Advances In Equine Nutrition: KER conference 1998
The nutrition conference for feed manufacturers presented by Kentucky Equine Research (KER) of Versailles, Ky., attracted more than 200 delegates involved in research and feed manufacturing from the United States, Europe, Australia, Brazil, Canada, and other countries around the world. Several world renowned speakers, plus graduate students from universities heavily involved in equine research, presented data from studies pertaining to nutrition and the well-being of horses. As in the past, the conference provided feed manufacturers and scientists a chance to exchange information concerning current concepts in feeding and managing performance horses. Some of the highlights of the meeting are outlined in this article.
Protein, Energy, And The Growing Horse
The first speaker was introduced by Joe Pagan, PhD, president of KER. Ed Ott, PhD, from the Animal Science Department at the University of Florida, spoke on energy, protein, and amino acid requirements for growth of young horses. Ott's presentation revolved around the concept that while vitamins and minerals must be balanced and are very important for growth in the young horse, energy and protein--and consequently amino acids--actually control growth rate. Growth rate can be accelerated or restricted by manipulating energy and protein levels in the growing horse's diet.
To further illustrate his point, Ott began a discussion of the specific energy and protein requirements of the young horse. Energy is derived from the metabolism of substrates such as carbohydrates, fats, and excess protein commonly found in equine diets. The efficiency of digestion of these substrates varies immensely.
Energy is required for all body functions. Ott explained that there are two ways to determine the energy requirements of young horses--by conducting a feeding trial or by using the factorial approach. He further explained that the factorial method involves the determination of the energy needs of an animal for maintenance, then adding the energy required for growth. The National Research Council (NRC, 1989), which sets guidelines for nutrient requirements of horses at various life stages, found from the data in literature that the daily digestible energy (DE) requirement for maintenance of mature horse was DE (Mcal) = 1.4 + .03 Bwkg (body weight).
As an example, a foal weighing 300 kg has a DE requirement of DE (Mcal) = 1.4 + .03(300) = 10.4 Mcal/day. To determine how much additional energy is required for tissue energy deposition, the equation DE (Mcal) = (4.81 + 1.17X - 0.023X2) (ADG) where X = age in months and ADG is average daily gain in kg, is used. Combining the two equations gives the equation for daily digestible energy requirement for the growing horse: DE (Mcal) = (1.4 + 0.03 Bwkg) + (4.81 + 1.17X - 0.023X2)(ADGkg).
From the results of his own research, Ott felt that this equation actually over-estimates the requirement for weanling horses, but underestimates the requirement for yearlings.
The protein requirements of the growing horse are determined by the relationship among the amino acid requirements of the foal, the amino acid content of the feed ingredients, and the digestibility of those amino acids. The amount of protein required in the diet is related to how well the amino acid composition of the feed matches the amino acid requirements of the foal. Ott explained that since both energy and protein restriction will reduce growth of the animal, a constant relationship, or ratio, exists between energy and protein needs. The following equations express this relationship: Crude Protein (CP, g/d) for weanlings = 50 g per Mcal DE, CP (g/d) for yearlings = 45 g per Mcal DE. This relationship works only if the amino acid composition of the protein used in the diet is of good quality for horses and therefore meets or exceeds the amino acid requirement of the individual.
Following the discussion of protein requirements, Ott provided information about specific amino acid requirements. Most of the data concerning amino acid requirements of young horses revolve around feeding trials that compare growth rates of youngsters on diets with varying concentrations of amino acids. Lysine has been determined to be the first limiting amino acid, with methionine, tryptophan, and threonine vying for the position of the second limiting amino acid (most data indicate threonine as the second limiting amino acid, especially for young horses on all-grass diets). Diets that are low in limiting amino acids can be enhanced by the addition of soybean meal, which has an amino acid profile complementary to the needs of the growing horse.
"The objective of any feeding program is to maintain a moderate, steady growth curve," says Ott. The growth rate of the foal at any point is the function of the animal's age, genetic potential for growth, and nutrients available to the animal at that time. In reality, most foals do not grow consistently, but energy and protein should be managed to try to achieve steady growth. Weaning is a particularly erratic time for growth in young horses, and often weanlings will only maintain themselves or actually lose weight.
Ott implied that the key to minimizing the variability in the animals is to provide an optimal quantity of nutrients for each phase of the growth cycle. Generally, this requires that the animal be maintained on a concentrate balanced to be fed with a specific forage program. The NRC recommends that energy intake of the growing foal be met by feeding a concentrate to forage ratio of about 70:30 for weanlings and 60:40 for yearlings. Ott indicated that data from his laboratory suggest that weanlings averaged a ratio of 62:38 and yearlings averaged 64:36.
