Gut Health - Aspects of bad behaviour and how to fix it
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By Bill Vandergrift, PhD
When performance horses behave or react in ways that are less than desirable, we as trainers and handlers try to figure out what they are telling us. Is there a physical problem causing discomfort, or is it anxiety based on a previous negative experience? Or, is the bad behaviour resulting from a poor training foundation leading the horse to take unfamiliar or uncomfortable situations into their own hands? This usually triggers the fright and flight reflex instead of relying on the handler for direction and stability.
Often when the most common conditions that cause physical discomfort are ruled out, it may be tempting to assume that the bad behaviour is just in the horse’s head or that the horse is just an ill-tempered individual. In my experience, most unexplainable behaviour expressed by performance horses is rooted in the horse’s “other brain,” otherwise known as the digestive system. In this article, I will explain what causes poor digestive health, the link between digestive health and brain function, and what steps can be taken to prevent and/or reverse poor digestive health.
Digestive health
While most trainers are familiar with gastric ulcers, symptoms and common protocols utilised to heal and prevent them, there still remains a degree of confusion regarding other forms of digestive dysfunction that can have a significant effect on the horse’s performance and behaviour. In many cases, recurrent gastric ulcers are simply a symptom of more complex issues related to digestive health. Trainers, veterinarians and nutritionists need to understand that no part of the horse’s digestive tract is a stand-alone component. From the mouth to the rectum, all parts of the digestive system are in constant communication with each other to coordinate motility, immune function, secretion of digestive juices and the production of hormones and chemical messengers. If this intricate system of communication is interrupted, the overall function of the digestive system becomes uncoupled, leading to dysfunction in one or more areas of the digestive tract.
For example, a primary cause of recurrent gastric ulcers that return quickly after successful treatment with a standard medication protocol is often inflammation of the small and/or large intestine. Until the intestinal inflammation is successfully controlled, the gastric ulcers will remain persistent due to the uncoupling of communication between the stomach and lower part of the digestive tract.
How do we define digestive health? Obviously, digestive health is a complex topic with many moving parts (figuratively and literally). The main parts of a healthy digestive system include, but are not limited to 1) the microbiome, 2) hormone and messenger production and activity, 3) health of epithelial tissues throughout the digestive system, 4) normal immune function of intestinal tissue and 5) proper function of the mucosa (smooth muscle of the digestive tract) to facilitate normal motility throughout the entire length of the digestive tract.
Microbiome is key
A healthy and diverse microbiome is at the centre of digestive health. We now recognise that reduced diversity of the microbiome can lead to digestive dysfunction such as colic and colitis, development of metabolic disorders such as insulin resistance, reduced performance and increased susceptibility to disease. Research efforts leading to greater understanding of the microbiome have recently been aided by developing more sophisticated techniques used to identify and measure its composition in horses, laboratory animals, pets, livestock and people. While these research efforts have illustrated how little we really understand the microbiome, there have been significant discoveries stemming from these efforts already. For example, a specific bacteria (probiotic) is now being used clinically in people to reverse depression resulting from irritable bowel syndrome (IBS). Bifidobacterium longum NCC3001 reduces depression in IBS patients by directly affecting the activity of the vagus nerve which facilitates communication between the brain and the digestive tract. It should be noted that Bifidobacterium longum NCC3001 has been demonstrated to be more effective at reducing depression in IBS patients than antidepressant drugs commonly used in these same cases. While we do not commonly recognise clinical depression as a physiological condition in horses, the same mechanisms that affect the function of the vagus nerve and brain chemistry in IBS patients can affect a horse’s behaviour and reactivity due to intestinal dysfunction, resulting in a horse that bites, kicks, pins its ears or otherwise demonstrates hyper-reactivity for no apparent reason, especially if this behaviour is a recent development.
One case in particular I dealt with years ago that had underlying suggestions of depression in a horse, and underscores the importance of a diverse and healthy microbiome for performance horses, was a horse that had been recently started in training and was working with compliance on the track. The problem was this horse seemed to be unable to find the “speed gear.” The trainer had consulted with various veterinarians, physical therapists, chiropractors and others in an attempt to pinpoint the cause for this horse’s apparent inability to move out; and it was everyone’s opinion that this particular horse had the ability but he simply wasn’t displaying the desire. In other words, he was “just dull.” After reviewing this horse’s case and diet, I had to concur with everyone else that there was no obvious explanation for the lack of vigor this horse displayed on the track even though his body condition, muscle development and hair coat were all excellent. Despite any outward signs of a microbiome problem other than the horse’s “dullness,” I recommended a protocol that included high doses of probiotics daily, and within 10 days, we had a different horse. The horse was no longer dull under saddle; and when asked to move out and find the next gear, he would readily comply; by making an adjustment to the microbiome, this horse’s career was saved.
