Equine Nutrition Education
A wide variety of equine nutritional topics was covered at the fourth annual Alltech Equine School April 25-28 in Lexington, Ky., sponsored by Alltech, a feed ingredient company in Nicholasville, Ky. Among the speakers was Harold Hintz, BS, PhD, Professor of Animal Sciences at Cornell University. He discussed possible directions of study for the next National Research Council (NRC) recommendations for equine nutrition (their current recommendations were published in 1989 as Nutrient Requirements of Horses, online at www.nap.edu/books/0309039894/html/index.html).
Currently, most researchers and nearly all feed labels in the United States use digestible energy (DE) to measure energy, but a net energy system might be more accurate. "If we change to a net energy system, we'd have to re-label all our feeds, supplements, and so on," he said.
Hintz also discussed other areas of equine nutrition in which more recent research has shown a horse's required nutrients to be slightly different than what the NRC recommends. Hintz concluded that, "New systems and new data demonstrate that it is clearly time for an extensive analysis and evaluation of energy and protein requirements."
Malicious Mycotoxins--Trevor Smith, BSc, MSc, PhD, of the University of Guelph, discussed mycotoxins (toxins produced by molds that can be harmful when consumed "in significant amounts" by livestock). Mycotoxins often act synergistically (amplify each others' toxic effects) when ingested together.
One of the best-known mycotoxins is the one produced by endophyte-infested fescue grass. Other mycotoxins can cause a loss of appetite, intestinal tract lesions, suppression of immune function, lethargy, ataxia (incoordination), leukoencephalomalacia or moldy corn poisoning, increased estrogen production, and/or decreased blood pressure in the horse.
One solution might be mycotoxin binders, which are large molecular weight polymers designed to bind to mycotoxins in the animal's digestive tract. They keep toxins from being absorbed, and help them pass out harmlessly in the feces.
Trace Mineral Requirements--Stephen G. Jackson, BS, PhD, discussed the roles of several important trace minerals in the horse and how much of them horses really need. "We've fed enough copper in the last few years to turn horses into pennies," he said.
When balancing a ration for any horse, Jackson stresses that you have to know the amount consumed and the nutrient and energy content of the forage before you can begin to look at supplements.
When you do consider supplements, consider this: "Two ounces of a common mineral salt will give you nearly half of a growing horse's requirements for salt, zinc, iron, manganese, copper, and iodine," said Jackson. "This is just another example of how you need to look at everything in the diet when looking at trace mineral needs. I try to formulate diets to meet needs without adding things."
Electrolytes and High Activity-- Electrolytes serve many functions, and must be adequately supplied to highly active horses. However, supplementation isn't always necessary. Stephen Cooper, BS, MS, PhD, Assistant Professor in Animal Science at Oklahoma State University, discussed the roles of various electrolytes.
"Sodium and potassium are not stored in the body, so heavy electrolyte supplementation before exercise may not prevent deficits," he said. "We're not coming close to meeting those (sweat) losses." While a horse might need 40 liters of electrolyte solution, you can usually only give at most three liters per hour. "This brings us back to dietary electrolytes to supply sufficient electrolytes," he said.
Skeletal Development in Young, Exercising Horses--"Unfortunately, the amount of research that has centered directly on the young athlete is quite limited," said Brian D. Nielsen, MS, PhD, Assistant Professor of Animal Science at Michigan State University. "We're forced to draw conclusions from older horses and combine them with growth studies from younger horses."
Higher protein is not the key to proper bone and muscle growth. One study found no significant benefits of feeding a diet with 20% protein versus 10%--however, there were problems with feeding more protein, such as high ammonia in stalls (a potential respiratory problem trigger), increased water intake for excretion of the extra nitrogen, and thus wetter stalls.
Minerals are also important, but one problem with calcium (Ca) and phosphorus (P) intake is that, "Many feed companies are balancing feeds to go with alfalfa hay," Nielsen said. Alfalfa hay has a high Ca:P ratio, so feeds balanced to go with it often have a very low Ca:P ratio. "But how many times do owners feed according to directions?" he asked. If horses have a diet with more phosphorus than calcium, they can get several bone problems.
Feeding Olympic Equine Athletes--Joe Pagan, PhD, MS, founder of Kentucky Equine Research and the official equine nutrition consultant for the 1996 and 2000 Olympic Games, discussed his observations on feeding and body weight in Olympic athletes. Horses lost weight on the endurance day, but gained almost all of the weight back by the next day because of plenty of post-exercise fluids given orally and/or intravenously.
He said that hay transport and storage was tough in Sydney because of different feeding practices in Australia, and quarantine restrictions made it tougher to import feedstuffs.