Since horses of this age will consume about 2.4 to 2.6 lb/100 pounds of body weight of feed per day, a 600-pound weanling will consume 9.0 to 9.6 pounds of concentrate (60-64%) and 5.4 to 6.0 pounds of hay (36-40%) daily. Based on Ott's results, these numbers are in agreement with the general opinion that horses should consume no less than 1.0% of their body weight per day of forage for proper digestive function.
Other data from Ott's lab indicate that the NRC might have under-estimated energy requirements for weanlings while over-
estimating the requirement for yearlings. He said that the differences could be within the expected variation that exists between animals and feeding programs, or that the requirements actually might need to be adjusted.
As an alternative to increasing the amount of grain fed to the growing horse, the addition of 5% fat to the concentrate will increase the energy density by about 10%. This allows the concentrate portion of the diet to be reduced, which could be beneficial for the growing horse. High concentrate diets have been implicated as a source of bone development problems in growing horses due to the effects of insulin in response to large grain meals.
As a final suggestion for feeding young horses for moderate, steady growth, Ott mentioned that protein requirements can be met by using a lower overall protein level in the concentrate, then adding 0.2% lysine to the ration. For example, if the overall ration were 15% CP, a 12% concentrate with 0.2% added lysine could be substituted. This might prove to be more economical while still providing the proper amounts of amino acids required by the growing horse. He pointed out that it is important to provide the vitamin and mineral concentrations that would be included in the 15% protein level feed because the foals still will grow at the same rate as expected from the higher protein product.
In conclusion, Ott stated the following: "At typical intake ratio between 70:30 and 60:40 concentrate to forage, energy protein and amino acid concentrations will provide appropriate nutrient intakes to support optimal growth in most weanlings and yearlings. When specified lysine concentrations can be provided using lower protein concentrations, similar growth responses can be expected. If the energy content of the concentrate is increased by the addition of fat, it is probably appropriate to increase the protein and/or lysine concentrations to compensate for the lower feed intake.
Nutrient Requirements Of The Growing, Exercising Horse
Brian Nielsen, PhD, from Michigan State University, spoke on the topic of nutrient requirements of the young, exercising horse. Nielsen noted that many horses enter a training program as yearlings or early 2-year-olds. That individual has to be fed to meet requirements of growth as well as exercise. Little research has been conducted on the working, growing horse, and there are several explanations as to why. First, the process of training young horses is very labor intensive. It is very difficult to put an adequate number of horses in training for a controlled study. Second, researchers usually are forced to use animals which have not been competitive in the discipline for which they were bred, which might produce results that are not representative of that group. Third, the experiment cannot be repeated with the same horse because the horse continues to age. For those reasons, the researcher often is better off using adult horses in training and combining conclusions from those studies with results of research conducted with young horses.
Despite the difficulty in obtaining good experimental animals, a lot of informative research has been performed over the years. Feeding fat to performance horses as an alternative source of dietary energy has been of great interest to many scientists. Numerous studies have shown that fat added to the horse's diet can increase the energy density of the diet without greatly increasing intake, while at the same time allowing for a reduction in the amount of carbohydrate being fed. Studies have shown that up to 20% of the total diet can be fed as fat without negative effects on palatability of the diet or performance (Duren et al., 1987). Feeding fat might be beneficial in meeting the increased energy requirement of the growing, exercising horse. Nielsen was quick to point out, however, that as exercise increases, so does the demand for energy. Therefore, the question remains as to whether the requirement of other nutrients also is increasing. In other words, if fat levels are increased, it probably will be necessary to increase the other nutrients to keep the nutrient:calorie ratio the same.
If an abundance of energy is provided, but other nutrients are available only in limited amounts, growth will continue, but it will be of poor quality. Nielsen suggested the use of concentrate feeds that have been balanced with fat included instead of top-dressing fat onto an otherwise balanced ration. By top-dressing an already prepared ration, the total nutrient balance becomes diluted, and it becomes necessary to rebalance the diet.
Horses can adapt to high levels of fat in the diet rather quickly. Thoroughbred horses in training were able to adapt to fat supplementation within one week and showed increasing muscle glycogen stores within 21 days of receiving fat-added diets (Hughes et al., 1995). Increasing muscle stores indicates that fat might provide a glycogen-sparing effect when fed as a source of energy. This effect would allow fats to be used preferentially instead of glycogen, says Nielsen. If fats are used for non-anaerobic activity, more glycogen is likely to be available to the horse when it begins to work anaerobically.
