AAEP Convention: Nutrition
Recent Developments in Equine Nutrition
A lot has happened in the field of equine nutrition research in the last five years. Ginger Rich, PhD, of Rich Equine Nutritional Consulting in Eads, Tenn.; and Leslie Breuer, PhD, of LH Breuer and Associates, updated veterinarians who attended the Current Concepts in Equine Nutrition in-depth session at the convention. Not all of the research done from 1998-2002 could be included in their presentation titled "Recent Developments in Equine Nutrition With Farm and Clinic Applications," so Rich and Breuer chose what they felt were some of the most important research findings.
To organize their presentation, they divided it into 11 topics--water; energy; minerals; protein; vitamins; growth; broodmare nutrition; performance horse nutrition; nutritionally related diseases; new products, ingredients, and processing methods; and miscellaneous topics. (For topics not included here, see article #4116 online.)
Research at New Bolton Center determined that during the winter when warm and cold water are both available, a horse will prefer to drink the cold water, but in lesser amounts than if only warm water were available. When provided with either warm or cold water, horses will consume more warm water than cold water. Therefore, in order to get a horse to drink more water during the winter, lessening the risk for dehydration, only provide warm water. In addition, researchers observed that confined horses drank the most shortly after a grain meal or within an hour of eating hay. It is suggested that lack of water availability during this time might contribute to poor performance or colic.
In a Kentucky study, it was found that resuming exercise delayed further absorption of water. Geldings performed in a simulated endurance training exercise to determine if high-intensity exercise influenced fluid uptake from the gastrointestinal tract. During a one-hour rest period, some water was absorbed and rehydration began. However, when the horses resumed exercise, exercise then delayed absorption. Rich said there is a risk of colic and founder when hot horses drink cold water, then stand around. Rich recommended that hard-working horses in prolonged exercise be allowed periodic rests of at least one hour with free access to water after a cool-down period.
In other research, feeding fat to performance horses has been shown to have beneficial effects on water retention and water available for sweating, which allows better heat dissipation during hot, humid weather.
"In the past five years, there has been abundant literature on bone mineral content, availability of organic versus inorganic sources, emerging significance of previously considered minor minerals, and effects of growth, exercise, or sedentary status on mineral metabolism," Rich said.
She mentioned the use of a biopsy of the twelfth rib as a diagnostic tool in evaluating mineral status, especially calcium. In addition, computed tomography can also estimate bone mineral content and differences in bone density.
Chromium--This mineral is not well understood, but a new study has shown that chromium tripicolinate supplementation can increase the rate at which glucose is metabolized. However, further research failed to show an effect on growth rate and development in yearlings, and there was little effect on metabolic, hormonal, and immune response in mares fed a Bermuda grass hay diet. In addition, supplementation of growing, sedentary, and geriatric horses with chromium tripicolinate or chromium-L methionine had no consistent effect on growth, immunity, or glucose/insulin responses.
Molybdenum--Despite reports in other species of a detrimental effect on copper absorption and retention with molybdenum supplementation, horses seem to be immune to this.
Aluminum--Short-term addition of aluminum to the diet did not affect the digestibility and mineral metabolism of calcium, phosphorus, magnesium, zinc, copper, and boron.
Silicon--In a study involving young Quarter Horses in race training, zeolite A, a silicon-containing supplement, was fed. Researchers found less bone-related injuries in the supplemented group. In addition, supplemented yearlings had increased plasma silicon concentrations and decreased bone resorption. However, the study did not determine if bone strength was improved. Rich said that there seems to be promise in supplementing injured young horses with silicon.
Iron--Liver biopsies of horses fed excessive amounts of iron as ferrous sulfate showed no abnormalities. Therefore, it was concluded that horses or ponies are unlikely to develop iron toxicosis by over-consumption from this source of iron.
Manganese--One study confirmed that horses require the level of manganese recommended by the National Research Council (NRC). This level is 40 ppm, and Rich said that horses in regions known to be deficient should be supplemented. In the study, horses receiving 40 ppm gained more weight, had better feed efficiencies, higher serum copper, higher serum hydroxyproline (an indicator of bone resorption), and a higher total bone mineral content than those fed a diet deficient in manganese.
Copper, Zinc, and Manganese--A study comparing exercising horses to sedentary horses supplemented with copper, zinc, and manganese found that exercising horses have an increased need for zinc. Exercise had no effect on the digestibility or maintenance requirements of copper and manganese. Rich said that National Research Council (NRC) values for zinc in working horses might be underestimated.
According to Rich, replacing half of the inorganic form of copper, zinc, and manganese with an organic form (also known as chelated or proteinated) in the diet did not affect liver concentrations of these minerals, did not improve immune response, and did not improve hoof wall growth rates, hardness, tensile strength, or trace mineral content in the hoof. Replacement in broodmare diets was not beneficial. In general, it was found that inorganic forms of these minerals were just as effective as organic forms.
