Are Horses Hindgut Fermenters

James Lee
• Wednesday, 16 December, 2020
• 18 min read

March 27, 2019April 15, 2020By Kentucky Equine Research Staff Horses rely on fermentation for optimal digestion of feed stuffs and energy production. Hind gut digestion, which occurs in the cecum and large colon, progresses most efficiently when horses are allowed continual access to forage and limited access to feed stuffs that could upset the pH of the cecum, including large grain meals.

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(Source: www.horsejournals.com)


Together, these microbes convert carbohydrate-based contents, essentially plant-based fiber, into volatile fatty acids (Via), which provide energy to the horse. If soluble carbohydrates, such as those found in large supply in grain meals, find their way into the hind gut, some lactate might be produced.

In many horses, this manifests as poor appetite, crabby disposition, recurrent colic, and onset of certain stable vices, such as stall-walking and cribbing. If a horse requires more than 5 lb (2.25 kg) of concentrate per day, divide total daily allotment into separate meals.

This is in contrast to ruminants, such as cattle, goats, and sheep, that are fore gut fermentors with a lumen and multi compartment stomach. Being a hind gut fermentor is a huge advantage to horses because it essentially gives them a second chance to process energy from feed that has already passed through the small intestine.

Cecal impactions with feed material are fairly common in post-foaling mares and horses that are hospitalized and treated with nonsteroidal anti-inflammatory drugs (phenylbutazone or fountain melamine). The convoluted course of the large intestine and its relative lack of any anchoring ligaments make it susceptible to displacements and twists.

Right dorsal colitis is an ulcerative condition that has been associated with administration of nonsteroidal anti-inflammatory drugs, and it usually leads to low blood protein concentration and intermittent colic. The small colon is the final part of the large intestine, and it is where fecal balls are produced.

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Examination of the large intestine without exploratory surgery can be difficult because of its sheer size and inaccessibility. Hind gut fermentation is a digestive process seen in monogastricherbivores, animals with a simple, single-chambered stomach.

Examples of hind gut fermentors include Proboscidea and large odd-toed ungulates such as horses and rhinos, as well as small animals such as rodents, rabbits and koalas. In contrast, fore gut fermentation is the form of cellulose digestion seen in ruminants such as cattle which have a four-chambered stomach, as well as in sloths, Acropolis, some monkeys, and one bird, the hatpin.

Hindgutfermenters generally have a cecum and large intestine that are much larger and more complex than those of a fore gut or midget fermentor. Research on small cecum fermentors such as flying squirrels, rabbits and lemurs has revealed these mammals to have a GI tract about 10-13 times the length of their body.

This is due to the high intake of fiber and other hard to digest compounds that are characteristic to the diet of monogastric herbivores. Unlike in fore gut fermentors, the cecum is located after the stomach and small intestine in monogastric animals, which limits the amount of further digestion or absorption that can occur after the food is fermented.

In smaller hindgutfermenters of the orderLagomorpha (rabbits, hares, and pikes), heliotropes formed in the cecum are passed through the large intestine and subsequently reinvested to allow another opportunity to absorb nutrients. Heliotropes are surrounded by a layer of mucus which protects them from stomach acid but which does not inhibit nutrient absorption in the small intestine.

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Coprophagy is also practiced by some rodents, such as the Barbara, guinea pig and related species, and by the marsupial common ringtail possum. This process is also beneficial in allowing for restoration of the microflora population, or gut flora.

These microbes are found in the digestive organs of living creatures and can act as protective agents that strengthen the immune system. Hindgutfermenters do have the ability to expel their microflora, which is useful during the acts of hibernation, estivation and torpor.

While fore gut fermentation is generally considered more efficient, and monogastric animals cannot digest cellulose as efficiently as ruminants, hind gut fermentation allows animals to consume small amounts of low-quality forage all day long and thus survive in conditions where ruminants might not be able to obtain nutrition adequate for their needs. Hindgutfermenters are able to extract more nutrition out of small quantities of feed.

The large hind-gut fermentors are bulk feeders: they ingest large quantities of low-nutrient food, which they process more rapidly than would be possible for a similarly sized fore gut fermentor. The main food in that category is grass, and grassland grazers move over long distances to take advantage of the growth phases of grass in different regions.

The ability to process food more rapidly than fore gut fermentors gives hindgutfermenters an advantage at very large body size, as they are able to accommodate significantly larger food intakes. The largest extant and prehistoric mega herbivores, elephants and indricotheres (a type of rhino), respectively, have been hindgutfermenters.

