Horses in extreme conditions may need immune boosting to stay healthy.

Poor immune system function puts your horse at risk of serious infections, sometimes with unusual and difficult-to-treat organisms.

How Can You Tell?
Routine blood tests, such as a complete blood count (CBC) and blood chemistry, won’t always accurately predict how well a horse will respond to an infectious challenge, but there may be some clues that can help you determine if your horse’s immune system isn’t right where it belongs.

On the CBC, look for low total white blood cell (WBC) count, low lymphocyte count, elevated ratio of neutrophils (aka segs) to lymphocytes. There may also be anemia.

Those at highest risk are:
Foals Weanlings Seniors Cushing’s horses Stressed horses Horses turned out in weather extremes

On the blood chemistry, low levels of globulin may be found, or the enzyme GGTP may be high normal or elevated with other liver enzymes and liver function tests, like bilirubin, normal. GGTP can be elevated as an isolated finding when the immune system is trying to fight all its battles using primitive inflammatory responses.

If the horse is an adult, fecal exam may turn up evidence of parasites not normally found in healthy adults, such as roundworms and pinworms.

There are outward changes in the horse that can tip you off too, including:

Goopy eyes

Increased nasal discharge

Dry cough

Pot belly

Tail rubbing

Skin infections, itching, lice

Poor coat.

Be especially suspicious of poor immune-system functioning when the horse that develops these problems is the only one in the group to have them. It’s easy to dismiss isolated problems as “just overly sensitive to flies,” “has some allergies,” “needs a deworming,” etc. and overlook that they’re actually symptoms pointing to poor immune system functioning.

Beware Immune-Stimulant Herbs

A variety of herbs have been shown to be capable of stimulating one or more types of immune reaction. However, the arms of the immune system they stimulate aren’t necessarily the ones that are underactive in horses with weakened immune systems. In fact, it often is exactly the opposite. Immune-system-stimulant herbs given to otherwise healthy horses with normally functioning immune systems may help give a “wake-up call” or “red alert” that has their first-line defenses primed and ready for an infection, but this is rarely where the problem lies in horses with suppressed or weakened immune systems. Before considering these products, you need to consult with someone who is familiar with the specific immune system effects of the herbs.

Consider supplementing his hay with a protein-mineral supplement.

When immunity is weak, the horse’s body is more likely to respond with exaggerated inflammatory and allergic-type reactions than with the organism-specific antibodies and killer T cells he needs to actually get rid of challenges, including parasites. This in turn makes him more sensitive to environmental irritants too.

What can you do?
A thorough veterinary exam is in order to determine if there is an underlying medical problem that is weakening the horse’s immune response. If nothing is found, support consists of doing what you can to eliminate factors that stress his immune system, and providing the nutrients the immune system needs to function well:

If the horse is in work, back down on intensity and skip a few competitions.

Stable the horse during periods of extreme weather, such as heat or cold, and rain/snow.

Make sure a horse on group turnout is not being bullied.

Be sure the horse is not battling a parasite burden.

Consult your vet or a nutritionist to make sure your diet is balanced and meeting minimum trace mineral requirements, including selenium, and that both total protein and essential amino acid requirements are being met. Remember that both younger and older horses have increased protein needs.