Another study found that organic copper and zinc might increase copper and zinc retention and have slight benefits for copper digestion.
Selenium--Inorganic and organic forms of selenium were compared in exercising horses. The inorganic form of selenium-enriched yeast was more digestible with greater retention than sodium selenite.
Calcium, Phosphorus, and Magnesium Involved in Bone Density--Horses which have been confined to a stall or deconditioned for at least 12 weeks with minimal exercise experienced a decrease in bone mineral content. Supplemention at twice the currently recommended calcium level made no difference. "After 12 weeks of stall confinement, loss of mineral content might have weakened bones," said Rich. "Great care should be used in the reconditioning process to avoid skeletal injuries."
Further research found that higher levels of calcium and phosphorus in the diet allowed greater bone turnover in all ages, but young animals have the highest turnover. According to Rich, inactivity results in lower bone density, and when exercise begins, there is an increased risk of injury in older horses.
A study done at Rutgers showed that supplementing weanlings with 10 grams per day of vitamin C and 800 international units (IU) per day of vitamin E after a long trip improved vaccine response, reduced upper respiratory infections, and reduced days that they were off feed compared to non-supplemented weanlings. Another study found serum ascorbate and tocopherol concentrations were higher in horses that had been supplemented with vitamins C and E. Rich recommended that performance horses receive supplementation.
Another study found that oral and natural form d-alpha-tocopherol was the most effective form of vitamin E.
Another time for supplementation might be for broodmares and foals. Broodmares lacking vitamin A--such as those on a dry lot or with poor-quality hay--are likely to have foals with lower birth weights, slower growth, an increased chance of foals with congenital contracted tendons, and an increased risk of retained placenta. One study showed that supplementation with retinyl palmitate at twice the NRC values resulted in higher pregnancy and foaling rates. Mares did not respond well to water-dispersible beta-carotene.
Rich recommended that lactating mares and foals be supplemented with folate (folic acid) until the foal is three months of age, since it has been demonstrated that mares' milk folate levels decline during the first three months of lactation, leaving foals deficient. However, when foals begin to eat forage, their folate levels go back up.
Rich discussed how vitamin K is important for blood clotting and bone growth. She said horses might have enough vitamin K in their diets for blood clotting, but lack enough for proper bone metabolism.
Growth and Development
The current trend in the horse industry is to accentuate growth in young horses; however, some fear developmental orthopedic disease (DOD) if growth is too rapid or foals become too large. Additional support for this theory was obtained in recent research done on a Kentucky Thoroughbred farm in which 271 foals were evaluated over four years. It was found that foals that developed DOD were larger at birth and grew more rapidly than foals without DOD.
If foals are fed for rapid weight gain, they will have an increase in bone mineral content, according to one study. However, the study showed that there were no differences in bone mineral quality in foals fed for rapid weight gain versus those fed for slow weight gain. Foals that do gain weight rapidly might have an increase in serum osteocalcin, indicating that more bone growth is taking place. However, an increased incidence of physitis in foals fed for rapid gain was observed.
Concerns over a connection between glucose intolerance and insulin resistance to development of osteochondritis dissecans (OCD) lesions prompted the development of an oral dextrose challenge test for glucose intolerance. Research at Rutgers found that there might indeed be an association of glucose intolerance and OCD.
Studies at Kentucky Equine Research on the effects of feed on the incidence of OCD indicated that providing feed with a low glycemic response could reduce the incidence of OCD.
Owners of young horses strive to make weaning time as stress-free as possible, and researchers wondered what the effects of weaning time are on body weight, wither height, and bone density. It was found that weaning had no effect; however, a decline in weight gain at one and three weeks after weaning is normal.
If young horses enter race training, there will be a period of bone demineralization, then a period of re-mineralization. A study of yearling Quarter Horses showed a significant decrease in the density of metacarpal bone believed to be caused by the exercise-induced bone remodeling. "The research indicated the onset of speed work often coincides with the time of greatest demineralization (50-60 days into training), which may account for the high incidence of skeletal injuries in 2-year-old horses in training," according to the authors of the study. "Training methods and protocols should be designed to reflect the findings that significant demineralization of metacarpal bone occurs in the first 60 days of training."
Further research shows that feeding higher levels of phosphorus, calcium, and magnesium than those recommended by the NRC might increase bone mineralization. And even for long yearlings not in training, calcium levels might need to be increased to 115% of NRC recommendations, according to Oklahoma researchers.
For many young horses, once training is begun, they are then confined to stalls. However, research suggests this might be detrimental. Michigan researchers found that confined long yearlings and 2-year-olds had a loss of bone mineral content in comparison with those on pasture. Rich recommended allowing young horses free access to exercise on pasture, or if this is not an option, then training should be modified to account for the bone loss. One product that might help prevent bone mineral loss is exogenous somatopropin (eST).
Rich said research in the past five years has provided the following tips for broodmare owners:
- Feed a mare a fat and fiber diet prior to weaning to help her handle weaning stress better than if she was on a carbohydrate-based diet.