Nielsen also discussed protein requirements for the young, exercising horse. Many people believe horses in training have a high requirement for protein, but that is not necessarily true, he says. One study (Frank et al., 1987) found no benefits or detrimental effects of feeding either a 10% or 20% protein ration to 2-year-olds in training. Often, feeds containing higher protein levels are more expensive, and most people assume higher priced products are of better quality.
Feeding excess protein is expensive, and in order for the horse to get rid of the extra nitrogen resulting from the breakdown of protein, urine production increases to compensate for the extra ammonia produced. The result is a wetter stall, more ammonia, and higher risk of respiratory irritation. In general, the total protein requirement of the young horse entering training is only slightly increased from maintenance. Most nutritionists agree that if a DE:CP ratio is maintained, increased consumption will provide enough additional protein to meet the needs of the young exercising horse (Freeman et al., 1988; Hinkle et al., 1981).
Mineral balance is another area of great concern for the growing, working horse. Calcium retention increases with exercise in the young horse, and Nielsen suggested dietary amounts of calcium should be increased as young horses enter training. The NRC recommends 0.32% calcium in the total diet for long yearlings in training, and 0.31% calcium for 2-year-olds. However, following a series of experiments that indicated a potential deficiency in calcium in young horses as they entered training, Nielsen believes a more suitable concentration could be closer to 0.40% calcium in the total diet.
While research has indicated some changes in dietary mineral levels are needed for the growing, exercising horse, the same cannot be said of vitamin levels. Nielsen noted one exception: thiamine. Thiamine is a B vitamin needed for the metabolism of dietary energy and pyruvate. If the absorption of thiamine (produced in the hindgut by microbes) is not adequate, there can be a dietary requirement (Carroll et al., 1949). Horses which are possibly deficient in thiamine can become "track sour." These animals are generally depressed, go off feed, and become lethargic. Trainers should be aware of these symptoms, especially in very hard-working horses consuming large amounts of grain on a daily basis.
Gastric Ulcers In Performance Horses
Steve Duren, PhD, who handles nutrition consultations for KER on the West Coast, presented information concerning management of ulcers in performance horses. The incidence of gastric ulcers in performance horses is extremely high, with as many as 80% of racehorses affected. Most of the lesions occur in the upper half of the stomach, which is lined with squamous epithelial cells similar to the tissue found in the esophagus. This tissue does not have a mucosal layer, and bicarbonate, which acts as a buffer, is not secreted onto its luminal surface. Therefore, this region is highly susceptible to ulceration.
"Ulcers in this region are very similar to 'heartburn' in humans," said Duren.
It has been determined that gastric ulcers in horses are not caused by the bacteria Helicobactor pylori, which are a common cause of ulcers in humans.
In the region of the stomach where ulcers occur, the only protection from acid comes from saliva, which act as a buffer. The horse's stomach secretes acid continuously. Because the horse is naturally a free-ranging, grazing herbivore, it would normally spend the majority of the day browsing and consuming fibrous plants. In this setting, the stomach acids produced are constantly buffered by a steady flow of saliva. But stabled horses do not feed in this manner. They are managed by schedules that are convenient to their caregivers, and for that reason, often are fed large, infrequent meals. That type of feeding program often exposes the horse to long periods of fasting, leading to excess gastric acid output and less-than-adequate saliva production for buffering.
Different approaches can be taken in treating ulcers. Several classes of drugs are used that inhibit gastric acid secretion. These include Histamine-type-2 antagonists, H+/K+ATPase inhibitors, and Prostaglandin analogues. An alternative to these drugs would be to neutralize the stomach acid. Duren suggested the use of an "antacid" manufactured by KER called, appropriately, "Neigh-lox."
Originally, KER tried to develop an antacid for horses using preparations similar to those used in human antacids. One ingredient commonly used in humans, magnesium oxide, caused some horses to become ataxic and display signs of tying-up. Another class of antacids contains aluminum, which is the active ingredient in Neigh-lox. When fed, Neigh-Lox will neutralize acid production for about six hours. Results from field trial use have been very positive in relieving symptoms associated with gastric ulcers, reported Duren.
"Neigh-Lox' more important role, however, may be in preventing ulcers from occurring in the first place," says Pagan. "Antacid therapy, in addition to a feeding program that utilizes forage on a continual basis, may greatly reduce the incidence of gastric ulcers in performance horses and foals."
