The digestive system of the horse and the effect of gut health on behavior
Written by Loni Loftus, Clinical Animal Behavior.
In this article, Loni Loftus, Clinical Animal Behavior, examines the mechanisms of the horse's digestive system and discusses how gut health in horses can directly affect behavior, including mental and physical health.
We have all heard the old proverb "No hoof, no horse"; however, the statement "No gut, no horse" is equally deserving of emphasis.
The horse is a non-ruminant herbivore; that is, it is specialized for feeding primarily on plants.
The horse's intestine or digestive system is considered the largest organ in the horse's body, and its health status has significant implications for the horse's physical and mental well-being.
From a biological perspective, the horse's digestive system consists of the mouth, including the teeth, tongue, and salivary glands, and the esophagus, and then reaches the stomach; after that, the small intestine and large intestine are present, which includes the very important cecum, and finally ends at the rectum and anus, where waste materials exit the body (Figure 1).
Figure 1 - A pie chart showing the average percentage of the digestive system's capacity that each section contributes.
A closer look at the overall process of stomach digestion in an empty state is approximately the size of a rugby ball and has an average capacity of 9 to 18 liters.
Food enters the stomach through the esophagus and through a one-way valve called the cardiac sphincter; this valve is the reason horses cannot vomit.
The entry of food stimulates the secretion of digestive juices.
Food, which at this stage is called "digestive contents," passes through the stomach for 20 minutes to 3 hours, and the larger the meal, the faster its transfer to the small intestine occurs.
In the stomach, food is hydrolyzed by acid, and protein digestion begins; alongside this, a small amount of soluble sugars and starch is also fermented.
Then, the digestive contents enter the small intestine through the pyloric sphincter; the small intestine consists of three sections: the duodenum, jejunum, and ileum, where all major starches, lipids (fats), and proteins are broken down.
This section is the main site for the absorption of nutrients from the horse's diet into the body for energy, growth, and repair.
At this stage, food is called "chyme" and moves along the small intestine through muscular contractions of the intestinal wall known as "peristalsis."
The small intestine is about 21 to 25 meters long, has a capacity of 50 liters, and the average time for food to pass through it is 45 minutes.
The large intestine consists of the small colon, large colon, and cecum.
The small colon is about 3 to 4 meters long but holds only up to 14 liters of liquid, while the large colon, with a similar length, can accommodate up to 82 liters of liquid.
Water and nutrients are absorbed from these sections of the digestive system.
The cecum holds about 35 liters of liquid, and food reaches this section about 3 hours after a meal.
The cecum is responsible for fermenting fibers such as alfalfa, and cellulose is broken down into volatile fatty acids, which are used as an energy source.
Waste materials are converted into feces and are expelled through the rectum and anus.
In order for this process to be carried out correctly and to provide the horse with sufficient energy, but not too much, attention must be paid to the design of the horse's digestive system, its mental (emotional) and physical health, as well as the amount of work or level of training of the horse.
A horse's stomach is the size of a rugby ball when empty and has an average capacity of 9 to 18 liters.
Nutrition for mental (emotional) and physical health is important due to the structure of the digestive system; the horse's stomach is relatively small compared to its body size, and the intestines are large enough to accommodate a significant volume of fibrous forage such as hay or grass.
For optimal performance, a horse must have free access to forage at all times, as this method simulates the horse's feeding pattern in a natural environment and maintains a continuous flow of low-energy forage in the digestive system to keep bowel movement regular, which reduces the likelihood of colic and also maintains a healthy pH in the digestive system, thereby reducing the risk of ulcers.
Providing forage freely also allows the horse to behaviorally recreate its natural environment by regularly chewing and eating long-stemmed forage; this contributes to maintaining a positive emotional state, as it has been shown that chewing reduces stress and increases the secretion of endorphins or "feel-good hormones."
Providing free forage along with access to a pasture where the horse can move freely, graze, and browse creates ideal conditions for keeping our domesticated horses; conditions that allow them to have a lifestyle as close as possible to their natural behavioral state.
Horses that live freely spend a significant portion of their time, about 46%, grazing and also exhibit a wide range of other behaviors, many of which are social behaviors with other horses.
However, unfortunately, many horses receive large amounts of high-starch concentrate feed divided into one, two, or three daily meals, while their forage intake has decreased and their access to movement and grazing has been limited.
This situation can not only affect the health of the digestive system but also impact the horse's daily time budget; a condition that may lead to undesirable behaviors such as excessive excitement, aggression, and repetitive behaviors including box walking, air biting, constant body swaying, cribbing, and similar behaviors.
Research has shown that keeping a horse in a stable for more than 13 hours a day is associated with the occurrence of abnormal oral behaviors and eating in horses.
These undesirable behaviors usually arise as a result of one of the following mechanisms, or a combination of them: a medical problem that causes physiological changes and/or pain; such as equine gastric ulcer syndrome excessive energy production due to the high nutritional value of feed and limited physical activity lack of time spent in the outdoor area lack of social interaction with other horses boredom leading to displacement behaviors, which can become repetitive and addictive fear/anxiety due to being kept alone in the stable or being punished for undesirable behaviors that have arisen as a result of the above factors.