Feed Companies and Consumers--Steve Elliott, Southern Region sales manager for Alltech, discussed market concerns and trends. What affects the feeds people buy for horses affects those horses' nutrition.
The beginning is how much to feed. You can analyze two scoops of feed (which is hard to measure accurately), but "usually what the horse is getting is feed plus joint supplement, electrolytes, hoof supplement, vitamins and/or minerals, an extruded concentrate, and oil," Elliott said. "Add this to whatever size flake of hay plus whatever pasture the horse is eating, and you have no idea what that horse is eating. We need to communicate better on feeding."
Stabilizing the Equine Digestive Tract--Kyle Newman, BS, PhD, Director of Laboratories at Venture Laboratories, discussed equine gastric ulcers. The most effective treatment for gastric ulcers appears to be omeprazole, which inhibits the enzyme responsible for stomach acid production. Providing free, continuous access to forage to buffer acid production is also effective.
Yeast cultures in the diet have been shown to increase weight gain, decrease gas production, stabilize cecal pH, and increase pH (decrease acidity), helping minimize ulcers and gas colic.
Pathogens are another gut problem--one that could be minimized with compounds that can bind to pathogens and prevent them from attaching to the cells of the gut walls (and possibly decrease bacterial shedding). Mannan oligosaccharide (MOS) has been successfully used in studies to bind many strains of Salmonella and Clostridia bacteria, Newman said.
Nutrition and Disease
Feed manufacturers and others interested in equine nutrition attended "Advances in Equine Nutrition: Nutrition and Disease" sponsored by Kentucky Equine Research (KER), an equine nutrition, research and consultation company, April 30-May 1 in Lexington, Ky. The theme was how nutrition and various diseases correlate.
Research Developments--The seminar started with Pagan presenting some of the latest research from KER.
One study examined the effects of restricted hay intake on horses in high-intensity work or competition. Results showed that restricting hay intake to 1% of body weight can help decrease body weight, which will allow horses to expend less energy during exercise resulting in faster race times. (Remember, there are down sides to withholding forages.)
Another study showed that Thoroughbreds are more suited to high-intensity exercise than Arabians, while Arabians are better adapted to endurance exercise.
A third study showed that hydrating and rinsing beet pulp helps remove residual sugars, which results in a negligible glycemic (blood sugar) response, while the addition of molasses results in the same glucose response as that observed from feeding oats. Feeds that produce a low glycemic response might help horses which tie up.
In another study, KER discovered the zinc requirement in exercising horses was significantly higher than for sedentary horses. However, there was no difference in digestibility and retention for copper and manganese.
The final study that Pagan presented showed that the use of corn oil added to grain will delay gastric emptying. This delay might slow the rate of passage of the grain, allowing for more complete digestion.
Colic Management--Kris Purcell, DVM, of the Carson Valley Large Animal Hospital in Gardnerville, Nev., discussed the digestive tract, types and causes of colic, and how to minimize colic with feeding management. Purcell recommended the following tips to reduce the risk of colic:
- Match the horse's normal diet. Feed high-quality roughage as at least 50% of the horse's diet. Fat supplementation might be an option if extra calories are needed.
- Feed hay free-choice or feed small meals of hay and grain (if needed) often, and feed about the same time every day. Grain meals should be kept to three pounds or less.
- Provide daily or near-daily exercise.
- Make any diet alterations gradually, over a period of one to two weeks.
- Provide good-quality feedstuffs.
- Use only feeds formulated for horses.
- Allow free access to fresh water.
- Put the horse on a regular deworming program.
- Schedule regular dental care.
- Keep the horse's environment free of debris, toxic materials, and plants.
Managing the Underweight Horse--Kathleen Crandall, PhD, MS, East Coast Nutritionist for Kentucky Equine Research in Middleburg, Va., discussed management of the underweight horse. Discovering the reason why a horse is underweight is the first step toward correcting the problem. Reasons for weight loss include insufficient caloric intake, parasites, dental problems, disease, environment, herd dynamics, chronic pain, and physical problems of the digestive tract. Crandall recommended the following ways to put weight on a horse:
- Increase caloric intake.
- Check for dental problems. Have teeth floated regularly.
- Supplement fat.
- Feed a high-quality, early-harvested hay rather than a mature hay. Feeding an alternative source of fiber (i.e., beet pulp, soy hulls, wheat bran, or alfalfa pellets or cubes) might benefit some horses. Yeast and probiotics can improve fiber digestibility.
Molds and Mycotoxins--Mike Murphy, DVM, PhD, Associate Professor of Toxicology at the University of Minnesota, discussed diseases associated with mold that affect the guttural pouches, lungs, eyes, skin, reproductive system, and the body as a whole. He also discussed mycotoxins and effects that have been seen in horses.
