Immunity Against the Elements
The term “immunity” is a bit misleading. We use the word immune to indicate “can’t get sick” and usually we mean from a pathogen of some sort (virus, bacteria, fungus, etc.). Yet the immune system itself has a scope well beyond whether or not you or your horse “gets sick”, as the immune system encompasses all the tissues, secretions, and mechanisms that create barriers to entry of pathogens, physically protects sensitive tissues from damage in the first place, limits spread of injury or illness, creates pain to reduce the use of injured/infected tissues (since use often leads to spread of damage), and changes blood flow in the body in response to illness or injury. The aspect of the immune system that accounts for specific pathogens and in some cases can lead to reduced chance of having disease symptoms (what we’d casually call “immunity”) really only kicks in when all the other immune system components have failed to prevent the pathogen from thriving in the body.
Overview of How the Immune System Is Organized
1st line of defense… prevent entry. This includes skin coating underlying sensitive tissues, mucous membranes in the mouth and respiratory tract trap particles and pathogens physical, acidic secretions in the stomach can kill ingested pathogens, urine washes pathogens down and out the urethra, etc.
2nd line of defense… isolate and eradicate anything suspicious. This includes increased blood flow to injured/infected tissues, swelling and pressure at the site, pain that limits mobility/use, fevers or localized temperature increase, white blood cells accumulating to consume and digest pathogens or contamination, etc.
3rd line of defense… locate and destroy the pathogen that has taken residence inside tissues and body fluids. This is the complicated one. This includes your immune system cells having to learn to “recognize” pathogens and differentiate them from the normal human/horse cells. Once located, these cells also have to “formulate a plan” of attack to determine what other immune system cells and antibodies are needed to fight the pathogen. After these phases, finally the immune cells and antibodies they produce can actually start destroying the pathogen. From there, these cells have to “remember” that this pathogen is a problem so that in the future the immune response can be faster – hopefully destroying the pathogen before it makes you/your horse feel sick.
This 3rd line of defense is how vaccines can be used to help effectively prevent illness. Instead of waiting for you or your horse to get exposed to a pathogen naturally, then wait for the immune system to recognize, formulate a plan, and actually start fighting the pathogen – all the while the pathogen has been multiplying, infecting tissues, and making you or your horse feels sick – vaccines introduce either a dead or weakened version of the pathogen so that the immune system can go through the needed steps without much risk of the pathogen actually causing symptoms. Further, the immune system will now remember this pathogen for the next time it enters the body and will start the attack quicker and with a stronger immune response than with the first exposure to the vaccine.
Signs Your Horse’s Immune System Isn’t Operating Properly
Cornell University College of Veterinary Medicine advises that clinical conditions that may indicate immunodeficiency include:
- two or more episodes of pneumonia within 1 year
- infections with opportunistic organisms
- multiple sites of infection (pneumonia + sinusitis)
- recurrent pyodermatitis (“hot spots” of hair loss, crusting or wet skin lesions, may be itchy), deep skin or organ abscesses
- single episode of meningitis or osteomyelitis (bone infections that include both the inner and outer layer of bones)
- two or more months on antibiotics with little or no affect
- failure to gain weight or grow normally (despite appropriate diet for phase of life, body type, and training)
- recurrent infections with a history or primary immune deficiency in the blood line
On the other side of the spectrum, immune systems can be overresponsive to pathogens, which can also be dangerous to the horse if overly aggressive responses lead to excessive changes in blood flow, intense swelling, over productive mucus accumulation, or accumulation of antibody-pathogen complexes build up in organs and blood vessels. Examples of over reactive immune responses include allergies (with the most dangerous being anaphylaxis), hypersensitivities, systemic shock in response to a pathogen, autoimmune disorders (immune system attacks your normal tissues as if they were pathogens), chronic inflammation with or without cause (Tizard, 2019). Often over reactive immune responses are correlated with long-term exposure to mild levels of pathogens or with frequent acute immune challenges or back-to-back stressful events.
Management Techniques to Support Normal Immune Function
Support your horse’s immunity with appropriate vaccines and deworming plan for your horse’s environment, age, and risk level. Talk to your veterinarian to discuss both core and risk-based vaccines for your horse and to determine the best schedule of vaccines you should employ given your horse’s specific needs. If your horse is immunocompromised, discuss in detail with your vet the risks and benefits of vaccinating, and be sure you understand what you need to know if your horse isn’t vaccinated properly (chance of diseases, signs of diseases, risk of spreading diseases, how lack of vaccines will limit your horse’s ability to travel and their competitive potential, etc.). Further, adhering to guidelines for fecal parasite checks and deworming when needed with recommended products, as well as being aware of signs of internal and external parasite infestations, should all be part of reducing your horse’s immune stress.
