Opisthotonos, polyneuritis, beriberi, polioencephalomalacia, bracken and nardoo. What do these words all have in common? Thiamine.
Thiamine? Is thiamine deficiency a problem in ruminants? Not usually. Despite some enthusiastic claims to the contrary, sheep and cattle usually get enough thiamine from their digestive tracts. In the rumen, some microbes routinely manufacture thiamine for their own private metabolisms. This is very convenient for our livestock because after each bug dies, its thiamine can then be absorbed across the digestive tract and used by the host animal. It's convenient, simple and effective.
Except when something goes awry … then we see a problem – classically a downer animal showing neural symptoms which dramatically respond to thiamine injections. Veterinarians usually call this disease "polioencephalomalacia," which is a very fancy term for thiamine deficiency in ruminants. We need to note here that polioencephalomalacia has nothing to do with human polio, which is an infectious viral disease controlled by vaccinations. Unfortunately, polioencephalomalacia in animals is also sometimes called polio, but the animal syndrome is a nutritional deficiency, not an infectious disease.
So why discuss thiamine now? Because the growing season will begin next spring, and there are a couple of plants we should know about.
Some chemistry first: Thiamine is a funny-looking molecule, kind of like an unbalanced dumbbell, with two dissimilar rings at each end linked together by a short chain of carbon atoms. Sometimes, things come along that split this chain – like certain types of sulfur compounds, which are often found in molasses. Also, an entire family of enzymes called “thiaminases” make their living by cleaving that carbon linkage and destroying thiamine molecules. Unfortunately for our livestock, some plants specialize in producing thiaminase enzymes. If our sheep and cattle eat enough of these plants ... goodbye thiamine, hello polioencephalomalacia.
Two of these plants are fairly common: horsetail and bracken fern. Most of you have seen horsetail (Equisetum arvense), a short, non-flowering, hollow-stemmed plant that resembles a horse’s tail (at least it did to someone). If you rub it between your fingers, you’ll find that it’s surprisingly rough to the touch – it has a high silica content. In fact, I used to use it instead of steel wool to scrub pots during camping trips. It often grows on wet ground and is rather unpalatable to livestock. Horsetail contains all sorts of toxins, including thiaminase.
Bracken fern (Pteridium aquilinum) is even more common – it’s the classic fern plant in meadows and open woodlands across North America. It often grows in very thick stands. People sometimes collect the young bracken shoots, called “fiddleheads,” as a gourmet delicacy, which is unfortunate because these shoots contain carcinogenic (cancer-causing) compounds.
Livestock don’t usually eat horsetail or bracken because those plants are not very palatable.
But in the early spring, these plants often come up quite heavily at a time when other green feed is short – and some animals, especially exploratory lambs and calves, may munch them in spite of our wishes. Also, during the summer these plants may end up in the hay, particularly in heavily infested fields. I’ve seen worrisome stands of these plants here in many fields. The hay-drying process apparently does not inactivate the thiaminases. Therefore, if large amounts of bracken fern or horsetail are in the pasture or hay (particularly bales that come from certain areas of a field) at 20% or higher, the hay may contain enough thiaminase to cause a problem. Horses are particularly susceptible to thiamine problems if they consume this type of hay for an extended period of time (enough time to deplete enough thiamine from enough cells).
Thiamine deficiency can also show up in other scenarios – high-grain diets, certain feed additives, high sulfur levels and of course the “I don’t have a clue” situation that occurs when you least expect it. Basically, there’s a lot we don’t know about the production and destruction of thiamine in sheep and cattle.
However, a lot is known about thiamine in human nutrition. Thiamine is the vitamin we all learned about in high school – you know, the cause of beriberi in humans and polyneuritis in chickens. You may remember your lessons about the first discovery of vitamins – about Dr. Christiaan Eijkman observing beriberi in people fed polished rice in Jakarta (then called “Batavia”) in Indonesia during the late 1800s. Eijkman conducted his experiments with chickens, and when he fed them brown rice or rice polishings, the problem went away. Thus, thiamine was the first B vitamin discovered, hence the name “vitamin B1.” (It’s a good thing we didn’t discover 235 B vitamins – that naming system would have become a bit cumbersome.) But thiamine’s discovery did not mean that beriberi disappeared quickly. A lot of education had to take place first. In fact, as late as 1947 in the Philippines, thiamine deficiency was the second-leading cause of death after tuberculosis.
Which brings us, of course, to "nardoo."
This is a strange and unlucky story: Nardoo (Marsilea drummondii) is an Australian fern that grows near streams. In 1861, two explorers, Robert Burke and William Wills, undertook an epic journey across some of the most distant regions of the Australian outback. They trekked from central Australia up to the northern edge at the Gulf of Carpenteria and then back again. But as they neared their base camp during the return trip, they ran out of provisions and, tragically, could not locate the supply caches left for them by their support team. Starving, they subsisted on the only green plants in the area, nardoo, which at that time of year grew abundantly along the banks of Cooper Creek. Unfortunately, nardoo contains quite a bit of thiaminase – at levels 100 times greater than bracken fern. For thousands of years, the local aborigines had successfully used this plant for food, but they made it safe by first soaking it in water before eating it. The aborigines tried to give advice, but the hungry explorers insisted on using a different method to prepare the nardoo, and they continued to eat their fill of it. Their appetites remained good until the end, but they lost energy, could not travel quickly enough to find help and eventually died, probably of thiamine deficiency.
And finally, there’s "opisthotonos." What a word! Try this word out on your veterinarian – she may be so impressed that perhaps she’ll give you a discount on your next invoice. In any case, opisthotonos means stargazing. Not the romantic kind of teenage viewing of the heavens from the front seat of their car, but the frightening, muscle-clamped, strained position of an animal with its head thrown back over its shoulder. It’s almost too painful to look at. Opisthotonos is a common symptom of thiamine deficiency in livestock.
But don’t automatically assume the animal has polioencephalomalacia. Many other problems can cause this dramatic symptom, including listeriosis, lead poisoning and rabies. So, if you see opisthotonos, handle the animal carefully ... and check the ration.