Laminitis--Ric Redden, DVM, of the International Equine Podiatry Center in Versailles, Ky., discussed how nutrition relates to laminitis. Laminitis can be triggered by a variety of factors.
Redden discussed measures that should be taken to prevent laminitis, including not allowing horses to become obese and adjusting horses slowly to lush pasture. Monitor a horse which has been persistently lame for three to five days for any signs of laminitis. If laminitis develops, consult with your veterinarian and farrier to develop a proper treatment program.
OCD Study--Pagan presented a study that concluded feeding foals concentrates that produce low glycemic responses reduces the occurrence of osteochondritis dissecans (OCD). In the study, a high glucose and insulin response to a concentrate meal was associated with an increased incidence of OCD. He said that more research is needed to determine if the incidence of OCD can be reduced through dietary management.
Joint Supplements--Stephen Duren, PhD, a consultant for Kentucky Equine Research in Boise, Idaho, discussed the uses of oral joint supplements, also called nutraceuticals. Duren pointed out that nutraceuticals are not guaranteed to be safe. Label claims are not regulated. A study on joint products intended for animals indicated that 70% of products do not meet label claim. Also, the efficacy of most nutraceuticals is unproven by research. "Many horse owners are considering themselves scientists and making their horses research subjects," he said. Controlled research is now being done.
The Older Horse--Ray Geor, BVSc, PhD, Dipl. ACVIM, of R and J Veterinary Consultants in Guelph, Ontario, Canada, discussed Cushing's disease and dietary management to improve body condition and quality of life for the older horse. For the older horse which has dental problems, access to pasture is important. An alternative fiber source can help ensure adequate fiber intake, and fat supplementation can help add calories. Complete "senior" feeds might work well. Clinical signs of Cushing's include an excessively long and curly hair coat, weight loss, muscle wasting, lethargy, excessive sweating, bulging of the eye, an increase in fat deposition around the eye, increased appetite and thirst, and an increase in urine production. Various tests can be run to diagnose Cushing's disease; however, there is no cure, and the prognosis is guarded to poor depending on the number of complications that arise. Treatment can result in improvement in some horses. Due to an increase in susceptibility to infections, a top-notch preventive health program is necessary.
Neurological Diseases--Jon Foreman, DVM, MS, Dipl. ACVIM, of the University of Illinois, touched on four neurological diseases and how nutrition is involved in each.
Equine cervical vertebral malformation (CVM), or "wobblers," occurs mainly in young horses of large breeds as a result of a compression of the spinal cord. Affected horses have typically been overfed with higher than necessary levels of dietary energy, protein, or both. CVM can be prevented through careful breeding and feeding programs that avoid fast growth.
Certain breeds have been shown to have familial (genetic) predisposition to equine degenerative myeloencephalopathy, which involves progressive, neuronal degeneration. Some families of horses might have the tendency to absorb vitamin E poorly, and vitamin E is critical to neuron health.
Foreman pointed out that is has been recently shown that horses with equine motor neuron disease (EMND) have abnormally high copper concentrations in their spinal cords, showing that EMND might be related to high copper and low vitamin E concentrations in the diet. Greater exposure to green pasture should help prevent EMND.
Tying-Up--Stephanie Valberg, DVM, PhD, Dipl. ACVIM, of the University of Minnesota, spoke on how tying-up is linked to nutrition.
Horses which tie up sporadically have strained muscles, often caused by exercise that exceeds the horse's training level, but deficiencies of sodium, vitamin E, and selenium might also contribute to muscle cell damage. The diet should contain good-quality hay with little grain supplementation, salt, and a vitamin/mineral mix. In chronically affected horses, electrolyte and hormonal imbalances, lactic acidosis, and deficiencies of vitamin E and selenium have been proposed as causes. Fat supplementation has been shown to help. Valberg believes that one of the ways to manage polysaccharide storage myopathy is to decrease the amount of starch in the diet and to supplement fat.
COPD--Geor explained the relationship between a horse's diet and chronic respiratory disease. "A true food allergy in the horse is extremely rare," he explained, although recurrent airway obstruction, or chronic obstructive pulmonary disease (COPD), can be caused by allergies that are linked to dust from forages. In this sense, nutrition can play a role in the development of COPD. Geor encouraged people to soak--not just dunk--hay for horses with respiratory difficulties. Geor also discussed the importance of considering the water content at the time of baling to determine the hay's level of mold.
By Stephanie L. Church, Sarah Hogwood, and Christy West
POLL: University Equine Hospitals