There is always a change to the microbiome whenever there is a dysfunction of the digestive system, and there is always digestive dysfunction whenever there is a significant change to the microbiome. Which one occurs first or which one facilitates a change in the other may be dependent upon the nature of the dysfunction, but these two events will almost always occur together. Therefore, efforts to maintain a viable and diverse microbiome will reduce the chances of digestive dysfunction and increase the speed of recovery when digestive dysfunction occurs.
Leaky gut
Even though the physiological basis of leaky gut has been understood for some time, leaky gut has not been a condition recognised to affect behaviour, performance or health in horses until recently. Today, leaky gut is quickly becoming a recognised dysfunction of the digestive system that has a multitude of negative effects on the overall well-being of horses including allergies, insulin resistance, uncharacteristic behaviour, picky appetite and reduced performance. As illustrated in Figure 1, leaky gut refers to a breakdown of the structures, referred to as tight junctions that hold adjacent intestinal cells together.
When the small and large intestines are healthy, the tight junctions between individual intestinal cells remain closed, forming a barrier between the inside of the intestinal lumen and the inside of the horse’s body. This barrier normally serves as a very important function by preventing complex molecules such as undigested proteins and carbohydrates as well as pathogenic and non-pathogenic bacteria from “leaking” through the intestine and entering the horse’s blood stream. Also note in Figure 1 that as you move your focus from left to right in the diagram, not only do the tight junctions become open, but the intestinal cells become more and more inflamed, eventually leading to total breakdown of the intestinal cells themselves. At this point, you not only have leaky gut, but now the condition has progressed from a leak to a flood, so to speak. This illustrates that the severity of leaky gut can vary from mild to severe with increasing severity also being associated with increasing intestinal inflammation.
Figure 1. Basic Physiology of Leaky Gut
Image Courtesy of Kemin Industries.
As the severity of leaky gut increases, the communication between the different components of the digestive system is disrupted, and the coordination between the different sections of the digestive tract becomes uncoupled. The production of hormones such as serotonin and dopamine is altered, which has a direct effect on digestive function and brain function concurrently. This is one of the most obvious reasons why intestinal inflammation causes a horse’s behaviour and temperament to change. Inflammation of intestinal cells initiates a self-propagating process that stimulates additional inflammation of the intestine and initiates systemic inflammatory processes throughout the entire body. The self-propagating nature of intestinal inflammation is the reason why horses don’t just simply recover from it without assistance. In fact, I have worked with individual horses that have suffered from leaky gut for years based on their case history. The longer leaky gut has existed, the longer it will take to reverse in most cases.
In addition to leaky gut causing changes in behaviour and performance, leaky gut can also alter immune function and metabolic status. There is growing evidence that the initial cause of insulin resistance in many horses is in fact leaky gut. Intestinal inflammation causes a marked change in glucose homeostasis, which in turn reduces insulin sensitivity. Unfortunately, it appears that once insulin resistance is established, it is near impossible to reverse completely even if the leaky gut condition that caused it in the first place is successfully reversed.
Leaky gut is also a common trigger for allergies in horses. It is well known that the majority of the horse’s immune system is located in the intestine. When the intestine “leaks,” undigested proteins, bacteria and other immune-stimulating agents gain access to the bloodstream, thus putting the immune system on high alert. Many horses respond to this situation by presenting with multiple allergies, many of which are reactive enough to warrant immunotherapy (allergy shots). I often hear in these situations that “my horse is allergic to everything”; and in many instances, this would seem to be the case. Fortunately, by reversing leaky gut and removing these immune-stimulating agents from the horse’s body, many of these allergies simply disappear. Keep in mind that horses can in fact be truly allergic to certain feeds and environmental agents, and these allergies have nothing to do with digestive health. It is best to consult with an experienced veterinarian and nutritionist to distinguish between true allergies and those caused by an overactive immune system triggered by leaky gut.
As illustrated in Figure 2, leaky gut can be caused by many different “triggers.” In performance horses, the most common triggers for leaky gut are: 1) stress (physical and emotional), 2) intense exercise, 3) heat stress and 4) various medications. Of these, stress is the strongest trigger for leaky gut due to the fact that stress of any kind increases circulating levels of cortisol. Cortisol breaks down the tight junctions of the intestine, which in turn results in leaky gut.
