Not Your Usual Suspects, Part 1 - When Water is Toxic
For my next two blogs, I’d like to share some situations in large animal veterinary medicine when toxicities are found where you’d least expect — in the ordinarily life-sustaining compounds, water and oxygen. Let’s begin with water.
There is such a thing as water toxicity. When I first learned this in vet school, I was both horrified and fascinated. Turns out, this really is a case of something being too much of a good thing. When water toxicity occurs, which thankfully isn’t too often, it usually occurs in pigs. Here’s what happens.
Pigs raised indoors, as most pigs in the U.S. are raised, are dependent on the pig farmer for food and water. Many watering systems in large hog operations are mechanically operated with large piping systems that carry water from a central tank or well to pens containing multiple pigs. Occasionally, something goes awry with the watering system, like a power outage, broken pipe, or a situation where someone forgets to turn the system on after service, and the pigs are without water. This is when disaster can strike.
As the pigs become dehydrated, their electrolytes become unbalanced. Within 24 to 48 hours, the neurologic system begins to be affected. Pigs will act uncoordinated and appear blind, then demonstrate a behavior called head pressing. These clinical signs are not specific to dehydration. Meningitis, inner ear infections, and some exotic (and therefore reportable to the state veterinarian) swine diseases can also appear this way. However, with water toxicity, all hogs in a pen or barn will have the same signs.
This usually isn’t the case with an infectious disease, where different animals will show different signs depending on the stage or progression of the disease and the animal’s immune system. This is how a vet or farmer can start to differentiate between a mechanical problem in the barn versus a serious disease outbreak. Whenever hogs demonstrate neurological signs such as these, a good hog farmer will first check the watering system.
Dehydration such as this, medically known as salt toxicity, is as easily cured as one might think: Just give the pigs water! However — and this is a big however — the key is to introduce the water slowly. If severely dehydrated hogs are given ad libitum water all of a sudden, water toxicity develops. The brain swells quickly and neurologic symptoms will continue and are likely to kill the pig.
So what’s a farmer to do? It is often recommended to take a water hose and sprinkle the hogs with it so that small shallow puddles collect on the ground. The hogs can then lap up very small quantities of water over a period of a few hours, and then the process is repeated, ensuring a gradual return back to hydration.
If hogs are neurologically affected to the point of being unable to drink for themselves, then the farmer has his work cut out for himself. Syringe feeding water to a group of hogs may be necessary. The administration of intravenous fluids is not practical in hogs; the location of their jugular veins makes catheterization very difficult.
You may be thinking to yourself: Isn’t prevention worth more than the cure and shouldn’t the farmer simply ensure the water doesn’t get turned off?
In practice, on large hog farms, water is frequently turned on and off for numerous reasons. In some cases, medication for hogs is administered via drinking water and logistically determining which pens receive medicated water and which don’t involves frequent water shut-offs. Additionally, sometimes farms simply run a well dry — a scary issue during drought, for sure.
Next Wednesday, we’ll take a look at another toxic element, oxygen, and how veterinarians use it to help cure infection.
Dr. Anna O'Brien