- Mares kept in fat condition during fall and winter months are more hormonally prepared for breeding than thin mares. Fatter mares will continue to come into estrus, while thin mares will go into a deep anestrous state.
- Keep mares in a moderate to fleshy body condition before foaling to reduce the risk of poor pregnancy rates.
- Mares fed a fat and fiber concentrate will have healthier foals than those on a starch and sugar concentrate. They will also have increased linoleic acid in their milk, which might reduce the incidence of foal gastric ulcers and enhance passive immunity.
- In addition, certain digestive disorders might be reduced in mares fed a fat and fiber feed in place of grain.
- It is not necessary to feed more copper, zinc, and iron to pregnant and lactating mares than is recommended by the NRC. A study showed that overfeeding has no beneficial effect.
- If selenium supplementation is necessary, supplementing with 3 mg/day of selenium yeast is preferred over sodium selenite.
- To enhance colostrum and thus passive transfer, and to improve blood levels of vitamin E in mares and foals, supplement mares with 160 IU of oral dietary vitamin E/kg of body weight for four weeks before foaling and four weeks after foaling.
Performance Horse Nutrition
More tips were offered by Breuer on performance horse nutrition.
- Feed a high-fiber diet to endurance horses and other competition horses in prolonged exercise to help maintain fluid and electrolyte levels, resulting in fewer cardiovascular and thermoregulation problems.
- To achieve short-term hyperhydration, providing a hypertonic solution will help stimulate the horse to drink more water and will temporarily reduce the amount of urine output.
- Administering a hypertonic electrolyte supplement just before and during strenuous exercise will help the horse drink more, lose less weight, and maintain higher blood electrolyte levels.
- An isotonic electrolyte solution similar to equine sweat is preferred over an isotonic glucose-glycine solution for fluid loss and plasma electrolyte restoration in exercise-dehydrated horses.
- Glucose solutions appear to have no benefit when trying to maintain electrolyte and fluid balance.
- Feeding an 11.8% fat diet appears to adapt horses for greater fat utilization, which might enhance performance and allow less lactate accumulation in the body.
- Racehorses consuming predominately alfalfa diets might be at a higher risk for testing high for plasma TCO2 (an indicator of the total carbon dioxide content in the blood, which can indicate that illegal substances have been given to the horse).
- Diet composition or short-term feed restriction might affect the ability of horses to maintain blood glucose concentrations during exercise.
- Supplementing fat can help a horse's body use fat in place of glucose stores during exercise.
- Any potential benefits of feeding a horse grain within three hours of exercise are outweighed by a risk of hyperinsulinemia that might interfere with energy utilization in the performance horse.
- Grain should be withheld from horses before exercise, but small amounts of hay should be fed to ensure proper gastrointestinal tract function.
- Hay should not be reduced to less than 1% of body weight.
With more horses reaching geriatric status (over 20 years of age), it's important to understand how their nutritional needs change. Diets should be adjusted to help old-timers live a long and healthy life. David Pugh, DVM, MS, Dipl. ACT, Dipl. ACVN (nutrition), professor at Auburn University, presented "Feeding the Geriatric Horse" during the Current Concepts in Equine Nutrition session.
Pugh said that an older horse should have a complete physical exam, dental exam, and complete blood count and serum biochemistry panel to detect any problems. If an older horse has a medical problem, this information might affect the choice of diet.
If everything is normal, Pugh recommended that an older horse be given palatable, dust-free feedstuffs to minimize the risk of allergies and lung disease. These feedstuffs should be easy to chew and swallow to minimize the risk of choke. If an older horse is pastured with younger or more aggressive horses, Pugh said it is helpful to feed the older horse separately to insure that he gets to eat properly.
A healthy older horse should be fed enough energy for the amount of calories he is burning--crude protein at 12-16%--and high-quality fiber for normal gut function. It is important to make sure that the older horse is receiving enough vitamin C and vitamin B-complex and minerals to maintain nutritional health. He said vitamin C levels tend to be lower in geriatrics. One study showed that in older horses with depressed immune systems, giving 10 grams of vitamin C twice a day might increase antibody response. Since vitamin C is water-soluble, it is hard to detect toxicity; Pugh recommends not going above this level. He reminded horse owners to consult their veterinarians prior to feeding any supplement.
Pugh likes senior feeds as they have increased amounts of crude protein, fat, phosphorus, and vitamins; are easy to chew; and are palatable. Hay and grain should be of good quality. One to two cups of vegetable oil per day can be added to diets for additional fat. However, Pugh cautioned against adding fat too quickly; fat should be added slowly over a two- to three-week period.
When providing a feed other than a complete feed or commercial mix, digestibility should be taken into account.
If feeding hay cubes, up to a half-gallon of water per pound of feed must be added to decrease the chance of choke and colic and to increase intake. (See complete article #4026 online.)
About the Author
Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.
POLL: Feeding Alfalfa