Probiotics definitely have their place in equine medicine. However, we’re still a long way from really understanding that place and having a good grip on effective probiotic use in horses. In my experience, probiotics too often are overused, inappropriately used, and even inappropriately formulated for horses. We still know too little about the veritable universe of micro-organisms which normally inhabit the healthy horse’s digestive tract to know what, if any, microbes we should be adding, and in what quantity and for how long. Only a handful of studies on probiotics have been conducted in horses so far, and in some of those studies specific micro-organisms thought to be beneficial as probiotics actually caused diarrhea and other digestive upsets.
There are other issues with probiotic products, not the least of which are quality control (whether what is listed on the label is actually in the product, the viability of the organisms, etc.) and dosage (how many organisms are needed, and for how long). But that’s a topic for another time.
The most intriguing probiotic product I’ve come across so far is Primal Defense by Garden of Life. It’s a human product formulated to supply the types of micro-organisms we’d naturally get from the soil via our food if we lived a more natural lifestyle and ate a more natural diet. I love this product for dogs and cats (and humans), but for horses I recommend it only for chronic, unresponsive digestive disturbances or following intensive antibiotic therapy. Provided the horse gets to graze for at least a few hours per day, he should be getting a good quantity of these beneficial soil organisms directly from nature, so probiotic supplements should not be needed.
Absorbent properties of clay
Microbes aside, some horses appear to eat dirt primarily for its absorbent properties. Clays, in particular, contain very absorbent particles which can bind up bacterial toxins, organic acids, certain viruses, and other potentially harmful molecules in the gut. The bound toxins are then harmlessly removed from the body in the manure.
I have known seriously ill horses with disordered digestive tracts to selectively eat the clods of dirt that cling to the roots of a clump of grass rather than eating the grass itself. That’s not to say that if a horse is eating dirt then she may be seriously ill. However, it is worth considering that she may have a digestive upset of some sort. For example, there may be too much starch or sugar in the diet (whether from grain or lush grass) which has disordered the normal microbial population of the digestive tract. In addition to restoring the microbial population in the bowel, eating dirt may be helping simply by virtue of its absorbent properties.
There are several different clays that have been refined for use as medications or for the prevention of digestive problems in feedlot cattle on high-grain diets. They include kaolin, bentonite, montmorillonite, and smectite. I used to use bentonite as a feed additive in uptight horses on high-grain diets. It worked very well to calm the horse and normalize the manure, which otherwise was loose and smelly. (These days I much prefer to decrease the amount grain in the diet and use fat instead to meet the horse’s caloric needs.)
For horses with digestive problems, and for those who continue to eat dirt despite salt and mineral supplementation and plenty of pasture turnout, it may be worth reviewing the diet and, if dietary changes don’t do the trick, adding BioSponge (
www.platinumcare.com) to the diet for awhile. BioSponge, as the name suggests, is a dietary aid that contains one of the super-absorbent clays. It has been tested in horses, in an independent study at the University of California-Davis, and found to effectively absorb bacterial toxins in the horse’s bowel. While the horse may get what she needs by eating dirt, I’d prefer to use a refined clay rather than dirt, with all its impurities and who-knows-what-else.
Other reasons
For horses who eat dirt out of boredom or habit, providing more grazing time (or more simulated grazing time in the form of hay), more company, and more daily activity which is physically and mentally stimulating should help. If the horse is eating dirt because of a disease which is affecting mental function, then there will likely be other behavioral or physical indicators of illness. These horses require veterinary attention.
Why do horses chew wood and debark trees?
Wood eating can be normal behavior in horses, or it can indicate a problem, such as illness, inadequate dietary fiber, or boredom. Bark, branches, roots, and other seemingly inedible plant parts form a small but important component of the horse’s natural diet. These plant parts provide extra fiber and a diversity of nutrients. Bark, twig, and root eating may also be a form of self medication in some instances, as these plant parts often contain substances with medicinal properties (e.g. anti-inflammatory salicylates in white willow bark). But that’s a topic for another time.
As they rely on it for digestive health and energy production, horses have an absolute need for dietary fiber (“roughage”). The rock-bottom minimum amount of roughage needed per day is 1% of the horse’s body weight, calculated on a dry matter basis (i.e. taking into account the water content of the food). Well-made and properly stored hay is less than 10% water, so to keep the mathematics simple, let’s say it is close enough to 100% dry matter. That means the daily minimum fiber requirement, if the horse consumes little or no pasture, is 10 lbs of hay per day for a 1000-lb horse (1% of 1000 is 10). That’s just to meet the horse’s minimum fiber requirements; calories, protein, vitamins, and minerals will very likely be lacking at this level. Most horses are much healthier and happier when fed good quality roughage at a rate of 1.5% to 3% of body weight per day (15–30 lbs of hay, if pasture is limited).
Depending on the time of year, the water content of pasture grasses can be over 70% (i.e. less than 30% dry matter, including dietary fiber). In the spring and sometimes in the autumn, when the grass is lush and rapidly growing, a horse on full pasture turnout may not be able to meet his minimum daily requirement for dietary fiber from pasture alone, even when there is plenty of grass. At these times, horses on pasture often benefit from supplemental hay to meet their daily fiber needs.
If the horse is not getting his fiber requirements from his diet, then he will go in search of it. That’s when horses begin chewing fence posts, boards, wood stall doors or partitions, trees, etc. Bored horses also have a tendency to chew these objects. So, in addition to providing more variety in the diet and more pasture turnout (and/or hay), also provide more physical, mental, and social stimulation for the horse.
Why do horses eat manure?
Manure eating (coprophagia) can be normal behavior in horses. In young foals, eating the mother’s manure is a normal developmental stage. Through this behavior the foal learns to explore his environment and use his senses to make choices about what is palatable and what is not. He is also getting some dietary fiber and the beneficial intestinal microbes needed to support his own digestive processes once he begins eating solid food. In addition, the healthy intestinal microbes are an effective barrier to pathogenic bacteria which could adversely affect the foal’s health.
In older foals and adult horses, manure eating may be a way of supplementing intestinal microbes, dietary fiber, and perhaps other nutrients that are lacking in the horse’s own diet. Coprophagia is normal and nutritionally necessary behavior in rabbits, a species whose intestinal tract is very similar to that of the horse. Many nutrients released or produced by microbial breakdown of dietary fiber, as well as the microbes themselves (which are a rich source of proteins, lipids, vitamins, and numerous co-factors), are lost in the manure. Rabbits make effective use of these valuable nutrients by ingesting manure for a second pass. Perhaps some horses who eat manure are doing a similar thing, particularly if they are on a very restricted diet (e.g. dry lotted with just poor quality grass hay because they need to lose weight).
Manure eating in horses can also be caused by boredom or social disorder (e.g. isolation, incompatible company, frequent changes in the horse’s turnout routine or companions). As with dirt and wood eating, taking a closer look at the horse’s diet and management should identify where improvements may be needed.
Copyright ©2006 Christine King BVSc, MACVSc, MVetClinStud
Copyright © 2007 The NW Horse Source, LLC