Allergies,
heaves, thrush, insect bite reactions, and hives all can reflect a
struggling immune system, as can the more obvious signs of
respiratory disease.
Some
infections and diseases are beyond your control, but you can
influence the outcome by boosting your horse's immune response
nutritionally.
Stress
and the Immune System
One
of the best things you can do for your horse is pay attention to his
stress level and adjust activities accordingly.
Chronic stress,
whether physical or mental, weakens his immune system. When cortisol,
the stress hormone, becomes elevated, disease agents that don't
normally faze your horse might make him sick--for example, equine
herpesvirus (EHV).
Did you know that your horse might already be
infected? This opportunistic organism can remain latent until
something (e.g., stress) triggers it, giving it the "opportunity"
to cause clinical signs.
Encountering
some stressors is inevitable: Horses travel long distances,
congregate in strange settings with unfamiliar horses, and are
subject to performance stress and other factors. But one of the most
common stressors--an empty stomach--is easy to fix. Horses are
"trickle feeders" that evolved to roam and graze freely.
Not being permitted to graze at will works against a horse's
physiology. This is because the horse's stomach, unlike our own,
secretes acid continuously, even when empty. Chewing produces saliva,
a natural antacid, but it can't help neutralize stomach acid if the
horse is left with nothing to chew. Exercising on an empty stomach
causes acid to slosh onto the unprotected areas of the stomach's
lining, potentially causing ulcers.
Nutrients
to Protect Your Horse
Healthy,
well-managed pastures supply your horse with many important
nutrients, including vitamins E, A (as beta carotene), and C.
Grasses
are also high in omega-3 fatty acids in the proper proportion to
omega-6s.
And if a variety of grasses and clover grow in your
pasture, you can expect the protein quality to be good.
While
free access to pasture often provides all the nutrients a horse at
maintenance requires to remain healthy, many horses rely on hay as
their main forage source during winter.
Hay loses some of its
vitamins and omega-3s in storage, so horses consuming only hay for
prolonged periods of time (more than three or four months without
fresh pasture) might require additional feed supplementation.
Most
horses do well on a fortified commercial feed in recommended amounts.
But if your horse exhibits signs of suppressed immune function (e.g.,
signs of respiratory infections including a runny nose, coughing, and
fever; recurrent thrush; bacterial infections; fever; allergic
reactions; and general malaise), it's time to boost his diet's
nutrient content.
Your
horse might need the following vitamins and minerals to fill
nutritional gaps and maintain a healthy immune system:
Vitamin
E is
a powerful antioxidant. Antioxidants protect against disease by
neutralizing the damaging free radicals (unstable molecules with an
unpaired electron that pull electrons from other molecules) that
mental and physical stress produce.
Rhode
Island's Department of Fisheries, Animal and Veterinary Sciences, and
colleagues examined the impact of vitamin E dosages 15 times the
National Research Council's recommended levels on aging horses'
immune systems. They found that horses supplemented with vitamin E
were more capable of fighting bacteria and produced increased amounts
of the antibody immunoglobulin. However, Carey Williams, PhD,
associate extension specialist and associate professor at Rutgers
University's Department of Animal Science, discovered that just 10
times the recommended dose of vitamin E in otherwise healthy horses
interfered with Vitamin A absorption. Gross excess supplementation is
not recommended, therefore, even in chronically stressed horses.
"The
benefits of vitamin E as an antioxidant and its ability to improve
immune function have been known for years--vitamin E impacts several
key components of immune function," says Stacy Oke, DVM, MSc,
president of Rolling Thunder Scientific, in Ontario, Canada. "There
are four different types of vitamin E: α, β, γ, and ? tocopherols.
What remains to be known is which types are the most effective."
Many
different tocopherols exist in forages and other sources. The form
manufacturers most commonly add to commercial feeds and supplements
is α- tocopherol. When added in its natural state manufacturers note
it as d-α tocopherol in the ingredients, and in its synthetic
version they list it as dl-α tocopheryl acetate. Natural vitamin E
is more effective as an immune system booster than the manufactured
vitamin; however, the synthetic form is more stable and, therefore,
has a longer shelf-life.