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Study of the rates of evolution of larger maximum body mass in different terrestrial mammalian groups has shown that the fastest growth in body mass over time occurred in hindgutfermenters (perissodactyls, rodents and proboscis). Hindgutfermenters are subdivided into two groups based on the relative size of various digestive organs in relationship to the rest of the system: colonic fermentors tend to be larger species such as horses, and cecal fermentors are smaller animals such as rabbits and rodents.

However, in spite of the terminology, colonic fermentors such as horses make extensive use of the cecum to break down cellulose. Also, colonic fermentors typically have a proportionally longer large intestine than small intestine, whereas cecal fermentors have a considerably enlarged cecum compared to the rest of the digestive tract.

In addition to mammals, several insects are also hindgutfermenters, the best studied of which are the termites, which are characterized by an enlarged “paunch” of the hind gut that also houses the bulk of the gut microbiota. Digestion of wood particles in lower termites is accomplished inside the foursomes of gut flagellates, but in the flagellate-free higher termites, this appears to be accomplished by fibre-associated bacteria.

^ a b c Animal Structure & Function Archived 2012-05-02 at the Payback Machine. ^ a b Grant, Kerri Adaptations in Herbivore Nutrition, July 30, 2010.

^ Graham, A.; Stahl, S. D.; Parr, R.; Dominguez, M. G.; Never, A. “Fore gut fermentation in the Hatpin, a Neo tropical leaf-eating bird”.

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(Source: www.hygain.com.au)

Lu, Hsiao-Pei; Rubin Wang; Shiao-Wei Huang; Chung-Yen Lin; Martin Wu; Chitchat High; Hansen You (10 September 2012). “Mutagenic analysis reveals a functional signature for biomass degradation by cecal microbiota in the leaf-eating flying squirrel (Petaurista laborious Lena)”.

“Coprophagy and selective retention of fluid digest: their role in the nutrition of the common ringtail possum, Pseudocheirus peregrines “. ^ van der Made, Jan; Grubs, René (2010).

“The maximum attainable body size of herbivorous mammals: morphophysiological constraints on fore gut, and adaptations of hind gut fermentors (PDF). (April 2004), “The Basics of Equine Nutrition”, FS 038, The Equine Science Center, Rutgers University, archived from the original on 2007-04-08, retrieved 2017-04-02 ^ Moore, B. E.; Deformity, B.

“The Gut Microbiota of Termites: Digesting the Diversity in the Light of Ecology and Evolution”. “The fibre-associated cellulolytic bacterial community in the hind gut of wood-feeding higher termites (Nasutitermes SPP.)”.

To most, this simply means the fecal matter you clean up comes packaged in nice little balls. Let’s dive into the details of hind gut fermentation so you can better understand and improve your horse’s digestive health.

hindgut fermentation vitalize
(Source: vitalizeeq.com)

In last week’s blog, you learned the digestive system is broken into the fore gut (the stomach and the small intestine) and hind gut (the cecum and the colon). Because this fiber (aka your horse’s hay) cannot be digested by the fore gut’s enzymes, it is instead sent to the hind gut and processed using the body’s symbiotic microorganisms, more commonly known as the “bugs” in the gut.

If you read last week’s blog, you know that the horse’s stomach is about the size of a football and can only hold about 2-3 gallons at one time. The practice of feeding large amounts of grain combined with this small margin for error explains why digestive upset is so prevalent in the competition horse.

Because we have disrupted the horse’s natural grazing pattern and asked him to live the competition lifestyle, we must now work to proactively control our management programs. When your horse is stressed, he goes into “fight or flight” mode, otherwise known as stimulating the sympathetic nervous system.

In this situation the body will inhibit digestion and prioritize organs like the heart, since it is more vital if, for example, the horse needed to outrun a lion. Our goal is to keep digestion running smoothly at all times, so reducing stimulating stressors is key to a happy animal.

By incorporating a research-backed supplement to your program, like Vitalize products, you can assist your horse in keeping a balanced gut. These proactive management practices mentioned above paired with Vitalize products, which actively work to keep the “bugs” in the gut in check, create the perfect recipe for #agoodgutfeeling.

ruminant digestive hindgut system non ruminants fermenters horse cecum intestine stomach colon ppt esophagus rectum powerpoint presentation duodenum slideserve
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Certain other herbivores have also adopted this “caudal fermentation” lifestyle, most notably rabbits and rodents. However, the equine large intestine is massive and anatomically complex in comparison to most other animals.