Some at home immune support recommendations include providing a clean, safe environment for your horse to reduce exposure to irritants and reduce the change of injuries and bodily stress. This includes reducing dust (especially in the air and in feed/hay), ensure good airflow in housing, cleaning stalls regularly to reduce ammonia fumes and contact with fecal matter, locating manure pits away from main barns and pasture areas, harrowing pastures to break up fecal piles on sunny warm days, having durable safe fencing, pastures and barns with safe footing and no locations where horses can get trapped or bottlenecked with other horses, stalls that are conscientiously designed to reduce sharp spots or friction, feeders and hardware that are oriented to reduce injuries, monitoring for dangerous plants in hay and growing in pastures, and providing shelter during wet, cold weather and during hot, humid weather.
Try to limit repeated exposure to known risk chemicals, which could include common topical medical treatments, fly sprays, pesticides or herbicides – basically being conscientious of any product with health warnings on it and especially if it states something about not giving the product to animals intended for slaughter. Many warnings are based in particularly on human risk (so good for you to be aware of too!), but keep in mind that horses have the potential to live upwards of 40 years and some products are able to accumulate in your horse’s body over time. If a lower-risk option is available, consider making a switch when possible.
Along similar lines, be willing to re-evaluate long-term medications to ensure that over time they are still appropriate, effective, and not causing harm or side effects that outweighs their benefits. This is definitely a conversation to have with your veterinarian. Sometimes medication options change, over-the-counter treatments come available, or we just get in the habit of giving some drug when it’s no longer fitting the bill. A good rule of thumb whenever your horse is prescribed a long-term medication is to ask the vet for a time line for when you should re-discuss the medication for its fit for the condition. And if you don’t feel confident the medication is addressing the issue or becomes less effective over time, check in with your vet to be sure there’s not another option or additional health consideration being overlooked for your horse. The unfortunate truth is most medications have side effects that could create additional biological stress for your horse, so be sure medications stay worth their side effect.
While we’re talking biological stress, keeping horse in a calm, relaxed state is also beneficial to immune functions. Fun fact… when in a heightened stress, fight-or-flight status, your horse’s energy is redirected away from healing from injuries, repairing damaged tissues, recovering from illnesses, or digesting and absorbing food (which means reduced nutrient availability). Instead, energy is put towards survival for the short-term, which for a horse means fueling all activities that would be related to bolting. Blood flow increases to legs and chest (and away from digestive tract), increased heart rate, increased respiration rate, increased blood glucose to fuel the sprint, sweating to regulate temperature, inability to focus, and hyperaware of threatening stimulus. All this equates to a horse who is ready to hurt themselves and not able to repair itself. Luckily, outward signs of stress like this are usually temporary and dissipate when the “threat” is over, but chronic low level stress can produce chronic low level effects like this, reducing your horse’s immune function and simultaneously increasing the risk of injury and illness. So let’s look at some ways to modulate stress on a daily basis.
Beyond Bugs Bugging
Biting and swarming bugs can create non-stop agitation, so methods to lower exposure and agitation by insects goes a long way to easing daily stress levels. As mentioned, cleaning stalls regularly, harrowing fecal piles in pastures, and keeping manure pits away from barns and pasture traffic all help with air quality and reduce parasite exposure, but these practices also reduce insect accumulation around horses. In addition, find an effective fly spray for your area, which may require some trial and error, and apply at regular intervals. If possible, seek an herbal or low risk chemical blend to reduce long-term exposure to concerning chemicals. Consider automatic sprayers or insect control systems for indoors, and hang fans wherever horses are stationary (stalls, run-in sheds, trailers, etc.), as moving air helps reduce insect landing stability they need for biting. Consider fly-predators, fly traps, or bug lights, and review their recommendations for time-frames of effectiveness, when to employ them for best results, and if they have limitations that won’t meet your needs. Plus, physical barriers on your horse – fly sheets, fly masks, fly boots, etc. – may be a good option for turn-out. Be sure the material is breathable, strong enough to hold up to pasture life, and try to aim for duel benefit by getting coverings that are UV resistant and/or able to cover sensitive areas like white patches of fur or sensitive noses.
Keep in mind that reducing exposure to insects isn't just about the physical annoyance being reduced... insects transmit diseases, reduce blood volume, cause allergic reactions, and create local swelling and itching that can lead to scratching (furthering inflammation and risk of tissue damage).
