feeding growing horse

Protein, Energy, And The Growing Horse
NOTES FROM KENTUCKY EQUINE NUTRITION CONFERENCE ON EQUINE
GROWTH

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."
University Research
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.
Sensitivity Analysis
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.
Hot Button--Nutraceutical
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!

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