Vitamin
E works parallel to selenium compounds that also serve as
antioxidants. University of Kentucky researchers found that a low
blood selenium status experienced a delayed immune response to
vaccinations. However, selenium can be toxic in high amounts, so
horses should only be supplemented if veterinarians document a
deficit, and supplement levels should be kept low (below 5 mg/day for
an average-sized horse). Vitamin E and selenium are commonly packaged
together; evaluate the diet's total selenium content before adding
more. For therapeutic doses, it might be better to purchase vitamin E
alone.
Vitamin
A, in humans, is necessary for normal regeneration of mucosal
barriers damaged by infection, and it enhances the function of
neutrophils, macrophages, and natural killer cells--three types of
white blood cells critical to the immune system. Plants contain beta
carotene, which the body uses to produce vitamin A. Beta carotene,
vitamin E, and vitamin C work synergistically to reduce inflammation
and protect lipids in cell membranes against free radicals' damaging
effects.
Boon
Chew, PhD, of Washington State University's Department of Animal
Science, explains that beta carotene has been reported to modulate
the immune system in humans and animals. It increases the ability of
specialized white blood cells to damage harmful cells. The resulting
inflammation helps eradicate bacterial and viral pathogens and
stimulates production of various cytokines, which are messenger cells
in the immune system. Beta carotene also stimulates blood
neutrophils' phagocytic ability, by which they engulf and eliminate
bacteria.
Since
most vitamin/mineral supplements and feeds are fortified with vitamin
A, it is important to monitor levels before supplementing. The active
form of vitamin A (Retinol, retinyl compounds) is toxic at five times
the National Research Council's recommended level.
Vitamin
C neutralizes free radicals through its ability to donate
electrons. The horse's liver normally synthesizes vitamin C in more
than adequate amounts and releases and excretes it during periods of
prolonged stress. Sarah L. Ralston, VMD, PhD, Dipl. ACVN, associate
professor in Rutgers' Department of Animal Science, theorizes that
older horses' increased susceptibility to infections might be due to
the chronically elevated cortisol secretion associated with pituitary
dysfunction (equine Cushing's disease). Ralston finds vitamin C to be
an effective supplement in reducing the effects of stressful travel.
"We verified that after prolonged transportation stress, oral
supplementation (with) vitamin C twice a day was beneficial for the
horses the first few days after arrival," she explains.
Omega-3
fatty acids have been shown to reduce inflammation as well as
allergic inflammatory response in other species. Researchers at the
University of Guelph's Equine Research Centre found evidence that the
fatty acid source flaxseed can potentially reduce the allergic
inflammatory response in horses susceptible to biting midges
(Culicoides). Omega-6 fatty acids can exacerbate inflammatory
responses if fed in large amounts, but omega-3s do just the
opposite--they help inflammation subside. Omega-6 fatty acids are the
predominant form in edible oils such as corn and soybean that are
commonly used as calorie supplements. If given in reasonable amounts
(less than 2 cups per day to an average-sized horse), they should not
pose a threat to a horse's inflammatory system. Some omega-6 activity
is beneficial, since inflammation is another way the body combats
infections.
High-Quality
Protein
At
least 8% of a horse's diet should be high-quality total crude
protein. A high-quality protein has all the essential amino acids in
their proper proportion to allow for adequate body protein synthesis.
This enables the immune system to produce antibodies and enzymes and
to repair tissues. High-quality protein sources for horses include
legumes such as alfalfa, clover, and soybeans. For horses fed
lower-quality grass hays, add legume hay pellets or cubes to provide
high-quality protein. If you feed a commercial product, check for
alfalfa or soybean meal on its list of ingredients.
Other
Supporting Nutrients
Some
veterinarians and manufacturers have said the following supplements
further boost immune support, though these claims haven't been
scientifically proven:
Bioflavonoids
These supposedly work with vitamin C to enhance antioxidant
capability.
Coenzyme
Q10 Used primarily in humans, nutritionists are just starting to
recognize this substance as a potent player on the antioxidant team.
Water
soluble vitamins Thiamine, niacin, panthotenic acid, B-6,
riboflavin, and cyanocobalamin work together to support digestion,
skin, hooves, hair, blood vessels, protein synthesis, nervous system
health, and energy production in all species, and their use and
excretion is enhanced during periods of stress. However, in horses
only thiamine has been clinically proven to be necessary during
periods of prolonged stress. Scientists have not documented deficits
of the others in horses.
Spirulina
Blue/green algae reportedly reduces allergy signs and improves
respiratory function in other animals
Reference
http://www.thehorse.com/articles/30983/feeding-for-immunity