Too Much... Too Soon... Can't Take It Anymore!!
Other ways to reduce stress include developing conscientious training, competition and healthcare schedules to allow time for recovery between notable events. In the event of injuries or illness, allow enough time for full recovery before returning to training or competition. Work with your vet to know what benchmarks of recovery to look for to know when it’s appropriate to get back to regular schedule to reduce re-injuring or promoting a secondary infection. Spread out scheduled stressful events so that your horse isn’t bombarded with multiple systems being impacted by changes and challenges at the same time. Things like vet visits, farriers, vaccinations, deworming, diet changes, new barns, new turn-out schedules, abnormal travel, etc., should be spread out with time in between to help reduce chances of allergic reactions, behavior issues, appetite/water intake changes, and/or colic. Providing a quiet, peaceful environment to help your horse be able to anticipate their day, have a regular sleep schedule, and be confident of their environment helps horses be mentally more stable and compliant.
It’s Getting Hot in Here… So Please Take Off My Blanket…
Address temperature regulation for your horse, in particular so they don’t overheat. Overheating is much more common and harder for horses to naturally correct than being cold. Excessive blanketing, lack of shade, poor airflow, dehydration, obesity, and training at levels or in temperatures the horse isn’t acclimated to are all common causes of overheating. If a horse is overheating, cool them off quickly with cool water over their head, neck, back, and rump, and continue running water until the horse is cool to the touch. Allow the water to evaporate on its own instead of scraping or toweling off, as evaporation relieves the body of more heat as the water dissipates. Place the horse in a shaded cool place with a fan, check vitals and body temperature, and monitor the horse for dehydration and colic symptoms (Marlin, 2014).
On the other hand, most horses can handle cold dry air well, but be cautious with very young, very old, very thin, body clipped, or fully un-acclimated horses (like moved from Florida to Montana in December). Horses are less adapt at cold wet weather and may be unable to maintain sufficient body temperature if it is raining and cold. Horses hold temperature better in snow than in cold rain, in fact, but keep in mind what environment your horse is acclimated to when making decisions about housing and blanketing, as all horses will be more sensitive with very drastic changes in air temperature (up or down) over short periods of time. Be prepared to make adjustments to reduce temperature stress and set realistic plans for how and when to turn-out, stable, and blanket your horses.
Getting a Diet Advantage
For horses with impaired or imbalanced immune systems, it’s important to provide appropriate feed for the condition to address both the immune system’s operation and side effects of the immune issue. For instance, a horse with allergies may develop asthma, so using the diet to help suppress the allergic response is a portion of the needed changes, but the horse would also benefit from a diet that aids respiratory function as well. Another example would be for a horse with chronic infections who is on antibiotics, a diet that supports the immune system to help reduce the infection rate would be great, but we also need to address the hindgut function that will be affected by the antibiotic intake. This type of horse needs support on both sides so that the need for antibiotics is reduced, but also the microbiome of the hindgut is re-established and supported to help that horse be able to digest feed and absorb nutrients needed for the immune system to function (along with all other body processes). Choosing a diet to support immune dysfunction is wide ranging and ultimately very specific to your horse, its environment and training demands, and setting realistic goals for the diet. No… we can’t magically cure a decade of immune disorders that started at birth and have been exacerbated by poor management and high stress by adding in an herbal ingredient. The whole picture should be addressed and the diet formulated to help and not hinder your horse’s immune system to get back on track. Thus, talk to your vet and your Science Supplements nutritionist for advice on helping establish a supportive diet plan.
The Role of Vitamins, Minerals, and Amino Acids in Immunity
Seems simple, but being sure you’re providing vitamins and minerals that are basic requirements of tissue growth, integrity, and repair can be overlooked in the world of immune system concerns. Complete feeds and commercially formulated feeds should provide information on vitamins and minerals included, but establishing what is provided by forages (pasture, hay, etc.) and water sources can be more difficult to access, forages sources change on a regular basis, and even being on the same pasture does not translate to consistent vitamin and mineral level availability throughout the year. Thus, for horses with any question of access to basic nutrition needs, providing vitamins and minerals should be ensured with balancers or immune supplements with a wide range of vitamins and minerals included. In particular, some vitamins and minerals have specific roles in immune function and tissue integrity, such as a variety of B vitamins are integral for metabolism, tissue quality, and red blood cell formation, Vitamin C, E, and selenium are powerful antioxidants (more on that later), and Vitamin D and zinc both provide immune support and have key roles in tissue development (National Research Council, 2007).