Figure 2. Possible Factors Causing Leaky Gut in Horses
Preventing and reversing leaky gut
Almost all performance horses will present with digestive dysfunction or leaky gut at some point in time in their career. The reason is simple: stress is the strongest trigger for leaky gut, and all performance horses experience stress to one degree or another. Unfortunately, there is no exclusive marker for leaky gut at the present time. Researchers are getting close to developing a reliable diagnostic test for leaky gut as this article is written, but in the meantime it is best to detect digestive dysfunction and leaky gut by evaluating changes and observing symptoms presented by the horse. A partial list of symptoms to look for includes: a) not performing to the previous level or level that is expected, b) change in personality (e.g., grouchy or “leave me alone” behaviour, c) resistance to leg aids especially on right side (right dorsal colon is often inflamed), d) backing ears or biting when being saddled especially when the cinch is tightened, e) dull, f) prefers to eat hay rather than grain, g) manure has a funny odor or consistency, h) low fecal pH (herd specific), i) constantly shifting weight from one hind leg to the other in the stall, j) tight and “sunk in” in flank area, k) tight in back and hamstrings, l) eating a lot of grain but not gaining weight, m) dull coat and/or skin disorders, n) poor hoof quality, o) multiple allergies, p) improves while on omeprazole but quickly reverts when taken off, q) recurrent or chronic diarrhea and r) irreconcilable behaviour. (Note: No two horses will present with all of these symptoms or the same symptoms, but this list provides a guide for the most common symptoms to evaluate.
Since stress is the strongest trigger for intestinal inflammation and leaky gut, steps should be taken to remove as much stress as possible. For example, paying attention to biosecurity measures, transporting at times and with methods that reduce stress, adjusting training schedules to avoid heat stress and overexertion are things that can be done to reduce stress. Keeping forage (hay and/or pasture) in front of horses 24/7 is critical. Controlling the amount of grain-based feed fed per day can help in many cases. As a guideline, if you are having to feed more than 7 kgs (or 15 lbs) of grain per day to maintain a horse’s condition and energy level, you should suspect digestive dysfunction as one of the reasons so much feed is required.
If you suspect your horse is presenting with leaky gut, how can you help reverse it? Begin by continuing to provide “good quality” forage 24/7 and utilise a high-fibre, high-fat, low-soluble carbohydrate feed in place of a grain-based feed.
Second, utilise nutritional tools that are now available to stimulate closure of the tight junctions. These include nutraceuticals such as butyric acid, glutamine, bioactive peptides (plasma or colostrum), specific probiotics such as Bacillus subtillus PB6 and carnitine. There are products available currently that provide one or more of these nutraceuticals in the proper dosage.
Third, support a diverse and healthy microbiome with the use of probiotics and prebiotics. When selecting probiotics, numbers matter! It is preferred that any probiotic strain be dosed at a minimum of 1 billion CFUs (colony forming units) per day. Be sure to understand that this is per strain and not cumulative for a mixture of different probiotic strains. I would rather administer 10 billion CFUs of a single probiotic strain than 5 billion CFUs of a product containing a mixture of seven different strains. Additionally, for optimal effectiveness of any probiotic, it is imperative that it be dosed in combination with prebiotics such as yeast cultures, mannan-oligosaccharides, fructooligosaccharides, or inulin, for example. Prebiotics and probiotics work synergistically to alter the diversity and overall activity of the microbiome in a manner that provides far superior results compared to either one by itself.
Fourth, provide anti-inflammatory activity to the intestine with omega-3 fatty acids. Flaxseed, chia seed, hemp oil, and fish oil all contribute to reducing inflammation in the intestine. The omega-3 fatty acid EPA from fish oil is especially effective as an anti-inflammatory agent for the intestine. DISCLAIMER: In cases of severe leaky gut and severe intestinal inflammation, omega-3s may exacerbate the inflammation rather than reduce it. This will be noted within just 2–3 days by the horse presenting with notable diarrhoea. Additionally, omega-3s and coconut products are contraindicated for horses presenting with severe or chronic diarrhoea, as this is usually a reliable symptom of severe leaky gut, which is often made worse by these dietary components.
Fifth, include nutraceuticals to improve production of intestinal hormones and provide additional protection for intestinal cells. Possible choices include liquorice, slippery elm, aloe, arginine, citrulline, theanine, tryptophan, or alpha lipoic acid. Consult with a reputable supplement company for suggestions on which products and dosage are appropriate for your horse.