Tag Archives: immune system

  • What? Is It Time For My Horses's Shots Again, Already?

    Written By Walt Friedrich

    Well, maybe, but let me pose a few questions first:

    Other than for Tetanus, when was the last time you had a vaccination?

    Do you consider your immune system to be reasonably strong?

    When you’re in the midst of a crowd, do you ever feel unsafe because there may be people nearby who have a contagious disease?

    Now, ask yourself the same questions with respect to your horse.

    Interesting, isn’t it? If you’re like most folks, you haven’t been vaccinated since you were a child (except maybe for Tetanus, if you cut yourself in the barn recently). And yet, you’re not worried about being near sick people in a crowd. If you give it some thought, would you come to the conclusion that you’re still protected from those illnesses because of all those childhood injections you endured, and your immune system is strong? It’s a logical explanation – we know contagious diseases can spread easily (evidenced, for example, by shocking conditions in some third-world countries), yet you – and most everyone you know – are spared. Well, feel good about it. You should. In large part, it’s because of those childhood injections – even though they took place many years ago!

    S0 now consider the contrast between your situation and your horse’s: if you’re like most horsepeople, your horse is younger than you are – and yet your horse may have received “shots” regularly, perhaps every year, while you received them only ONCE, long ago. His kind has been around at least as long as ours, and, like us, he’s survived pretty well – and, also like you and me, without benefit of all those injections during most of those millennia, thanks to our good, strong immune systems! See the dichotomy?

    The typical domestic horse is the subject of repeat inoculations every year or two, and always against the same threats! How strange. As history has amply demonstrated, his immune system is quite adequate, and for all but the current miniscule percentage of his species’ total history he received no injected protection, but now he’s apparently considered to have such a weak immune system that it needs frequent reinforcement inoculation.

    The pharmaceutical companies that formulate the injectibles tell you, virtually in unison, that it is simply not safe to take your horse to a horse show and risk exposing him to other horses, or that there is imminent danger that a bug may bite your horse and infect him with some horrible virus, and therefore your horse should be vaccinated again...never mind that he was just boostered last year. Yet you, without a booster, are at the same horse show, even though you are just as much at risk as is your horse. Why are you not pressured to receive the same injectable precaution?

    Which leads to the obvious question: could it be that yearly vaccinations for our horses are unnecessary? Over the years your horse has very likely been vaccinated for the same diseases repeatedly, and to some of them he has developed immunity. Yet powerful stuff is pumped into his system with every booster shot -- could the practice of over-vaccinating our horses actually be causing him harm?

    No-one is claiming that horses should never be vaccinated, but rather that over-vaccination is a problem. Make note, however, that some changes have actually been made in some parts of the world: there is often a longer time interval between tetanus vaccinations than there is with most vaccines, for example. Perhaps we should be traveling farther down this path.

    Let us pause for a moment and consider that much that you have just read might be called the contrarian viewpoint. It’s logical, we need to give it that, but it’s also pretty strong. But now let’s have a look at the other side of the story.

    A newborn foal is very well-armed as he enters life, provided he receives his mother’s colostrum as he suckles. His natural protection is quite limited, but the colostrum contains his mother’s full repertoire of antibodies. A great way to start life, better even than your and my childhood vaccinations.

    When he’s six months old, or thereabouts, his inherited immunity has declined somewhat, but he has also begun to develop his own immune system inventory of protection, adding to what’s still there from his mother. He should now bolster his colostrum-provided protection  by getting his first array of shots -- the equine version of our childhood inoculations.

    So far so good, he’s ready to face the world. But it’s the adult world, now, and he faces adult horse situations. Since the purpose of vaccinating is to stimulate the immune system to create protective antibodies, his new arsenal will protect him from future attacks. But some of these menacing microbes are great at evasion – they mutate, with the result that the stock of antibodies in the bloodstream and cell walls may not work on an attack by a mutation, and he can suddenly be in trouble. Further, the lifetimes of different antibodies are not all equal, some quite short, in fact. Consider the common cold in you and me – one cold is never enough, it seems, because we continue to “catch” them throughout our own lives. Either the antibodies we’ve built up are short-lived, or maybe what we “catch” is a mutation that’s changed enough that our antibodies may not recognize it. The same considerations apply to our horse. Pharmaceutical companies that develop the injectibles need to be constantly alert for new strains, and must develop new vaccines to counter them. It is a long-term, continuous effort, a sort-of early-warning system, to track tomorrow’s potential invaders.

