery from infections (Doran and others, 1989; Jaffe, 1987). In cattle, oral antibiotics decrease the digestible energy (DE) of the diet by increasing the rate of passage of organic matter into the small intestine (Zinn, 1993).
A probiotic supplement with enzymes, bacterial substrate, and yucca should be given concurrent with or after any antibiotic therapy. The best probiotics are either a fermented product or a high-quality broad spectrum of live cultures. Few available live-culture products contain a good range of quality bacteria; consequently, many people believe probiotics are not helpful. However, overall health improves significantly with the use of appropriate probiotics.
Other factors that appear to disturb the normal digestive flora are frequent use of dewormers, illness, confinement, the stress of being worked during pain (a common occurrence today), and changes of diet. Dietary changes are in fact common because most feed manufacturers use least-cost programs to formulate feed, which means quantities of certain grains vary depending on cost. The final formula is still balanced for protein, vitamins, and minerals as listed on the label, but the proportion of each particular grain has changed. Prolonged stress may cause hypertrophy of the adrenal cortex, atrophy in the lymphatic system, and decreased intestinal integrity (Jefferies, 1991). Stress increases susceptibility to upper respiratory tract infections (Cohen, Tyrrell, Smith, 1991), depletes vitamin C, and increases urinary excretion of calcium, manganese, and pantothenic acid. The more horses are confined, stressed, and managed by humans, the more nutritional deficiencies and imbalances the observant veterinarian will find.
Water is the nutrient fed in highest proportion to any animal and the most often overlooked component in the nutritional program. By weight, horses consume 2 to 3 times as much water as food. If the water contains toxins, high levels of minerals, or any other unbalanced agent, nutritional problems will result. As has been widely reported in the media, water quality throughout the nation is suspect, even that of rural wells and springs far from polluted cities (Consumer Reports, 1990, 1993, 1996; Ritter and others, 1995; Worsnop, 1994). The quality of bottled water is often suspect as well; there have been reports of contamination and the marketing of municipal water as spring water (Consumer Reports, 1992).
Herbicides and pesticides are designed to kill plants or insects. A quart of one of these agents can treat many acres of land after it has been diluted; a product so dilute could be acting similarly to a homeopathic reagent. The dilution process involves much mixing (sucussing), and the solution is driven around in a tank through a bumpy field, shaking it up even more. The runoff then gets into our waterways and is mixed or sucussed more as it flows downstream. The waterways become large vats for these diluted combinations of herbicides and pesticides mixed together, and yet little is known about the effects of these chemicals in combination. A recent study showed that just mixing two environmental chemicals that function as estrogens (dieldrin and endosulfan) had 160 to 1600 times as much strength as either chemical by itself (Arnold and others, 1996). This study marks the beginning of our understanding of multiple chemical interactions.
Many horses live in areas with urban water supplies. Some stables give horses water considered unpotable for people. Increasingly, people are drinking bottled water; however, this is not practical for horses. However, use of excellent nutrition and detoxifying agents can help horses cope with the toxins. Clays such as bentonite absorb toxins in the gut (Schell and others, 1993, a,b). Nutritional supplements, as well as herbal and homeopathic treatments, can aid in the detoxification process. New products are coming on the market daily to help humans and animals adjust to our polluted world; however, most of these products have not been evaluated sufficiently to prove their efficacy.
Chloride is an important nutrient that has been found in excess in much of the water supply, most certainly in urban chlorinated sources (Troianskaia and others, 1993). Chloride is used in water disinfection. Evidence is mounting that chlorinated water is toxic and may contribute to or cause cancer in people (Flaten, 1992; Jansson, Hyttinen, 1994; Morales Suarez-Varela and others, 1994; Nelemans and others, 1994). No specific data are available involving its effects on horses yet, but similar associated disease is probable. Water consumption is influenced by mineral content – in particular, chlorine, potassium, and sodium – as the animal tries to maintain homeostatic balance (Brocks, 1995; Jordhal, 1995). Horses may not consume enough water for healthy hydration if the water is contaminated.