Amino acids (building blocks of protein) should also be provided to ensure minimum requirements are met by the diet, or else the ability to rebuild and repair damaged tissues can be compromised. Horses without basic amino acid needs met won’t be able to recover from injury or illness without breaking down current protein tissues (muscle, organ walls, etc.) and will neglect building protein rich tissues and tissues that are under constant turnover (skin, hair, hooves, lining of the respiratory and digestive tract, new muscle, etc.) in order to fuel the recovery process. Keeping in mind our earlier discussion about the 1st line of defense of the immune system is to be a barrier to entry of pathogens, allowing skin and the respiratory tract tissues to become compromised or slowing the healing of wounds due to an amino acid shortage can open up horses to infections. Also, like vitamins and minerals, some amino acids have specific importance and/or immune system rolls, so including them in your horse’s immune support can be additionally beneficial. For instance, L-Lysine is the most well understood limiting amino acid, meaning that if the diet doesn’t provide enough L-Lysine then all other protein production is impaired, and thus a diet low in L-Lysine will result in slow tissue healing and thinning of protein rich tissues (National Research Council, 2007). Another example, L-Cysteine helps regulate mucus production in the respiratory tract and has anti-oxidant and anti-inflammatory effects (Calzetta et al., 2018) and thus can be helpful for horses with allergies or respiratory conditions.
What are antioxidants?
Antioxidants are compounds that can counter the risk of damage to tissues and DNA by byproducts of metabolism and pollutants called reactive oxygen species (ROS). ROS are associated with the deteriorating effects of aging and diseases of the respiratory, cardiovascular, neurodegenerative, and digestive systems, as well as cancer throughout the body (Liu et al., 2018). Dietary components with particular antioxidant capacity include Vitamins A, C, D, and E and minerals selenium, manganese, zinc, and copper, as well as compounds like rosehips, Echinacea, spearmint, lycopene, polyphenols, and thioredoxin (abundant in yeast cell walls). Antioxidants are included in immune support supplements to help prevent damage to cells and DNA, but they also support repair of existing cell damage by helping alleviate chronic inflammation that exacerbates ROS creation (Liu et al., 2018).
Inflammation is a natural response of the immune system to damage or disease, and inflammation is a wonderfully helpful cascade of events that can ultimately drive the healing of tissues almost independently. Inflammation at its core is increase in blood flow to an area of need, which delivers nutrients, immune cells that clean and repair the area, heat to impair pathogens and speed your/your horse’s metabolism towards repair, and simply increasing blood flow can literally “wash away” debris and pathogens from an area and into tissues and organs that can remove the physical remains of the injury/infection. We don’t always view it this way, but inflammation also creates pressure and therefore pain – which is a natural means of limiting the continued use of a damaged/infected tissue. When something hurts, we’re less likely to continue on with the actions that caused the injury and/or we’re more likely to rest the area – which gives time to heal, reduces scar tissue formation, shortens the repair process, and leads to better quality tissue creation.
So if inflammation is a good thing, why include anti-inflammatory components in immune support products? The caveat is that short-term inflammation is generally a good thing because it promotes healing. However, some short-term inflammation is damaging due to its location, such as in asthma where the inflammation of the airways restricts air flow and can lead to systemic damage or even death in severe cases. Another example of damaging short-term inflammation would be in blood flow to the hooves, where inflammation causes restricted blood flow to the hooves and the laminae in particular can suffer permanent damage and lead to laminitis. Providing regular anti-inflammatory support to horses with history of conditions that are associated with acute, risky inflammation can reduce sudden symptoms with wide ranging consequences.
Further, long-term inflammation – and particularly that which is associated with impaired opportunity to actually lead to “healing” – is counter-productive and eventually leads to scar tissue, loss of tissue use, and promotes damage to other systemic tissues. What I mean by impaired opportunity to actually heal is in scenarios like auto-immune diseases where the body’s immune system is actually attacking normal tissues, which are then rebuilt, only to be attacked again, and then rebuilt again. This cycle is detrimental and leads to massive scar tissue creation – along with chronic pain and eventual loss of tissue use. Reducing inflammation here suppress the tissue damage and need to rebuild constantly, reducing pain and allowing body resources to be better used.