The cecum and ascending colon have bands of smooth muscle (tenure) which cause these organs to form pouches called austral. Additionally, every few minutes the strong, mass movement-type contraction occurs that forces some cecal contents through the economic orifice into the ascending colon.

Within the ascending colon occurs segmentation and austral contractions that efficiently mix ingest and expose it to the mucosa for absorption of water, electrolytes and volatile fatty acids produced through fermentation. Fermentation and Physiology of the Equine Hind gut Digestive function in the stomach and small intestine of horses occurs pretty much as in any other monogastric animal.

Cellulose and related molecules pass through the small gut intact, although such plant material may be softened and swollen prior to entry into the cecum. The large intestine of horses and other hindgutfermenters is a fermentation system analogous to the lumen.

Most importantly, horses survive as herbivores because volatile fatty acids are produced in large quantities, absorbed through the cecal and colonic epithelium, and distributed for use throughout the body. The horse evolved as a grazing animal being able to roam across the countryside selecting forages that were easy to digest.

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The water is supplied by drinking and the ability of the GIT to pull fluid from the bloodstream in a continuous fashion. The cecum (known as the fermentation vat) is on average about four feet long and can hold eight to ten gallons of food and water.

The walls of the cecum have sac-like pouches (accusations) with many small ridges that are designed to slow the passage of food. Food remains in the cecum for up to seven hours, ensuring the microbes have adequate time to digest the feed material.

Therefore, it is recommended that any feed changes be made gradually to decrease the overpopulation of microbes and an increase in fermentation process leading to an excessive build up of gas and as a result, colic. The large colon is on average about 12 feet long and holds approximately 15 to 20 gallons of feed material and water.

Like the cecum, the walls of the colon are also calculated to allow the microbes adequate time to breakdown the feed material. Functions of the colon include absorption of water, electrolytes and short chain fatty acids.

On average, the process of ingesting food, the digestion of it, and the passage of waste material can take 36 to 72 hours. Complications that can arise in the hind gut of the horse are often the result of hastened feed changes, stress, and/or overzealous use of antibiotic and nonsteroidal medications to list a few.

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The large amount of naturally occurring bacteria and protozoa may experience an overgrowth during stressful times and a case of infectious diarrhea due to Salmonella or Clostridium may be the result. Due to the complexity of the equine gastrointestinal tract, small disturbances can quickly progress to life threatening emergencies.

Assure ®: A daily feed supplement formulated to support optimal digestive health including stabilization of the hind gut environment. Saccharomyces bollards: A live yeast probiotic that has been shown to be effective in the prevention and treatment of colitis.

Causes behind colonic ulcers include the use of NSAIDs (particularly But and Ban amine), acidity of the hind gut being altered (specifically by large quantities of undigested simple carbohydrates such as starches and sugars reaching the hind gut and producing lactic acid which changes the pH to a more acidic environment), stress (mental or physical, which releases corticosteroids that inhibit the specific anti-inflammatory prostaglandins), and long term daily use of omeprazole. Treatment: Common medications for hind gut ulcers include Sucralfate and Misoprositol.

Misoprositol protects mucosa by increasing mucus production and thus regulating inflammation. This means reducing hay, which by its nature of lignin fibers is harder to digest, puts more stress on the hind gut.

Access to adequate pasture can replace some frequent soaked hay cube meals. On average, a horse will need to be on the soaked cube program for at least 30 days.

hindgut horse distress horses
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Add some whole flax seed or stabilized flax for additional Omega 3’s, and some alfalfa pellets or timothy pellets for added easy to digest fiber and protein. For additional fat sources, coconut meal, or rice bran can be added in.

I like to recommend starting with cooling probiotics: the Lactobacillus family, abbreviated on labels as “L.” It is also important to include MOS (Manna Oligosaccharides) which helps to regulate the pH of the hind gut. It is particularly beneficial for horses who begin to transition off of Misoprositol because hemp seed oil continues to support the reduction of inflammation.

Horses need to eat hay or graze twenty hours per day. Any fasting time lasting longer than four hours is a recipe for increased stress.

These include Ginseng, ashwaganda, and holy basil, which have shown to reduce cortisol. Yeast probiotics are not recommended if a horse has an active hind gut ulcer or acidosis.

Horses are biologically designed to continuously consume small amounts of food, such as pasture grass, throughout the day. As an Amazon Associate, Dressage Today may earn an affiliate commission when you buy through links on our site.

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You might have noticed that you’ve been hearing the phrase hind gut health” in conversations about horses more so now than ever before. In this article, we break down the basics with help from experts Frank Andrews, DVD, Lima equine committee professor and director of the Equine Health Studies Program at Louisiana State University in Baton Rouge, Louisiana, and Christina (“Cricket”) Russell, DVD, a senior associate at Virginia Equine Imaging in The Plains, Virginia.