Water frequently contains excesses of a particular ingredient such as nitrates (Consumer Reports, 1990, 1996; Kross and others, 1993; Ritter and others, 1995; Worsnop, 1994). Nitrates can affect vitamin A and selenium absorption. Without vitamin A the metabolism of vitamins D, E, and the B complex vitamin is incomplete. Nitrates are implicated in some infant diseases and cancer (Senft, 1995). High nitrates are converted to nitrites in the cow’s rumen, converting hemoglobin to methemoglobin and creating an anemic state. In the monogastric swine, high nitrates may be irritating to the digestive tract. Neither of these effects have been documented in the horse; however, any substance that causes significant toxicity in one species probably causes some degree of toxicity in other species.
The best way to manage the potability of the water source is to test for toxins and high levels of minerals and chloride. Testing can be done through standard water analysis. Water filters of many sorts can be used, from simple charcoal filters attached at the spigot to complex systems attached to the main water intake for the farm. Consumer Reports (1993) published an excellent review of different systems.
A healthy digestive tract will manufacture water-soluble Vitamins – the B vitamins and vitamin C. Because many equine digestive tracts are unbalanced, they cannot manufacture sufficient water-soluble vitamins. This leaves the horse deficient and consequently more susceptible to illness. According to human and veterinary literature, stress also depletes the water-soluble vitamins (Gross, 1992), and certainly today most of our horses are under a great deal of stress. However, the answer is not just to start feeding a massive amount of these vitamins, because if the digestive tract is functioning poorly, the vitamins may not be used properly. Vitamins are also lost in the processing of feed (Pickford, 1968). As the horse industry moves more towards extruded and pelleted foods, more dietary deficiencies may become apparent.
Fat-soluble vitamins for horses are supplied mostly from food, except for vitamin D, which comes mainly from exposure to sunlight. Horses kept in stalls 24 hours a day and fed poor-quality hay may be vitamin D deficient because the main sources of vitamin D are sunshine, good quality hay, and supplementation (Abrams, 1979). However, vitamin D is sufficiently inexpensive to manufacture that almost all supplements contain some; if supplements are combined, an excess of vitamin D may result. Excessive vitamin D causes prolonged hypercalcemia by accelerating intestinal calcium absorption and bone resorption (Morita and others, 1993). Vitamin D increases intestinal calcium and phosphate absorption. Vitamin D regulates the coabsorption of other essential minerals, such as magnesium, iron, and zinc, as well as toxic metals including lead, cadmium, aluminum, and cobalt and radioactive isotopes such as strontium and cesium (Moon, 1994). Vitamin D may contribute to the pathologies induced by toxic metals by increasing their absorption and retention.
Vitamin supplements commonly contain plenty of vitamins and minerals that are inexpensive to manufacture (vitamins A and D for example) and low levels of more expensive ones (phosphorus). Balance is the key to proper supplementation, and natural sources are better than artificial ones because they are closer in composition to the food naturally eaten by animals. A few supplement lines meet these criteria; however, more are becoming available. Many of the higher-quality supplements combine quality vitamins, minerals, enzymes, probiotics, and herbs to achieve balance.
Mineral balance is perhaps even more critical than vitamin balance in the equine diet. A complex interaction occurs among many minerals; even a slight excess of one mineral in a diet may disrupt metabolism of other minerals (Fig. 33-1). Many of the trace minerals act as catalysts to help transform the major minerals into a form that can be used. Plants are good sources of trace minerals, and horses may seek out certain plants for their trace mineral content. Chemically fertilized soils that are farmed repeatedly (as most of our farms are) become depleted of trace minerals, so the grains grown on these soils and fed to horses are also depleted (Walters, Fenzau, 1996). Mineral nutrition then becomes extremely important.
A new branch of science called zoopharmocognosy involves the study of animals and their natural ability to select plants and herbs according to their needs and particular illnesses (DeMaar, 1993; Jisaka and others, 1993; Lipske, 1993; Robles and others, 1995). Horses naturally select from free-choice minerals as long as they are not too sick to sense their needs through instinct and odor recognition. Although conventional nutrition research reports that no species can accurately select free-choice minerals, some early research indicates that animals and children can self-select nutrients successfully (Al-Grecht, 1945; Barrows, 1977; Davis, 1934; Richter, 1943). Also, careful observation reveals that seasonal variations in mineral and vitamin consumption are significant. For example, when large areas of the Midwest were flooded in 1993, horses with free-choice selections of minerals and vitamins ate large quantities of B vitamins during the summer, when they would normally get most of the B vitamins they needed from the pasture. When horses' hair coats change in the spring and fall, horses offered free-choice sulfur along with other free-choice minerals eat extra sulfur, which is used in hair production (sulfur-containing amino acids). In the spring, when the grass is growing rapidly and is low in magnesium, horses consume extra free-choice magnesium, but they do not do this during any other time of the year.
