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David W. Horohov Ph.D., Maxwell Gluck Equine Research Center, University of Kentucky

I love the “wow” factor in associations and reminded myself of that experience when I reviewed the tape I made of Dr. David Horohov at the 2010 Mid-Atlantic Nutrition Conference.

Horohov reminded us of the complexities of disease and the circumstances of fact-finding. He gave a talk on rhodococcus equi, a nasty foal disease, but he wove in stories of HIV, the hygiene theory, and the wire walk of how to jump-start one system while leaving another alone.

Rhodococcus equi (RE) is a disease that plagues foals, usually under 2 months, and is known for its distinctive diarrhea and its production of pneumonia. It has veterinary, time, labor and worry costs associated with it and it can kill. Just like the human population, diarrhea and dehydration go hand in hand and little bodies dehydrate pretty quickly; and if the runs don’t get them the lungs drowning in fluid might. Pneumonia is always serious.

The little bugger that causes this disease is ubiquitous. It is everywhere in the ground. Yup, you too are stepping on RE somewhere on your farm. It’s just like ants, if you don’t have them, chances are nothing around you is breathing, including you.

Some farms are plagued more than others and for years the general direction has been cleanliness is akin to healthiness.

Taking a look at RE the first thing that jumps out is that this everywhere-in-the-air disease doesn’t much affect adults. In fact, it is pretty unusual to have an adult with RE.  Turns out the adult horse population has immunity to this little bugger. So the thinking was that the younger horse population had no immunity. And so the thought went until the medical community identified rhodococcus equi in AIDS patients. Huh? The medical community thought the same thing so they started looking into this. (told you the bug was ubiquitous) Human medicine has funding and the results found in that sector were scooped up by the equine medical community.

It was discovered that the foals had immunity, but the immunity just wasn’t kicking in yet. Their bodies had to be “sensitized” to the bacteria, rather like the act of a vaccine. To take a sentence from Horohov’s extract “While most cellular components of the immune system are present at birth, in many cases these cells can be considered immature or lacking full functional capability.”

How do you get an immune system to “grow-up”? One theory (I always want to make sure that people realize we are talking about the discovery phrase, not the we-know-it-for-sure phase.) is that the immature immune cells grow-up to be productive members of the organism by being challenge. This gives some strong meaning to the aphorism, “What doesn’t kill us makes us stronger.”

How do you sensitize a foal? They actually “challenged” their immune system by bringing them into a less than pristine barn for four hours everyday (with mom). This is a scary thing to say because I always worry how others interpret the statement. The foals were getting good management, nutrition, and the barn didn’t have 3 feet of manure in the stalls with no ventilation. It was just dirty, maybe not all the manure and urine out of the stalls, maybe not all the dirt swept from the aisles.

The findings were that these foals didn’t get the disease at the same rates their pasture counter parts did. A lot more work needs to go into this, a lot more blood pulled, conditions researched, etc. But it took the first step in saying maybe these foals need a little challenge in their life. (Horohov discussed the pivotal immunity thruster, interferon gamma, and how it kicks in, but you need lots of cups of coffee to deal with that story.)

It also makes sense in light of the “hygiene” theory.  Human studies that show kids who aren’t exposed to animals, flora and fauna early on in life are much more susceptible to developing allergies later. I see this in the Icelandic horse population where a horse imported from pristine Iceland has a 30% chance of developing summer eczema (allergy) when it hits the states; yet, the domestic-bred Icelandics don’t show this propensity.

If further research confirms these initial findings and theories, the equine community can look into how to beef up immunity faster. It is there, just start the engine earlier. Is there an intra-nasal spray that can be used, a vaccine, a probiotic to feed? But in interfering with a foal’s immunity system can you end up damaging the immunity that mom has passed on? Questions that won’t be answered for a while. But the first step is taken- knowing a bit more about the little bugger and the system it attacks.

Meanwhile, I am starting to see the value in the adage “ you need to eat a pound of dirt before you’re 12.” There just might be something to that.

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