Digestive Similarities and Differences to Horses
Both guinea pigs and horses consume large amounts of fibrous plant material. While their digestive systems differ (guinea pigs are coprophagic), both are hosts to beneficial bacteria in the gut that aid in the breakdown of these fibrous foods. Maintaining a healthy gastrointestinal tract is vital to the well being of these animals.
Our thanks to Tom Moates for permission to reprint his article on probiotics.
This article was first published March 2009 in The American Quarter Horse Journal, pp. 88-90.
By Tom Moates
The basics of probiotics and when you should consider them for your horse.
You toss a flake of hay over the fence. Your horse digs in, and the nutrition process begins as he chews. In his gut, bacteria break down fibrous material.
Can adding supplemental bacteria - known as probiotics - to your horse's diet improve his digestion even more?
Maybe. And that's where a dizzying array of probiotics products in the equine marketplace comes in. Each supplement sports a desirable sounding name and is presented as just what a horse needs to be healthy. So, how can you know if some health claims are true, or if a particular probiotic product is right for your horse? We asked some horse health experts for their advice.
The Good Guys
Just what are probiotics anyway? "Probiotics are dietary supplements containing potentially beneficial bacteria or yeasts," explains Dr. Judy Reynolds, Ph.D., P.A.S.
Reynolds is the equine product and technical manager for ADM Alliance Nutrition, Quincy, Illinois. She holds a Masters and doctoral degrees in animal science and nutrition, respectively from Texas A&M University and conducted her graduate research on bone strength in racing American Quarter Horses and feed considerations for horses with HYPP.
"The current Food and Agriculture Organization of the United Nations/World Health Organization definition is: 'Live microorganisms which when administered in adequate amounts confer a health benefit on the host,'" she said.
The organisms that fall under the heading of probiotics occur naturally in the environment, and are typically found in the gastrointestinal tract of host animals that consume plant material. In this situation, Dr. Reynolds explains, a symbiotic relationship is established between the host animal and the microscopic hitchhikers. Essentially, as rent for a cozy room in an animal's digestive system, they break down fibrous plant material into digestible compounds that otherwise could not be utilized by the host. This situation occurs in many animals, including humans.
In the horse, hundreds of beneficial organisms typically take up residence, mainly in the cecum and large colon. These enlarged areas of the gut provide a space for fermentation to take place. Fermentation is the process where cellulose and hemi-cellulose fibers, (which comprise a large percentage of hay, especially stems and stalks) are broken down by these organisms into a form that the horse can utilize. Only a handful of the most beneficial of these organisms are generally found in probiotic supplements.
The process of breaking down food begins when the horse chews it. This both mashes the material and mixes it with a considerable amount of digestive juices called saliva. Next, it is swallowed down into the stomach, and there mixed with more digestive compounds and worked around to continue the breakdown process. The digesta then passes into the small intestine. Many fats, proteins, vitamins, minerals, and soluble carbohydrates are readily absorbed through the lining of the gut in that area into the bloodstream to be sent for various uses in other parts of the horse's body. The horse is naturally equipped with the enzymes needed to break down much of the food without the help of other organisms.
The fibrous roughage diet of horses, however, also contains matter that is not digested by the horse's own natural abilities, and it passes as undigested food residue out of the small intestine and into the cecum. The resident beneficial bacteria in the cecum manufacture enzymes that can break down this otherwise unused material - mostly fibrous - through the fermentation process. The result is that these organisms benefit by feeding on the fibers and the horse is then able to absorb and use a great deal more of the remaining fermentation products that otherwise would pass through the digestive system as waste.
Reynolds also explained that the lining of the gut where these organisms are found is covered with finger-like surfaces called villi that increase absorption potential. Bacteria attach to these villi to live and grow. Reynolds said it is important to try to encourage beneficial bacteria to occupy these spaces that facilitate digestion, and displace less helpful bacteria
Probiotic-containing products available for horses in the marketplace today are designed to provide some of these beneficial organisms to the horse to ensure it is not lacking.
The brewers dried yeast that frequently is included in probiotic supplements has a somewhat different job to perform than the beneficial bacteria. This yeast is considered a healthy medium for beneficial bacteria to live in, but does not perform the duties of other microorganisms during fermentation. It is included to provide the service of promoting the health of the beneficial bacteria in the hindgut.
Probiotics are found packaged in a variety of ways. There are single-dose syringes like those that paste dewormer comes in, giving the product the feel of a medication. Bagged mineral or feed supplements can contain probiotics. Also, powdered, liquid, or granulated variations of probiotics exist that can be applied to feed.
When to Supplement Probiotics
"There hasn't been a tremendous amount of research on the horse with probiotics," said Tim Potter, Ph.D., P.A.S., the area specialized agent-equine with the North Carolina Cooperative Extension and North Carolina State University. He is also a longtime AQHA member.
Much of the scientific material on probiotics used to formulate equine products was conducted on other animals with similar digestive systems, like chickens. Ridiculous though that may sound to the horse owner, a basic understanding of what goes on in the gut in horses in relation to probiotics is widely accepted now from such research.
Potter pointed out that there is sound reasoning behind using probiotic supplements in certain circumstances in horses, with some evidence that probiotics can produce a positive effect.
As an example, Potter explains that when antibiotics are administered to a horse to treat an infection, bacteria are killed indiscriminately - both detrimental and beneficial bacteria are reduced in number. Providing a probiotic supplement at this time may help reintroduce beneficial bacteria to the horse's digestive system more quickly than would occur naturally, and thereby help to jump start more efficient digestion. He added, though, that some beneficial bacteria will remain in the gut, and will repopulate anyway. It is a question of accelerated recuperation times.
Horses under stress for any reason seem to be at greater risk for some or many of the existing beneficial organisms regularly occurring in their digestive systems to die off. It is thought increased acidity in the gut occurs during stress and kills the beneficial bacteria. In these horses, the scenario is similar to the above example, and the re-introduction of probiotics may hasten the re-colonizing of the digestive tract.
However, the stress itself must still be addressed. If conditions that are deadly to the beneficial bacteria persist, any new living bacteria consumed by the horse likely will be killed as well, and probiotic supplements ineffective at that time. Also, ingesting probiotics does not cure the high acidity in the gut caused by stress.
On another note, research indicates that well conditioned, happy horses living on pasture with a regular diet are unlikely to need any assistance keeping helpful resident bugs in the gut. Potter said that feeding a probiotic supplement at a recommended dosage should in no way harm a horse already with adequate populations; it simply would cause no noticeable benefit. Horses ultimately do not need the microbial extra helpers for survival, but they are necessary for maximizing the efficient use of forage.
Reynolds said there are reasons to add probiotics as a regular, daily supplement for horses in general. One is to constantly introduce beneficial bacteria into the digestive system to provide the maximum opportunity for them to acquire and hold the surface areas on the villi in the small intestine. Another is to provide yeast to the diet regularly, which is always a good medium for beneficial microorganisms in the hind gut.
Veterinarians tend to be in agreement with the Equine Nutrition Experts on the subject of probiotics. Tracy A. Turner, D.V.M., of Anoka Equine Veterinary Services, in Elk River, Minnesota, seems to sum it up perfectly: "I tend to use them (probiotic supplements) after a horse is super stressed, colicked, had diarrhea and their normal flora has been changed. It is one of those things we do in addition to other supportive care."