Free-choice minerals should be fed with salt (provided separately from the salt supply). If both are fed together with salt in a mineralized salt block, the salt may limit the mineral intake. The average salt block, whether mineralized or plain, is designed for the rough tongues of cows. The mineralized block is generally 95% salt. If horses need minerals but not salt, they will not eat the mineralized block any more readily than a person would eat oversalted food. When horses are given plain minerals, the quantity they eat is often astounding (2 to 3 times normal intake) for a few months, until they have balanced out their minerals; then the amount consumed tapers off to a maintenance level of 1/2 to 1 ounce per day. For successful free-choice products, artificial flavorings, salt, and molasses should not be used because they may affect the intake of the nutrient.
One of the least understood minerals is calcium. Calcium is often given in excess to "help build strong bones." Calcium is also present in high levels in alfalfa hay. Still, many people want to add more calcium to a diet high in alfalfa. When a diet contains excess calcium, calcium metabolism is modified, leaving calcium in the bones and not absorbing it from the gut. Then, when the horse needs extra calcium (e.g., when performing in an endurance competition), the mechanism for supplying extra calcium from the bones is inoperative, causing calcium-deficient signs such as "thumps" or synchronous diaphragmatic flutter. Calcium is a key mineral; however, a so-called "calcium deficiency" problem may actually be caused by the level of available phosphorus. Phosphorus is an expensive mineral and therefore often deficient in supplements, whereas calcium is cheap and therefore commonly added as a processing agent in soybean meal to improve the flow. As a processing agent, calcium does not need to be included in the ration formulation, so the true amount of calcium in a ration may not be reflected by the calcium itself on the label. If the calcium added to the soybean meal was balanced properly with phosphorus, the cost of the phosphorus would be prohibitive. When phosphorus is added to the diet, calcium becomes more available in the blood as it is removed from bones.
A high concentration of iron in the water has an indirect effect on calcium and phosphorus. High iron levels impede the use of phosphorus, which in turn affects the availability of calcium. Therefore a calcium deficiency can actually be a phosphorus or iron problem. Moreover, because the transport of iron depends on a copper enzyme, low copper levels can prevent iron from being mobilized from its liver stores, causing anemia (Lee and others, 1969).
Balancing for deficiencies by adding an ingredient is a relatively simple procedure, but balancing for excesses is costly and requires extensive technical experience. Other ingredients must be increased to balance the one that is in excess. Steps can be taken to bind excesses, but few are successful. Clay can sometimes be of help by adsorbing minerals in the intestinal tract, allowing excess minerals to pass out in the manure.
In the author’s opinion, the best way to approach mineral nutrition is through a free-choice system, with the salt and mineral separated. Few companies provide a plain mineral supplement; usually, salt will be in the top half of the ingredient list. Avoid unbalanced single minerals or combinations of just a few minerals unless they are given free-choice (and are palatable for that purpose). Many products are formulated based on human requirements, which may not be appropriate for the nutritional needs of the horse. Racehorses are constantly given iron tonics to "build their blood," although most horses have normal iron levels. Several other mineral imbalances that can be important include (1) excess iron, which can tie up calcium; (2) calcium, which can inhibit zinc absorption; and (3) zinc, which can inhibit calcium absorption (Argiratos, Samman, 1994; Schryver, Hintz, 1982). Racehorses have more bone problems than other types of horses, and most are in a growth and remodeling stage of bone development (Schryver, Hintz, 1994), so deranged calcium metabolism could prove particularly detrimental.
Minerals occur in nature in all forms (acetates, citrates, sulfates) and are best if fed in varied forms. Chelated minerals are fashionable in mineral nutrition; however, they consist of a central metal atom and are absorbed by the body using only one mechanism. Complexing involves incorporating a mineral into the crystalline lattice of another substance that is not a metal. Absorption of a complex requires a different biochemical pathway. Although the terms chelation and complexing are often confused, the use of both in a formula is advisable, as well as all other types, such as citrates.