    Of course the vaccine manufacturers are in business for profit, and if their products do not do the job, then veterinarians will not use them and horse owners will not buy them.  If a vaccine does not do its job well, it will not last long on the market.  On the other hand, manufacturers must act conservatively and make realistic evaluations of their products. They would be out on a legal limb if they claim more than a product can deliver.  Thus, it seems safe to assume that the effects of a vaccine will last longer than the suggested time between booster shots. Updates are needed by the immune system so that its protective inventory is always up-to-date and prepared; it gets updated every time the horse is in contact with an infecting agent as well as every time he gets booster shots. A pretty good protection scheme, that – but the manufacturer must make sure his updated vaccine is available and delivered before it’s obsoleted by further mutation. Immunology is a pretty complicated science, wouldn’t you say?

    So we can see why manufacturers “push” repeated shots – often, today’s formula is updated from that of an earlier version, and while he certainly is in business for profit, the manufacturer is also in business to keep our horses healthy – and so are our veterinarians. It’s obvious that veterinarians in general are very honest in not providing any products to horse owners that do not bring good value for their cost. Most believe in an item completely or they will not provide it to a client or patient. Certainly, there are exceptions to that observation, but in general, our veterinarians take pains to provide an extra level of service to us and to our horses, and in so doing, many will join the manufacturers in “pushing” regular boosters.  

    Well, there you have it. A dichotomy. On one hand it seems to appear that we’re over-vaccinating, at significant cost to ourselves and possible harm to our beloved horses. But on the other hand, pharmaceutical manufacturers and veterinarians need to be sure that they are providing more than just adequate care, and doing so in a timely fashion.

    It is a dilemma. We can second-guess them all day long, but who among us would risk arbitrarily tweaking the rules of the game, so to speak, when the stakes are so high? The take-home is that it is probably wise to provide booster shots to our healthy horses in order to keep them that way, but do the difficult research to determine how often your horse gets vaccinated and against what dangers. They should not be a cookie-cutter answers, like “annually” and “for everything”, but rather customized for your own horse’s circumstances. Remember, we are the ultimate decision-makers. If we think that giving yearly shots is too often, it’s easy to schedule them only every two years – or every three – or however frequently we deem is enough. Considering all the unknowns, one action seems to make good sense – discuss your specific situation in detail with your vet. There is a large fund of knowledge in every vet – we should all partake of it, and our horses are the beneficiaries.

  • Prebiotics in Horses

    Written By Dr. Kris Hiney

    Last month we discussed the use of probiotics in horses, including the definition and types of probiotics, their effectiveness, and when their use might be warranted.  This month we will address a closely related and often misunderstood topic: prebiotics.  The use of both of these feed additives may work synergistically to promote digestion in your horse, keep his immune system in top shape and allow him to face the various stressors which may be present in his life.

    As opposed to probiotics, prebiotics are not live organisms.  Rather, they are chains of specific types of carbohydrates which promote the growth of organisms which are beneficial to the well-being of the host.  Prebiotics are derived from a variety of products, including milk, fruit, vegetables and fermentation byproducts.  These are typically short chains of fructo-oligosaccharides (FOS), which are a mix of fructose and glucose, mannose oligo-saccharides (MOS) or galacto-oligosaccharides (GOS).  Simply stated, oligosaccharides are shorter chains of carbohydrates or saccharides (sugars) as compared to polysaccharides such as starch, glycogen of cellulose.  For a review of carbohydrate terminology, please see: Equine Carbohydrate Disorders Part 1. Because of the type of bonds joining the carbohydrates together, prebiotics are not able to be enzymatically digested in the stomach and small intestine.  Instead they provide substrates for fermentation of a specific group of bacteria and thus allow them to flourish.  It may be helpful to think about prebiotics as providing food for the good types of bacteria, rather than feeding your horse.   In ruminant animals such as cattle, sheep and goats, they have a direct effect on the rumen microflora, while in monogastrics and hind gut fermenters such as the horse, prebiotics pass to the hindgut where they exert part of their beneficial effect.   Horses also have a substantial microbial population in the foregut as well.  While the use of prebiotics in gastric health of the horse has not been explored, it does appear promising as a potential tool in maintaining stomach health.