In recent years, the KER conference has included poster presentations of recently completed research conducted by students at the University of Kentucky. This year, graduate students from several universities,--including the University of Kentucky, University of Florida, Virginia Polytechnic Institute and State University, Blacksburg, and Michigan State University-- had the opportunity to present posters. Some of the highlights of the poster presentations included the following:
The effect of level and type of dietary fiber on hydration status following dehydration with furosemide--L. K. Warren et al., University of Kentucky. This study focused on using soluble fiber sources to help retain water in the hind gut for use during long-term exercise. It was found that horses consuming forage high in soluble fiber (such as alfalfa) drank more water, had greater fecal moisture, and had lower plasma total protein after being dehydrated with furosemide. Also, horses eating diets high in soluble fiber had more body water prior to dehydration with furosemide. These results suggest a diet high in soluble fiber might provide the horse with a source of dispensable water in the hind gut during dehydration.
Influence of chromium picolinate on growth and energy metabolism in horses--University of Florida. In this study, chromimum picolinate was added to the diets of Quarter Horse yearlings at various concentrations. Diet did not affect weight, withers height, heart girth, body length, or hip height. Glucose was metabolized more rapidly by animals receiving the highest concentrations of chromium picolinate as evidenced by a more rapid decline in plasma glucose following glucose injection. Chromium did not appear to have any effect on insulin sensitivity.
Stalling young horses alters normal bone growth--K. E Hoekstra et al., Michigan State University. This study compared the effects of placing young horses in stalls for long periods prior to the onset of training. Yearlings were divided into two groups. One group was housed in box stalls and the second group was kept on pasture. Radiographs showed that stalled horses had decreased bone mineral content. It appeared that housing yearlings in stalls might negatively affect normal bone growth experienced by yearlings allowed to remain on pasture. Free access to exercise might provide enough loading on the bone in the legs to promote normal growth.
David Kronfeld, BVSc, from the School of Veterinary Medicine at Virginia Polytechnic Institute and University, gave a thought-provoking, and at times philosophical, lecture concerning rations and formulation of diets for horses using a "range" of nutritional values instead of one, specific value. Kronfeld said, "The traditional approach to designing a diet or supplement leads to a single solution--for example, one concentrate formula for each forage analysis--to achieve nutritional goals expressed as requirements (NRC, 1989). In contrast, the procedure called sensitivity analysis specifies nutritional goals as target ranges and tests the effect of the ranges of nutrients in ingredients and proportions of concentrate:forage consumed. It acknowledges and deals with variations that exist in animals and feedstuffs, and for pasture-fed animals, the huge errors in estimating pasture intake."
His reasoning behind this school of thought is that because a great deal of variation exists between animals and the feedstuffs they consume, "sensitivity analysis" gives a more accurate estimate of intake using upper, lower, and middle values.
"Practical nutrition needs to have optimum ranges, whereas nutritional science determines only minimum requirements," says Kronfeld. This type of analysis could be very important for horses on pasture where intake is hard to determine.
The word "nutraceutical" has been popping up in literature concerning health topics with increasing frequency. This year at the KER conference, Kathleen Crandell, PhD, the East Coast nutritionist for KER, explored this multi-billion-dollar business. People are flocking to health care stores and purchasing nutraceuticals for themselves and their horses because there is a perceived notion that these products are "natural" and, therefore, very safe. Unfortunately, this is not always the case. To compound the problem, defining exactly what a nutraceutical is at this point is difficult because of poor regulation of the industry. Some of the questions Crandell tried to resolve for the audience were as follows: What is the legal definition of a nutraceutical? How do nutraceuticals differ from a nutrient or a drug? What rules govern their safety and efficacy? What nutraceuticals have found their way into the horse industry?
A nutraceutical is commonly defined by the dietary supplement industry as "any non-toxic food component that has scientifically proven health benefits, including disease treatment and prevention." The veterinary community has its own definition, which includes the following: "A substance which is produced in a purified or extracted form and administered orally to patients to provide agents required for normal body structure and function and administered with the intent of improving the health and well-being of animals."
Nutraceuticals are not feeds because they do not have nutritive values, and they are not drugs because they have not gone through any drug testing processes. The rules governing human nutraceutical uses were set forth by the Dietary Supplement Health and Education Act (DSHEA) in 1994. The DSHEA rules do not apply to nutraceuticals intended for use in animals. Because of this, claims of a product's effects other than what would normally be ascribed to "food" could cause that product to be regulated as an unapproved drug. As far as safety and efficacy are concerned, no specific guidelines have been set. In many instances, for many products available today, little or no testing has been done. Krandall suggested that a simple test of the quality of a nutraceutical product would be to ask for research data (peer reviewed and published) that support the product.