Antioxidants are receiving a great deal of press because considerable research in human nutritional medicine suggests the benefits of these nutrients. Free radicals are extremely reactive compounds containing an unpaired electron, and they have short half-lives. Free radicals readily bind with any available electron to become more stable; the available electrons may be found in the double bond in fatty acids of the phospholipid bilayer of the cell wall. The fatty acid then becomes a radical and requires another electron, which it acquires from the next fatty acid in the cell wall. This process eventually ends in cell membrane rupture and death of the cell (Toohey, Kreutle, 1995). Free radical damage from lipid peroxidation leads to brittle tissues, including loss of blood vessel integrity, poor circulation, and swelling of the legs. In some cases the lack of response to a well-selected treatment regimen may be attributed to a free-radical damage that leaves the tissue unable to heal properly. Refractory cases may respond clinically to coenzyme QlO and other antioxidants (Ward, 1995). When free radical scavengers are added to nutritional programs, the body gains valuable ingredients to support recovery from diseases involving pathologic inflammation (Nockels, 1988). Free-radical scavengers and antioxidants include MSM; vitamins A, E, and C; the carotenoids; superoxide dismutase (SOD); pycnogenol; coenzymne QlO; selenium; tumerin; and zinc (Toohey, Kreutle, 1995). Some horses need just one of these nutrients, whereas others may need all the antioxidants to affect the entire oxidation cascade.
Glandulars are nutritional supplements made from actual glandular tissue, often prepared with supporting nutrients. In small animal and human medicine, glandulars are used as replacement therapy for organs functioning sub optimally and as support for organs that show evidence of inflammatory or degenerative processes. Because glandulars are produced from animal sources, it is not "natural" for the herbivorous equine to eat glandulars, and some horses will refuse them. However, glandulars can be useful in equine nutrition and should be considered instead of synthetic hormone replacement, as in thyroid therapy or as support for other organs, such as the pituitary gland. Many glandulars are costly, especially for horses, which contributes to their infrequent use in equine medicine. For more information on glandular therapy, see Chapter 6.
Enzymes are present in organic, whole, raw foods in the correct amounts needed to digest that food. The problem comes when the food is grown under suboptimal conditions, processed, cooked, or otherwise altered. Most foods for horses have been grown on mineral-depleted, heavily fertilized soils and have been processed to some degree, denaturing many native proteins and enzymes. In a normal, healthy intestinal tract, enzymes are produced by indigenous bacteria (Mitsuoka, 1992), and the enzyme reserves are sufficient for normal digestive processes to handle cooked or processed food. Because many horses exhibit suboptimal digestive function, equine patients often improve significantly when digestive enzymes are added to their diets.
The addition of enzymes to the food is controversial, because many nutritionists believe that enzymes are digested in the stomach and cannot reach the small intestine where they function. However, some research suggests that peptides and some intact proteins are passed through the stomach and absorbed from the gut in active form (Gardner, 1988; Sanderson, Walker, 1993; Walker, 1981). One study of chickens fed an enzyme-supplemented diet showed higher apparent ileal digestibility of organic matter, crude protein, starch, fat, and dietary fiber, indicating the efficacy of enzymes (Frigard, Pettersson, Arnan, 1994).
Enzymes may prove helpful in the treatment of certain viral conditions such as herpes zoster in immunosuppressed patients (Jaeger, 1990), and the immune deficiency of AIDS has been ameliorated with enzymes (Stauder and others, 1988; Wolf, Rosenberg, 1972). Enzyme supplementation is routinely used in the treatment of pancreatic disorders, mainly insufficiency problems (Goldberg, 1992) but is now being investigated for a wider variety of uses (Prochaska, Piekutowski, 1994). Many veterinarians have also seen improvements in skin conditions, especially in atopic dogs. At this writing, no controlled studies of enzyme therapy in horses have been reported, although enzyme supplementation has been used for horses with poor hair coats and digestion, with good results. Enzymes tend to be expensive supplements, although they are valuable in selected cases.
According to National Research Council (NRC) nutrition tables, adult horses require only 7.5% to 12% protein in their total diet, including all grain, hay, and forage. The lowest percentage of protein in commercial feed available is 10%, and protein levels of 14% to 16% are common. Because horses have evolved to eat mainly roughage, no physiologic reason exists for these high protein levels. High-performance horses are routinely fed more grain, so an accompanying increase in simple volume of food usually provides for any extra protein requirements in this population. Some horses, especially older animals, do seem to have a greater protein requirement and may benefit from its addition to their diet.