Another example of impaired opportunity to heal would be in tissues that do not have the opportunity to repair when damaged – such as in arthritis. Cartilage cannot heal itself, so when cartilage is damaged for any reason, it won’t be able to return to cartilage and instead becomes bone. Bone in a joint space creates hard, scraping contact within the joint, and this leads to chronic inflammation, pain, swelling, and less mobility of the joint. Additional inflammation leads to stiffening of the joint, reduced blood/synovial fluid flow through the joint, impaired nutrient delivery/waste removal to the joint, and eventually more scar tissue and conversion of cartilage to bone. Thus, in the case of arthritis, reducing the inflammation helps maintain the quality of the tissues, improves joint health to maintain mobility, reduces the escalation of joint disease, and keeps horses mobile and more comfortable.
Common anti-inflammatory ingredients are omega 3’s, with marine sources (EPA, DHA) being of higher potency and immune promoting evidence that plant sources (ALA). Also, MSM provides anti-inflammatory support while also supplying bioavailable sulfur for skin and hoof tissue synthesis, making MSM a good option for horses with chronic laminitis or skin conditions. Some common joint support compounds like glucosamine have anti-inflammatory effects particular to joints, but also herbal ingredients found in joint support and immune support supplements have evidence of anti-inflammatory effects systemically, including boswellia, rosehip, and Echinacea.
Digestive Support = Immune Support
The digestive system is the gateway to the body. Early in this topic we discussed that the lining of the digestive tract was part of the 1st line of defense of the immune system, which makes sense when you consider that we and our horses consume food with pathogens and contaminants all over it on a very regular basis. It’s inevitable that your horse will eat food and drink water tainted with bugs, viruses, bacteria, fungus, dirt, pollen, pollution, chemicals, molds, toxins, and the like. And yet, all in all the risk of getting sick this way is relatively low considering the vast amount of food and water consumed each day. This is because…
- Horses are generally selective about what they’ll eat and constantly assess their food and water for what they consider abnormal (hence… able to select the blades of grass from amongst the weeds, refuse to drink sour water, decline feed they recall caused them pain, etc.)
- The stomach is a low pH environment, and this acidity kills most living pathogens. Keep this in mind for those chronic ulcer treatment horses! Raising the pH for ulcer treatment has an increased chance of pathogen survival, so be diligent looking for secondary diseases, treat ulcers in the quickest methods possible, and avoid long-term “prevention” with powerful drugs that raise pH artificially. Find a more natural solution that doesn’t permanently change acid creation for the chronic ulcer horse.
- The small and large intestines (hindgut) have a very high proportion of immune tissues that house immune cells. These patrol tissues are constantly evaluating what is being absorbed by the digestive tract and are on the lookout for pathogens that cross the border.
- The microbes that live in the hindgut help prevent the growth of dangerous microbes. Imagining that there is a steady intake of feed material into the hindgut, there is a finite amount of room for microbes to live and a finite amount of resources available, so if they good guys are living and thriving, this naturally suppresses the opportunity for bad guy growth. The danger zone is when horse diets change too quickly, when intestinal parasites are abundant and/or rapidly killed off (leaving room for microbial fluctuations), and certainly when antibiotics are given. These events leave opportunities for pathogenic microbes to surge and create diseases stemming from the GI tract.
Supplement components that support the immune function of the small intestine and the hindgut environment can help prevent disease introduction from contaminated feed and water intake. Compounds like mannaoligosaccharides (MOS) have been shown to strengthen the GI tract wall cell barrier (preventing pathogen access) and to activate the immune response of the GI tract (Ofek and Beachey, 1978). Betaglucans can bind toxins in feed and prevent them from affecting the horse, regulate water fecal loss (reducing dehydration risk), regulate immune responses to pathogens, and act as antioxidants (Duss and Nyberg, 2004; Jacobs et al., 2017; Kofuji et al., 2012; Paap and Roberti, 2014). Fructooligosaccharides (FOS) help support beneficial microbes and stabilize their population even with sudden diet changes, as well as helping them compete with pathogenic bacteria like E. Coli (Berg et al., 2005; Campbell et al., 1997; Respondek et al., 2008; Roberfroid 1997; Flickinger et al., 2003). High numbers of live, protected probiotics can help stabilize the hindgut microbial population and improve digestion, leading to better nutrient uptake and availability (Elghandour et al., 2016; Garber et al., 2019; Glade and Biesik, 1986; Lattimer et al., 2002; Medina et al., 2002; Pagan, 1990).
The immune system affects every component of horse health and livelihood, and for the competition horse with higher than average immune challenges and stress, supporting the immune system’s function can alter the outcome of a show, the show season, or an entire career. Particularly for horses with chronic immune struggles, take an inclusive look at your management, healthcare strategy, and dietary support to help your horse find a better balance and ease recurrent symptoms.
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