In the horse, the role of nutraceuticals can be easily defined--diminish disease signs or improve performance. Much of the data used to promote nutraceuticals for equine use have come from human studies. Krandell warned that results from human studies were not always applicable to use in horses. Some of the nutraceuticals that have been studied for use in horses are carnitine, Coenzyme Q10, Creatine, DMG, HMB, MSM, and oral joint supplements.
Manufacturing Horse Feeds
The final portion of the conference was devoted to issues concerning feed manufacturing, and included speaker Keith Behnke, PhD, from the Department of Grain Science at Kansas State University. Behnke opened his talk by saying that genetic improvements are creating better-quality animals, and therefore, the feed manufacturer has to constantly improve the quality of the product being produced to feed these animals. Some of the areas of concern for the manufacturer are as follows:
1) Grain particle size and its effect on animal performance;
2) Feed (nutrient) uniformity and its effect on animal performance;
3) Pellet quality issues.
Particle size and grinding of the grains in feed have been the subject of many research studies. Grain that has been ground prior to mixing has been shown to improve feed efficiency in pigs. Behnke talked about the actual type of mill used in the processing--hammermills vs. roller mills, and how pigs fed with corn that had been ground in the roller mill actually had higher digestibility of dry matter, nitrogen, and gross energy than the pigs fed corn ground in a hammermill. While Behnke didn't actually cite studies conducted with horses and the effects of grinding on feed efficiency, it is known that fermentation rate is increased as particle size is reduced in ruminants. At this point, there is not much information available concerning the effects of fine grinding on hind gut fermentation in horses.
Equally important as grinding feed to improve feed efficiency is mixing the feed so that the finished product is uniform. Improper mixing of feed can result in reduced diet uniformity, which can lead to poor animal performance. It also becomes a problem for the manufacturer because the resulting product might not comply with feed manufacturing regulations. Behnke suggested that feed manufacturers develop a mixer testing procedure that is acceptable to both the industry and regulatory agencies. Currently, a "standard" is not in place regarding accuracy, safety, and expense of mixing feed.
Pelleted feeds always are the source of debate among horse people. Some owners and managers love feeding pelleted products, while others think whole grains in sweet feeds are the best way to feed horses. While the argument rages on, several aspects of pelleting feeds are clear. Feeding a pelleted ration 1) Decreases feed wastage; 2) Reduces sorting of ingredients; 3) Pelleting procedures destroys pathogens in feed ingredients; 4) Less time and energy are spent eating; 5) Starch and protein are modified by heat, which makes them more available to the animal; and 6) Palatability often is increased.
The inability of the horse to "sort" out the part of the palatable feed and to leave the less-palatable portion is probably the best advantage of using pelleted feeds. Perhaps the most important issue concerning pellet use for horses is quality. Owners often place a high value on packaging and presentation of a product and expect the product to be clean, bright, and smell good. Behnke stressed the point that manufacturers should pay close attention to all of these details when designing pelleted products for horses.
Future trends in the feed manufacturing business include hygienic treatment of feeds to provide clean, pathogen-free products; pellet moisture and quality control using coolers and driers; and the inclusion of liquid vitamin, mineral, and enzyme ingredients to improve the availability of the nutrient to the animal.
Bob Coleman, PhD, from the University of Kentucky, concluded the second session with a summary of information concerning the role of processed grain in feeds for horses. According to Coleman, the question of whether grain should be fed to horses whole or processed (rolled, crimped, steamed) has been an issue for horse handlers for more than a century. Interestingly, horse owners believe grain is better digested when processed because hulls are observable in the manure of horses fed whole grains. Coleman suggested that there is undigested matter in the manure of horses fed processed grains, but it is less easily identified.
Studies that have been conducted with horses concerning feed processing have shown the following:
1) Processing oats has little effect on nutrient availability;
2) Steam flaking/rolling barley did improve daily gain in yearlings;
3) Grinding/heat processing corn increases the availability of the starch fraction of the grain;
4) Feeds for young horses under one year of age should be processed--pelleted being the best product for creep feeds.
In conclusion, Coleman said, "The cost of processing grain must be evaluated in relation to the improvements in performance." He suggested that everyone should stop worrying about the hulls in the manure because they are there even with rolled or crimped products, just harder to see!
About the Author
Amy Gill, PhD, is an equine nutritionist that specializes in growth, metabolic, and exercise-related disorders of the horse. She is a contributing writer to many popular press magazines, provides consultation, and recently developed Equi-Force Equine Products LLC. Her Web site is www.amymgillphd.com.