Research has shown that keeping horses in a stable for more than 13 hours a day is associated with the emergence of abnormal oral behaviors and eating in horses.
Today, more than ever, we face the necessity of limiting the why and when of our horses' and ponies' time outside to manage a range of health issues, such as obesity, laminitis, PPID, and other metabolic disorders.
This issue can be challenging in that we must ensure that while meeting the natural needs of the horse, its physiological health remains in the best possible condition.
Similarly, meeting the needs of a horse that is resting in a box and recovering from injury or surgery can be just as difficult and yet important.
How can I ensure that I feed my horse in a way that supports both its physical and mental health?
If your horse does not require restrictions on grazing or being outside due to health issues, follow the traffic light system in Figure 2.
Figure 2 – Horse presence management system outside based on traffic lights If your horse requires restrictions or unusual management in its diet to help control weight or manage medical issues, any veterinary recommendations should be followed.
If grazing is to be restricted, socialization, movement, and foraging opportunities must still be provided for that horse.
Socialization opportunities can be created by providing a familiar and compatible companion to be with the horse both during grazing and in more limited times.
This can be done by using larger, grass-free paddocks for the simultaneous presence of more than one horse outside, or at least creating conditions where horses can be together and at a distance where they can reach each other to allow for mutual grooming.
Horses that are kept in a resting box may easily be deprived of both social companionship and access to foraging and grazing.
Horses can be encouraged to move more while outside, whether limited or unrestricted, using a tracking system; a system that provides them with specific areas for grazing, foraging, and curiosity, often executed in the shape of a loop or the number 8.
These systems can be designed in any way to accommodate the needs of the horses using them, and can include grass-free areas such as surfaces covered with wood chips and sand, hills, rolling spots, and treasure-hunting-like activities for foraging and finding treats to enhance environmental enrichment.
It is always important that the design and use of these systems are done carefully to enhance the health and well-being of all horses that benefit from them.
For horses and ponies that may have to stay in the stable longer or be restricted, hand-walking, if medical conditions do not prevent it, can be a good way to take them on grazing and foraging walks, often referred to as "picnic walks," to ensure their share of movement time.
This also gives them positive experiences to satisfy foraging behaviors and can simultaneously help foster a positive relationship between the horse and its owner.
Horses that are in a rest box may easily be deprived of both social companionship and access to foraging and grazing.
Whenever possible, providing a companion for a horse that is in a rest box is considered an advantage.
In some situations, larger shared indoor spaces or stables may be used to provide social companionship, and in other cases, an outdoor paddock can be arranged so that the resting horse can interact with other horses and/or see them within its line of sight.
Social interaction with others must be facilitated for these horses, part of which can also be achieved through "grooming" the horse by humans.
To reduce boredom and potential negative emotional states, including depression and frustration, providing a range of environmental enrichment tools for the restricted horse can be valuable.
These may include special horse balls, foraging games such as hiding carrots or similar treats in bedding for the horse to find, hiding or distributing feed in the non-grassy area of the paddock, introducing olfactory activities for the horses, conducting short and frequent hand exercises to stimulate the horse's mind, and providing puzzles for the horse to solve to receive low-calorie food rewards.
Overfeeding and excess energy from nutrition can be one of the common causes of significant behavioral problems related to exuberant or overly excited behaviors; behaviors that may manifest as kicking, sometimes accompanied by short whinnying, jumping, bolting, appearing overly nervous and alert, such as being frightened by multiple stimuli.
Although there are numerous other reasons that can cause such behaviors in horses — the most common alternative cause being pain — clinical animal behaviorists regularly encounter cases involving horses where an imbalance between energy intake and energy expenditure has led to unwanted behaviors and weakened the human-animal bond.
In such cases, it is crucial that the horse's diet is carefully calculated, monitored, and gradually adjusted to provide an optimal energy level and appropriate balance between macronutrients and micronutrients to maintain health and calm behavior.
After adjusting the diet, it is often necessary to conduct some training or retraining to eliminate learned behaviors and conditioned responses that have developed during periods of improper nutritional management.
It is important that this training is conducted with careful planning and by a qualified and certified clinical animal behaviorist to ensure that unwanted behaviors are replaced with new desirable behaviors without using aversive methods for the horse — whether through inflicting pain, fear, or frustration — methods that could otherwise be potentially dangerous for both the horse and the caregiver.
The list of professionals with valid certification from the Animal Behavior and Training Council is a way to find clinical animal behaviorists who specialize in horses and have the necessary qualifications, professional credibility, and sufficient experience.
The field of horse nutrition is not well-regulated or organized, and anyone can present themselves as a nutrition expert.
Look for someone who has a master's or doctoral degree in animal nutrition or equine nutrition, or consult one of the well-known animal feed companies for advice.
Do not hesitate to request credentials and evidence regarding the professional qualifications of a specialist to ensure that the advice you receive is right for you and your horse.
The information provided in this article is based on research conducted by the author.
Sources and attachments: Loni Loftus Source: Everything Horse