When one talks about a specific horse feed or a feeding program, some
horse owners routinely ask, "What is the protein content?" It
is the opinion of some horse owners, breeders, and trainers that protein
is a magical feed ingredient. Protein is often the only nutrient that
some horse owners consider, which may explain why some feeding programs
fail. Without a doubt, protein is both greatly overemphasized and
misunderstood by many horse owners. For the sake of simplicity and
space, the term "horse owner" will also include breeders and
trainers in this discussion. Why does this misunderstanding exist about
protein?
- First, there appears to be a lack of basic nutritional knowledge
among some horse owners.
- Second, some feed companies have used and promoted the sale
of their products on the basis of protein content.
- Third, the fact that the percentage of protein must be
stated on the feed label may also lead owners to believe that it is
more important than other nutrients.
In contrast, the energy content is not listed on most feed labels.
All these situations can contribute to misunderstanding the role of
protein in horse nutrition and aids in explaining this distorted picture
regarding protein.
Horse owners should first select feeds on an energy or caloric basis.
Energy is a nutritional need, not a nutrient. The 1989 National Research
Council (NRC) Nutrient Requirements of Horses calculates the protein
requirements on the basis of a horse's energy needs. Too often a horse
owner may think that protein alone will make foals grow larger, mares
breed earlier and produce champion foals, and performance horses win
more often. Horse owners should be aware that protein is only one of six
classes of essential nutrients. Other than water, no class of nutrients
is more or less important than the others. Horse owners should also be
familiar with the basic functions of protein in the body, critical
functions but not of greater significance than the functions of
carbohydrates, fats, minerals, or vitamins.
Amino Acids
Proteins are made up of amino acid chains, which can be complex or
simple. Of the 22 amino acids, ten are considered essential and must be
provided in the diet. Non-essential amino acids do not have to be
supplied via the diet. Nonessential amino acids can be synthesized by
microorganisms in the horse's cecum and anterior portion of the large
colon and by metabolic processes in the body. Just how effectively amino
acids produced in the horse's lower gut are utilized is not presently
known.
Protein Functions
Protein serves a multitude of roles in the body. Protein is used to
build and repair body tissues. Basically, all body tissues and organs
contain protein in rather significant amounts. Some of protein's best
known uses are as major components of muscle, enzymes, and hormones.
But, protein is also a critical component of bone, skin, hair, internal
organs, and hooves. Consequently, protein is an important structural
component of the body and also aids in regulating many of the bodies'
systems and functions. Protein makes-up about 80% of a horse's body
composition on a waterless, fat-free basis. While protein is vital for
the proper daily functioning of the body, this does not make it
"superior" to other nutrients.
Protein Requirements
All horses require protein, but the amount and quality of protein needed
vary considerably among the different life stages of horses (growth,
pregnancy, etc.). Protein requirements are listed in Table 1 on page 2.
It comes as no surprise that a young, growing horse has a greater
protein need compared to a mature, pleasure horse, due to its rapid
muscle and skeletal growth as a suckling, a weanling, and a yearling. On
the opposite end of the protein requirement spectrum is the
non-reproducing, non-lactating, non-performing mature horse (known as a
maintenance horse), which requires the least amount of protein. Some
horse owners feed 1% to 2% more protein than recommended by NRC. While
this is an unnecessary and costly practice with mature, maintenance
horses, it is not usually detrimental. There are indications that some
foals are capable of growing more rapidly than noted by NRC. These foals
would require more protein and energy than suggested by NRC
recommendations.
Protein Quality
It is not enough that a horse's diet contains an adequate amount of
protein, but the type of protein also becomes very important in young,
growing horses. Protein quality refers to the amount and ratios of
essential amino acids. Research has shown the first limiting amino acid
in young, growing horses, or the most likely amino acid to be lacking in
the ration, is lysine. Adding lysine to poor-quality rations fed to
young, growing horses results in higher daily weight gain and more
efficient gain. The NRC established lysine requirements for weanlings
and yearlings are 2.1 and 1.9 grams per Mcal of DE daily, respectively.
Recent research has shown that threonine may be the second limiting
amino acid for young, growing horses. Presently, there are no
established requirements for threonine.
It is critical that protein quality be considered when formulating all
rations for young, growing horses. Some feeds that tend to be high in
lysine are milk by-products, soybean meal, canola meal, sunflower meal,
and alfalfa hay. It is important to understand that protein quality is
less important with mature horses. The major concern with adult horses
is protein quantity rather than protein quality.
Protein-to-Calorie Ratio
The relationship of protein to energy (calories) is important,
especially when feeding young horses. Some of the problems associated
with creep feeding sucklings, as well as feeding weanlings and yearlings
may stem from an improper protein-tocalorie ratio . The NRC states
rations for weanlings should have a proteinto- calorie ratio of 50 grams
of crude protein per megacalorie of digestible energy.
