Polioencephalomalacia is a nutritionally related disorder, commonly referred to simply as "polio." It is an infrequent but frustrating malady that usually begins occurring about this time of year. There are a couple of other diseases that can appear similar, but are caused by infectious agents.
Although not discussed in textbooks, consulting veterinarians tell me there is a condition known as the nervous form of coccidiosis. There is also apparently another similar malady that to my knowledge has never been identified.
This mystery disease occurs (sporadically) in backgrounding yards during periods of extreme cold. Calves suddenly go down and die in a manner similar to polio (described later), but on necropsy by the veterinarian, it's not found to be polio.
Signs Of Polio Veterinary pathologists can readily identify classic nutritional polioencephalomalacia by examining brain tissue. Veterinarians I have worked with tell me that this mystery disease I have described leaves no identifiable pathology. Most have surmised it is caused by a virus ... but that is not known with any certainty. True polioencephalomalacia, on the other hand, has a known cause. True polio is caused by an induced thiamin or vitamin B1 deficiency.
As a general rule, ruminants can synthesize their own B vitamins. More correctly, rumen microorganisms synthesize B vitamins and the host animal absorbs them for their own use. In polioencephalomalacia, vitamin B1 or thiamin is still synthesized by rumen microorganisms, but for some reason an enzyme that destroys thiamin is also produced. This enzyme is produced in quantities so massive that they overwhelm normal thiamin production, which causes the animal to become paralyzed.
The actual paralysis is quite characteristic. The animal (usually a 400- to 600-lb. calf) goes down, with the head and neck stretched back, and legs stiff and straight. Death usually doesn't occur for a couple of hours or more, and if treated promptly, recovery can be complete. Treatment consists of intravenous injection of thiamin and glucose. Most feedlot veterinarians will routinely instruct feedlot "doctors" in how to treat polio, and likewise thiamin and glucose will be kept on hand.
There has been relatively little research with polio, primarily because we don't know how to induce it. In other words, we don't know what causes it (what triggers the production of the thiamin-destroying enzyme). All we know is that it seems to occur primarily in the fall; typically with calves being brought up on high concentrate rations.
Feeding Thiamin Not Necessary I've heard of recommendations to feed large amounts of thiamin as a preventative. However, I am not aware of any research supporting that idea. I have also been aware of attempts to administer large amount of thiamin as a therapeutic means to overcome polio, but to my knowledge they have been failures. The amount of thiamin enzyme produced is so great that it has destroyed virtually every amount that has been administered (orally). Thiamin must be injected (intravenous) to bypass the enzyme in the rumen.
Several years ago I began doing work for a backgrounding yard that was adding large amounts of thiamin to their ration. I convinced the owner to delete the thiamin. To date, only nominal instances of polio have occurred. Had we left thiamin in the ration, obviously we would think it was working.
Certainly, there is nothing wrong with putting thiamin in the ration, other than the expense. Even if it did work, however, polio is so sporadic I'm not sure it would be economical. I'd rather put the money into top-quality cowboys. If caught (and treated in time), calves will recover. We know that works.
One of my clients used to say, "It doesn't cost but a couple of hundred dollars a month more to get a really good man ... and he'll easily save you that much in reduced equipment damage." In this case, a little extra money to hire conscientious cowboys can save several times as much in unnecessary (and probably ineffective) thiamin.