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.
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:
Increased nasal discharge
Skin infections, itching, lice
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.
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.