Remember, in addition to the information provided in this article, always be sure to consult your veterinarian about what is best for your horse as an individual. Fermentation provides the horse with energy, vitamins, minerals and amino acids.

When the horse suffers from poor hind gut health, he lacks these key dietary components. Horses are biologically designed to continuously consume small amounts of food, such as pasture grass throughout the day.

However, the modern performance horse often has a lifestyle that vastly differs from this model of continuous grazing. When inherent habits like this are disrupted, compromised or totally eliminated and improperly substituted, then the horse is immediately at risk for digestive issues, Andrews says.

Horses can experience a wide variety of hind gut health issues, ranging from diarrhea to torsion comics. However, according to Russell, the most commonly occurring hind gut health issue in the performance horse is colonic ulcers, which are the focus of this article.

equine gut intestine tract hindgut horses gi fermentation bacteria prebiotics probiotics annotated health marlin
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While surgery isn’t typically recommended diagnosing ulcers, it’s more indicative of just how hard it is to really understand to what degree a horse is affected, she explains. Russell references a study performed in 2005 by Franklin L. Pelegrín, DVD, that examined the presence of colonic ulcers in horses at crops.

Signs include a recurring lack of appetite, lethargy, intermittent fever, colic bouts, occasional edema on the belly from a loss of protein in the blood, weight loss and thin body condition. According to Russell, typical signs include a combination of loose manure and large fecal balls or, in some cases, complete diarrhea.

Weight loss, thin body condition and lack of appetite are some clinical signs of colonic ulcers. Typically, he says, these clinical signs actually relate to issues in the hind gut, which cannot be seen with an endoscope, so ultrasound examination and blood work are much more helpful.

This involves an ultrasound examination of the abdomen, with a focus on the horse’s right side in an effort to visualize the right dorsal colon. This, according to Russell, requires specialized equipment and skill on the part of the veterinarian in knowing where to look.

Because colonic ulcers are difficult to diagnose, veterinarians rely on a combination of clinical signs, ultrasound and blood work. Hind gut ulcers can also be detected through blood work, which provides information, in this case, on the horse’s protein levels.

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Typically, if a horse is suffering from hind gut ulcers, his albumin (the primary protein) concentration is low. Veterinarians also observe a horse’s hologram, a test measuring both white and red blood cell counts.

According to Andrews, veterinarians are now utilizing a test that detects serum amyloid A (SAA) proteins. The caveat to this kind of test is that an increase in SAA is nonspecific and any inflammation in the horse’s body can lead to an increase in SAA, meaning it is not a test that can differentiate stomach ulcers from hind gut ulcers on its own.

In terms of treatment measures for the hind gut, Andrews starts by reducing the amount of bulk in the horse’s diet. Instead, Andrews recommends pelleted feeds because the volume of materials in the hind gut is much smaller and less scratchy.

The colon’s job is to pull liquid from the horse’s food and absorb the nutrients back into his system and then package the waste into manure. Hay is a lot of work for the colon to digest and process and, in this case, it can scratch and cause irritation to the hind gut.

However, if colic signs continue, then having the horse evaluated by a veterinarian is indicated and it might be that the dietary change needs to be more gradual and hay could be added back to the diet. Andrews suggests the complete pellet diet for three months in order to treat colonic ulcers.

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Essentially, a complete pellet is grain and forage wrapped in one feed source. Typically, he suggests one cup of corn oil two times a day mixed with the senior or equine adult feed.

In addition to nutritional components and changes, Andrews suggests that owners take their horses off any and all nonsteroidal anti-inflammatories (NSAIDs), such as phenylbutazone (but) and Ban amine. He recognizes that, in some cases, older horses who suffer from chronic arthritis may need these medications on a prescribed maintenance dose.

His warning, however, is that these medications tend to exacerbate hind gut ulcers or may even cause the condition in the first place. Essentially, Russell says that prevention comes down to attempting to understand potential triggers and managing the horse’s lifestyle.

It is the owner’s responsibility to manage stress levels and provide the best maintenance routine and, when needed, the best treatment and preventive measures. Clinical signs of gastric ulcers can include changes in attitude, poor appetite, colic, decreased performance, decline in body condition, weight loss and lack of energy.

In order to perform the procedure, referred to as a gastrostomy, the horse must have fasted for 12 hours, with an exception given to water. According to Russell, it is vital that all areas of the stomach be looked at for any indication of ulcers, inflammation or other irritation.