When rations with a lower protein-to-calorie ratio (lower than NRC
recommendation) were fed, weanlings ate less feed, grew slower both in
daily gain and wither height, and had less body condition. Such a ration
can occur when there is inadequate protein compared to the ration's
energy content. But, reduced growth can also happen when too much
protein exists in a ration compared to its amount of energy. This
situation often occurs when horse owners add too much supplemental
protein to a commercial feed formulated for young horses.
Based upon research, it may be advisable to feed a protein-to-calorie
ratio of 50-55 grams of crude protein per megacalorie of digestible
energy for sucklings and weanlings.
The protein-to-calorie ratio recommended by NRC for mares in late
pregnancy is 44 grams of crude protein per megacalorie of digestible
energy. For lactation, the recommended ratio is 43-50 grams of crude
protein per megacalorie of digestible energy. Mature horses at
maintenance need 40 grams of crude protein per megacalorie of digestible
energy.
Too Much Protein
As noted previously, some horse owners feed too much protein. A major
concern with this practice is an improper protein-to-calorie ratio,
especially with young, growing horses. This problem can occur when an
18% protein concentrate high in oats is fed along with a grass hay. Both
oats and grass hay are low, or relatively low, energy feeds.
Extra protein, above the body's requirement, can be utilized as energy,
if needed. When not used for body functions, parts of the protein
molecules are stored as body fat. Cost is a factor when excessive
protein is fed. The cost of protein is too high to be used as an
economical energy source. Grains (such as oats, corn, and barley) and
vegetable oils (fats) are more efficient sources of energy.
Excess protein results in nitrogen being converted to ammonia, then to
urea by the liver. As a result, blood urea nitrogen content increases
and the extra urea is excreted in the urine. Water intake increases,
which results in greater urine volume and a noticeable ammonia smell,
especially in poorly ventilated stables. If a strong ammonia smell
exists in a barn, it could indicate that too much protein is being fed.
Wetter stalls and ammonia odor add to management problems by increasing
bedding and labor needs and costs. Ammonia, close to the stall floor,
can be a problem with young foals, including predisposing the foal to
pneumonia. Too much protein also can be a problem in older horses which
have kidney or liver disease.
Too Little Protein
Since protein is needed for many body
functions and growth, a deficiency of protein can result in serious
problems. A common sign of protein deficiency is lower feed intake.
Horses eat less of a protein deficient ration, not more as one might
expect. A number of other factors can also cause a drop in feed intake.
Reduced growth would be evident in foals fed a protein deficient ration.
A slower growth rate results in less daily gain and wither height
growth, as well as less body fat. These conditions have also been
observed when the ration's protein content was apparently adequate, but
the protein-to-calorie ratio was less than 50 grams of crude protein per
megacalorie of digestible energy.
Other commonly observed signs of protein deficiency are a rough haircoat,
reduced hoof growth, and abnormal skeletal development in young, growing
foals. In lactating broodmares, milk production will be reduced, which
results in slower foal growth.
Protein Sources
Most common grains fed to
horses contain 6% to 12% protein, while hays may contain anywhere from
4% to 20% protein. Legume hays, such as alfalfa and lespedeza, contain
more protein than grass hays. Grass hays usually contain 6% to 10%
protein while legume hays provide 11% to 20%. Normally, grass hay and
grainbased concentrate feeds are adequate in protein content for mature
horses. But, such rations do not usually contain enough protein for
young, growing horses and mares in late pregnancy or early lactation.
When extra protein is needed, a protein supplement can be added to the
ration. Protein supplements are usually plant meals, made from soybean,
cottonseed, or linseed (flax). Recently, protein supplement feeds have
been made from canola, sunflower, and safflower. Normally, soybean meal
is used as a protein supplement because of its availability, price, and
protein quality, especially for young, growing horses, and broodmares in
late pregnancy and lactation. In the past, linseed meal was touted for
horses, but its lower-quality protein and cost make it less desirable
today.
In the southern states, cottonseed meal may be fed more
frequently due to its availability. It has a slightly higher digestible
protein level with a better balance of amino acids than linseed meal. In
the past, some cottonseed varieties and processing methods resulted in
high gossypol content of cottonseed meal. Gossypol is a chemical toxic
to horses. Current processing methods and low gossypol varieties of
cotton have reduced this risk. However, before using large amounts of
cottonseed meal in horse rations, horse owners should ensure toxic
levels of gossypol are not present.