Besides being expensive, providing excess protein is one of the more harmful practices in feeding horses. In the cattle industry the ill effects of excess protein have been well studied, yet farmers still feed too much of it. In cattle fed excess protein, ulcers and poor digestion result, and although ulcers have not been studied in relation to protein levels in the horse, this association may merit further study.
In the horse industry, people spend a lot of money trying to combat the ill effects of excessive protein in horses. Some of the ill effects include anxiety or tenseness, difficulty in riding, swollen hind legs, problems with maintaining weight, liver and kidney disease, soft feet and frogs, and a poor hair coat. Research has documented many ill effects of excess protein intake in the horse (Box 33-1).
Increased water intake, urine volume, sweating, urea in sweat and urine, plasma urea levels, and postexercise orotic acid excretion have been noted (Freeman, 1985; Hintz, 1980, 1987; Meyer, 1987; Miller-Graber and others, 1991; Slade and others, 1975). Because of these factors, early dehydration and thirst may limit endurance performance (Glade, 1989). No beneficial – and some detrimental – effects in the performance of racehorses and endurance horses are seen, including higher heart and respiratory rates in endurance competition, early fatigue in endurance horses, and slower racing times in thoroughbreds (Glade, 1983; Hintz, 1980; Miller, Lawrence, Hank, 1985; Slade and others, 1975; Smith, 1986). Lower muscle glycogen concentrations and increased blood ammonia concentrations are also seen with excessive protein in the diet (Meyer, 1980; Miller, Lawrence, Hank, 1985; Pagan, Essen-Gustavson, Lindholm, 1987). Increased urinary calcium and phosphorus loss with excess protein (Glade, 1985) may contribute to some of the developmental bone diseases seen in horses; many young horses are fed extremely high levels of protein.
Plant protein byproducts such as soybean meal are energy deficient because the oils are removed through a toxic solvent process. Feeding soybeans may contribute to incomplete digestion. Urea breaks down instantly, whereas soybean meal takes longer; both can be toxic to horses when fed in excess.
Alfalfa hay is extremely high in protein (15% to 22%, average 17%), perhaps because excess nitrates (nitrogen) are used as fertilizer on the fields. A level of 12% is considered poor quality, although this is a healthy level for alfalfa; 20% or higher is considered good, but it is dangerously high for horses. Recall that the equine dietary requirement for protein is 7.5% to 12%. If samples of alfalfa hay are taken from the field in the early morning to test for nitrogen content, the plant is still covered with nitrates from its own overnight metabolic process. It is not until the sunlight converts the nitrates into plant tissues that a true reading is obtained. The laboratory analysis may show the hay as up to 5% higher in protein than it really is. Feeding alfalfa hay from nitrogen-fertilized fields makes it extremely difficult to achieve a correct protein level in the diet.
Horses eating good-quality pasture grass or hay generally take in all the nutrient energy they need from forage. Concentrates (grain) are needed only to provide extra energy (calories) required by the horse to perform stressful work and maintain weight. Owners have an obsession with feeding grain, even to fat horses, on the basis of the mistaken belief that grain is necessary to balance the diet. However, provision of grain is necessary only to maintain a healthy weight. Balance can easily be achieved without grain by using forages and a balanced supplement, although a small amount of grain is an excellent way to persuade a horse to come to the barn regularly. A horse at proper weight should have barely visible ribs; most show horses are well over 100 pounds overweight.
Much information is available concerning the overfeeding of foals and the resulting developmental orthopedic diseases. It is common practice to start a foal’s life by creating obesity. Foals receiving proper nutrition, especially with regard to minerals, are better able to tolerate being overfed without developing problems and are much less likely to develop problems if they are not overfed.
Sources of Food
Horse feeds are becoming more and more processed, to the extent that some extruded feeds resemble dog food and probably have as many nutritional problems as commercial dog food. Many feed companies use "least cost" means to select ingredients, so quality and content can change from batch to batch. Cleanings and fines from cracked com make up a portion of the grain used in commercial feeds, and molasses is added to reduce dust, satisfy the demand of horse owners for a sweet feed, and increase palatability of ingredients such as soybean meal.