    So why would you have to feed the bacteria?  Certainly a horse on a high forage diet would have adequate nutrient delivery to those microbes, correct?  Well, different types of organisms utilize different substrates for food.  If there is more food available for one type, they will be more successful and reproduce at a higher rate.  Cellulytic bacteria are responsible for fermentation of the fibrous portion of a horse’s feed and are typically associated with a higher pH in the gut.   However, amylotic bacteria prefer substrates such as sugars and starches. When we over feed concentrate to our horse or forages containing more rapidly fermentable sugars, these amylotic bacteria flourish and can produce negative by products for the horse.  Prebiotics typically provide substrate for more beneficial strains of bacteria including bifidobacteria (found more in humans), lactobacillus and lactate utilizing bacteria.  The use of prebiotics has shown to be effective in preventing the rapid and detrimental shift in bacterial population which occurs when horses are overfed concentrates. Now certainly it would never be advisable to subject our horses to a rapid increase in carbohydrates.  However, we could think of supplementation of prebiotics during periods of dietary adaptation, shifting to a new feed source or when starting to graze in the spring as a potential way to modulate gut microflora. However, supplementation of prebiotics would not be an alternative to slow controlled adaptation to new diets.

    Prebiotics may have more benefits than just helping to increase fermentation or stabilize the population of the hindgut.  While not digested in the small intestine, prebiotics help prevent the colonization of pathogenic bacteria such as Salmonella and E coli.  Doing so improves the overall health status of the animal.  They do so by binding to the carbohydrate receptor sites on the bacteria which are used to bind to intestinal epithelial cells. By “tricking” bacteria into binding to these oligosaccharides, they are prevented from binding to epithelial cells and proliferating. Promoting the growth of the beneficial bacteria may even limit the growth of pathogenic bacteria.  Bifidocacteria and lactobacillus possess their own bactericidal/anti-microbial effects against harmful bacteria. The “good” type of bacteria may also release enzymes which destroy the toxins produced by pathogenic bacteria.  Clearly it is easy to see why the feeding of prebiotics has gained much attention in feeding production species as an alternative to antibiotics.

    In addition to these direct effects on bacteria, immune-stimulatory effects of prebiotics have been observed in a variety of subjects. These appear to be not only in response to viral or bacterial challenge, but even with allergen stimulated immune responses. Human infants supplemented with prebiotics which mimic those found in breast milk developed fewer infections compared to those not receiving prebiotics.  There is also some evidence that intestinal epithelial cells may be able to transport prebiotic oligosaccharides, putting them in direct contact with cells of the immune system.  In an in vitro equine study, peripheral blood mononuclear cells (lymphocytes, macrophages) showed an increased immune response when these cells were cultured in the presence of GOS and FOS. When these same cells were challenged with LPS, the effect was even more pronounced in cells cultured with FOS and GOS.  The use of prebiotics may be a tool in helping to develop the immune system of neonatal foals, as has been proposed in other species.    Finally, prebiotics may serve as natural anti-oxidants themselves. In part this could help explain their immunomodulatory effects as well.  Therefore, consider using prebiotics when the animal might be undergoing periods of stress, as stress typically weakens the immune system.

    Even beyond their ability to affect the population of micro-organisms in the hindgut or stimulate the immune system, prebiotics may also help with insulin sensitivity.  This has been shown in dogs, veal calves, rodents and humans.   The effect is believed to be due to the alteration of fermentation in the hindgut, resulting in a shift in the ratio of volatile fatty acids which are produced. In obese horses supplemented with short chain FOS, a modest improvement in insulin sensitivity was observed after 6 weeks.  Prebiotics may serve as an aid to restoring insulin sensitivity, but certainly should not replace diet modifications or a sound weight loss program.

    Certainly the addition of prebiotics to the human food supply is increasing, and a number of products designed for use in pet foods and production animals point to the value of this natural foodstuff in promoting the health for all. There do not appear to be any risks associated with feeding prebiotics, and the number of proven health benefits is quite expansive.  The evidence for their effectiveness in improving the health and well-being is so many species of animals is substantial.  So if your horse needs help with digestion, stress, his immune system or even insulin resistance, consider a prebiotic.

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