Weanling foals have been
successfully fed 0.2% free-gossypol cottonseed meal. Young, growing
horses do not gain as rapidly or as efficiently when fed cottonseed meal
as compared to soybean meal, due to cottonseed meal's deficiency of
lysine. A higher level of cottonseed meal must be fed or the cottonseed
meal must be supplemented with lysine when fed to young, growing horses.
A number of by-product protein sources, such as corn gluten meal or
feed, corn distillers' grain, and brewer's dried grains, are also used
in horse feeds. Generally, these sources are of lower quality protein
and should preferably be used with high-quality protein sources,
especially if used in rations for young, growing horses.
Because of
their high lysine content, milk by-products are often used in rations
for young, growing horses and may be used for other horses, such as
pregnant or lactating mares.
Performance
Horses and Protein
Horse owners and trainers often feed more protein to performance horses
compared to amounts fed to mature, maintenance horses. This practice is
not necessary. While there is an increased protein need for performance,
considering the nitrogen loss in sweat and exhaling, this increase is
not great. The major nutritional concern with performance horses is an
increased energy need. Consequently, performance horses are usually fed
more concentrate (grain) feeds. Since more concentrate is fed, the
performance horse actually has a greater intake of protein, which
readily satisfies its need for more protein.
It is not necessary to increase the protein percent of a concentrate
feed to 14%-16% for mature, performance horses. A 10% protein feed is
adequate when fed with a good-quality grass hay, since the amount of
grain fed is increased to meet the energy need. The extra grain fed
provides the small amount of additional protein needed due to increased
performance.
Too much protein in the diet can reduce performance. Feeding 1-2% extra
protein is probably not detrimental to most performance horses. However,
feeding excessive protein (3-5% or more) may have deleterious effects on
metabolic parameters of protein breakdown. One example is increased
urinary nitrogen excretion which may result in higher ammonia levels in
air that could negatively affect respiratory health.
Broodmares
and Protein
The NRC considers the first eight months of pregnancy as a maintenance
requirement with a protein need of 7.2%. The protein requirement
increases in the 9th, 10th, and 11th months of pregnancy (see Table 1 on
page 2). Protein needs during these months increase more than that of
energy (22% in the 9th month, 24% in the 10th month, and 32% in the 11th
month over maintenance). However, research indicates the first 40 days
of gestation may be a critical time for the pregnant mare. During this
time period, early embryonic death has been shown to be high when mares
were on poor-quality feeding programs. Protein quality (especially
lysine requirements) may be more important in early lactating mares
which are being bred than previously thought.
Non-lactating broodmares are often placed on a higher plane of nutrition
30 to 45 days before being bred. Such a program includes adding grain to
the ration to increase energy and protein intake. It seems advisable to
continue such a feeding program until broodmares are pronounced in foal
at 40 days of pregnancy. It has been shown that broodmares can be
conditioned to store body fat for energy use during late pregnancy and
in early lactation. In contrast, horses cannot store any appreciable
amount of protein in their bodies. As noted previously, protein fed
above the body's requirement is converted into energy and/or stored as
body fat and/or excreted. Consequently, feeding an adequate amount of
protein in late pregnancy and early lactation is very important, since
mares do not have body stores of protein to draw upon.
Young,
Growing Horses and Protein
 Young,
growing horses have the highest protein requirement on a percentage
basis (see Table1) Protein quality is also critical with young, growing
horses, which require specific amounts of the dietary amino acid lysine.
High-quality protein promotes not only proper weight gain, but also
skeletal and muscular growth in weanlings. New research has shown that a
lower protein ration (9%) supplemented with adequate lysine (0.6%) and
threonine (0.4%) resulted in equal or greater growth in young, growing
horses from birth to yearling age compared to feeding a higher protein
ration (14%). This proves the importance of protein quality in diets for
young horses. It is possible that future research will show other amino
acids to be limiting in the rations of young, growing horses.
Feeding high-quality protein feeds, such as milk by-products, soybean
meal, and alfalfa hay, should ensure an adequate intake of amino acids
as currently needed for young, growing horses. Some foals gaining more
rapidly than noted by NRC may require additional protein and lysine to
support faster growth. For this reason, some owners feed 2% to 3% more
protein to sucklings, weanlings, and yearlings than NRC recommends.
Summary
Protein is one of six nutrients needed by horses. Protein is needed for
many body functions. Requirements for protein vary depending on the life
stage of the horse, with younger horses having a greater requirement
(percentage of the ration). Protein quality is more important for young,
growing horses. Excesses and deficiencies of protein can create
problems, especially when an improper protein-to-calorie ratio exists.
Protein should not be viewed as a mystical nutrient. Horse owners need
to keep in mind that a higher protein percentage in the ration, beyond
the horse's requirement, will not enable the horse to achieve a greater
level of performance.
|