Sugar is as bad for horses as it is for any other species, and horses may exhibit mood swings similar to those seen in humans. In my clinical experience, horses calm rapidly and consistently after molasses-sweetened feeds are removed from their diets. Molasses also contains chemical preservatives and often propylene glycol as a surfactant. If sensitive to preservatives or propylene glycol but not to the sugar content of molasses, the horse may eat human food-grade organic molasses with no problems. Some other chemicals allowed as preservatives to guard against fermentation of sugars in feed-grade molasses are sodium benzoate, calcium propionate, and acetic acid, in levels from 2 to 20 pounds per ton depending on weather conditions. One study showed a significant rise in blood sugar after the consumption of sweet feed, with a corresponding drop in blood pH (Ralston, 1992). Although the authors drew no conclusions as to the effects of these fluctuations, such changes might have significant effects on the horse’s body and behavior.
Pelleted feeds are used as an alternative to sweet feeds and do not cause the characteristic increase in blood sugar of sweet feeds. However, poor-quality feeds are easily disguised in pellet form. Some horses eat pellets too rapidly and may choke; others may be slightly dehydrated, causing pellets to form a blockage in the esophagus.
The best feeds are oats, barley, and corn with no added molasses and, perhaps, beet pulp. Availability of quality grains is a problem, especially with barley, which is used in England as a staple equine food. Corn may contain aflatoxins in certain areas. A mixture that works well consists of 25% large cracked or flaked corn; 30% steamed, rolled barley (the only form available in bulk); and 45% oats (large racehorse oats or crimped oats). Any combination can be used in a given area of the country. Contrary to popular belief, Corn has the lowest heat of digestion of any grain because corn contains less fiber and more DE than any other grain (National Research Council, 1989). Corn is an excellent summertime horse feed, particularly for equine athletes requiring endurance because of the low heat of digestion. Beet pulp is a useful food and can be substituted for bran in the commonly used bran mash. Beet pulp is a good source of minerals, carbohydrates, and fiber (National Research Council, 1989).
Fats are commonly added to equine diets. Most fats in horse feed are probably preserved with chemicals routinely used in dog foods and are extracted with a solvent process. Holistically minded owners should be encouraged to buy cold-pressed corn oil to supplement the feed. The best source of vegetable oils is from the plant itself, and providing a bit of extra corn is an inexpensive way to feed oils.
Pasture need not be lush and chemically fertilized to provide the energy needed for horses. Excellent grazing can be obtained from pasture with herbs (weeds) mixed with the grass; this combination allows the horse to select plants other than grass for both nutritional and medicinal reasons. Horses with all-day access to lush pastures tend to be fat. On the other hand, many horses are never turned out to pasture. These horses miss not only the movement that helps digestion and the sunlight necessary for vitamin D formation, but also the chiropractic benefits of stretching, rolling, swatting flies, and the like. Perhaps the biggest benefit of pasture time is the mental relaxation.
Hay forms the bulk of the horse's diet in winter and, in some areas of the country, year-round. Fiber stimulates the intestinal mucosa and muscle in the presence of healthy intestinal flora (Goodlad and others, 1995). The horse's "fermentation vat" (cecum) needs long-stem fiber and not chopped fiber such as that provided by finely chopped hay cubes. Digestion of short-stem fiber takes place primarily in the small intestine, leaving the cecum less full than it should be. Some parts of the country have only alfalfa hay, which is too high in protein and calcium. A variety of hay is the best, combining some grasses with some legumes; balance is the key. A horse is meant to eat long-stem roughage for about 20 hours a day, not in two small meals of rich hay. Ideally, herbicide-free hay grown in mineral-rich soil should be fed.
Horses receiving adequate nutrition have fewer health problems, recover from disease faster, are more resistant to contagious illnesses, and are better able to maintain physical condition.
Horses are herd animals and move 20 hours a day in nature; when a horse is confined to a stall for 23 hours a day, ridden for 1 hour, and returned to the stall, behavioral and health problems may result. Some horses exhibit repetitive-motion disorders such as cribbing and weaving. Most horses with these disorders behave normally when they have access to open fields and companionship, although some persist in their bad habits. Most show horses in all disciplines express their dissatisfaction with over-confinement by being tense, nervous, or difficult to ride. Other horses become aggressive or difficult to manage. Most horse-show clients are looking for drugs or, more recently, natural products to slow their horses down and make them manageable because they refuse to turn them out to play and persist in feeding too much grain, often laced with molasses.