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Grade 4 ulcers are large, coalescing and full thickness (with complete loss of the epithelial lining of the stomach), often with associated hemorrhage. Russell suggests feeding a low-starch/low-sugar diet; as in excess, it causes more acid in the horse’s digestive system.

A popular product, the Nibble, a slow-feeder hay net, has been found quite effective in these cases, as it prevents the horse from getting fat but still encourages him to continuously eat. Russell also encourages multiple grain meals throughout the day, as opposed to the conventional morning and evening feedings.

According to Russell, there is current thinking that suggests that gastric ulcers that occur in the pyloric region of the stomach may respond better to bisoprolol and sucralfate, but the ulcers in the squamous portion of the stomach seem to still respond well to omeprazole. Christina “Cricket” Russell, DVD, graduated from the Tufts University School of Veterinary Medicine in 2001.

Following graduation, she completed a large animal medicine and surgery internship at Texas A&M and realized her desire was to work on elite sport horses. Russell relocates to Florida every winter to support her clients and patients in Wellington and the surrounding areas.

She is a member of the International Society for Equine Loco motor Pathology and hopes to attain certification next year. In addition to her busy schedule focused on sports medicine, she enjoys spending time outdoors with her husband and daughter.

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After 20 years at the University of Tennessee College of Veterinary Medicine, he is currently Lima Equine Committee Professor and Director of the Equine Health Studies Program at Louisiana State University School of Veterinary Medicine. He was staff equestrian veterinarian for the 1996 Summer Olympics in Atlanta, Georgia, and has clinical and research interests in digestive health and nutritional and pharmacologic management of stomach and colonic ulcers in horses.

This means that horses have a simple, one compartment stomach and eat primarily fibrous vegetation or plant material. The horses unique digestive system enables them to utilize most all the nutrients found in fibrous plant material.

The small intestine is an average of 70 feet long in the adult horse, and is the main site of protein, fat and soluble carbohydrate digestion as well as vitamin and mineral absorption. The cecum and colon make up what is essentially a large fermentation vat containing numerous species of microorganisms, including bacteria, protozoa and yeast.

The lignin is resistant to bacterial fermentation, yet it plays an important role in maintaining normal gastrointestinal motility and function. IFAS are readily absorbed into the bloodstream and transported for direct energy use, or for synthesis and storage of glucose or fat.

Production of IFAS and lactic acid result in a slower energy release, compared to the quick breakdown of soluble carbohydrates in the fore gut. For this reason, continued intake of small, high-fiber meals helps to prevent large swings in blood glucose concentration (i.e. a “sugar rush”).

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Since different bacterial species are required for fermentation of different feed stuffs, a small change in the diet can alter the balance. Should a large quantity of soluble carbohydrates reach the hind gut (commonly referred to as “starch overload”), excess lactic acid and Via production occurs.

The long-stem plant sources (generally at least 1 inch in length) are important to facilitate proper gut motility and an appropriate rate of passage of digest through the intestines. To maintain effective digestive health and function, long-stem plant material, primarily from hay or pasture, should make up no less than 50% of the diet and be fed at a minimum of 1.5% of the horse’s body weight per day.

The shorter-stem, ground or pelleted plant sources of dietary fiber are often found in commercial horse feed products. The benefit of having less fermentable fiber in a horse concentrate product is to provide bulk to the diet, helping to slow intake, encourage water consumption and ultimately prevent digestive upsets.

These products provide a consistent, guaranteed nutritional analysis and are a convenient way to supplement additional fiber to the horse’s diet. A high-fiber feed can be especially beneficial for horses that travel to help minimize digestive upsets associated with changes in diet or environment.

Research reports that insufficient fiber can lead to hind gut acidosis, colic, gastric ulcers, stable vices and behavioral problems. When developing or balancing the equine diet, the quantity, quality and type of forage or other high-fiber containing horse feed should be the first consideration.

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This study compared different forage intakes using sedentary horses. Eight adult Icelandic horses were used and all horses were tested on forage intake of haulage for maintenance requirements and forage intake of haulage for maintenance requirements × 1.5.

The results show how digestibility for dry matter (DM), the fiber fractions NDF and ADF decreases when the horses are fed the higher forage intake, maintenance × 1.5 (Figure 1). Horses can increase the forage passage rate through the gastrointestinal tract and survive on poor pasture.

By increasing the passage rate they can eat much more and compensate for the lower energy content. That horses can sort out the most nutritious grass has also been shown in a study with trotters in training.

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