The horse's environment, feeding habits, water situation, and turnout should be carefully observed. Horses who are bored or infrequently fed are more likely to experience problems. Choking from eating too fast and colic are much more common in stall-kept horses (White and others, 1993).
Stable air quality is another way in which the environment may affect horses adversely. Ammonia is often present at toxic levels, but owners and stable help become accustomed to the smell and may not notice it. People generally notice air and odors more in the aisleway of the barn because they do not smell the bedding at ground level, especially after a horse has spent 12 or 15 hours in the stall. Horses spend a lot of time with their head on the ground, even those fed from a manger. Ammonia is toxic to lung tissue at a level of 10 parts per million (ppm) (do Pico, 1992). This is the level at which an odor can just be detected. At 30 ppm a person’s eyes will water. Ammonia in the air has been shown to increase bacteria and fungi in lungs (Kastner, 1989; Walthes, Johnson, Carpenter, 1991). Air-circulation studies in English barns point to increased ammonia and dust as significant factors in the development of allergic lung disease such as heaves (McPherson and others, 1979). Ammonia levels are much higher in urine from horses fed excessive amounts of protein (Hintz, 1987; Lawrence, 1994); consequently, high-protein feeds can increase the odor and toxicity of ammonia in the air. High-nitrogen urine can be identified by the appearance of yellow, dead grass at each urination spot.
Horse owners frequently install overhead automatic fly-control systems designed to spray insecticides at regular intervals. Some of these units are set to spray every 15 minutes, filling the air and covering feed, hay, and water with insecticide. Under these conditions, horses are not only breathing the insecticides but also ingesting them. These pesticides are for use in non-food-producing animals, so the long-term effects of these compounds have not been thoroughly investigated. Humans are exposed to the pesticides as well; most barn owners using these systems stand directly underneath the sprayers, not realizing the potential for adverse effects. People may leave the barn to get relief, but horses are confined to their stalls and are forced to breathe the chemical mist.
Barns are kept closed for human comfort. New barns are often built and covered with Tyvex (house wrap) to seal out all drafts; ammonia buildup occurs rapidly in this situation. The ideal barn has stalls open to the outside, wide spacious aisles with good air circulation, and partial doors, gates, or stall guards to allow air circulation at the most critical place-the floor. Other ways to improve existing structures are as follows:
• Open doors and windows, closing them only long enough to do barn chores. If the weather is bad, open the door opposite the prevailing wind so air can circulate without causing the contents of the aisle to blow away.
• Clean the urine spot out of the stall every day. Many people let the urine build up, then strip the stall occasionally. Ammonia builds up at floor level but may not be detectable to humans.
• Consider the bedding. Straw is not absorbent; consequently, ammonia levels become toxic....
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Treatment of Performance Problems
Treatment of performance problems requires a whole-horse approach to be consistently successful. The saddle sits on one third to one half of the acupuncture Bladder meridian association points; consequently the rider and the saddle have a significant effect on the flow of Qi, or energy, through the body. Qi affects the health of many parts of the body. For example, pressure points often occur at the cantle, caused by the saddle or the rider. These points put pressure on some of the association points related to the meridians that traverse the hind leg (BL-18 through 22). Many horses with chronic back pain have hind-leg lameness or stiffness, and treating the problem locally, whether with conventional therapy or with acupuncture, only palliates the problem. Using a whole-horse approach reduces the need for many repeat treatments. Failing to examine all aspects of the horse and rider is one reason that acupuncture and chiropractic have the reputation of providing only temporary results.
The rewards of looking at the whole horse are great. The challenge is to determine the pieces of the puzzle that need attention and then whether the pieces can work together. When the practitioner considers the whole horse, corrects saddle fit, analyzes the rider's position, and helps the horse learn new behaviors, the results often far exceed expectations and last for a long time. Owners are pleased, and practitioners are rewarded not only with faithful clients but also with many referrals.
I would like to thank Jim Helfter for this assistance in researching equine nutrition and Ann Harman for editing and proofreading the manuscript.
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