Professor Bettina Dunkel, Head of RVC Equine and Professor in Equine Internal Medicine, Emergency and Critical Care, explains why we need to understand and look after our horses’ digestive systems
The equine gastrointestinal tract is a highly complex system. While its intricate design allows horses to survive on grass alone, it can also be a major source of sometimes life-threatening disease, namely colic. This short article will introduce the main parts of the gastrointestinal system, explain their normal function and also point out where things can go wrong.
A complicated anatomy
The first part of the gastrointestinal tract is the stomach. The horse’s stomach is comparatively small, as horses are meant to spend most of their time grazing, taking in small quantities over a long period of time. Within the stomach, food is exposed to gastric acid and digestive enzymes, starting the first stage of digestion, which unlocks the nutrients from feed. From the stomach, ingesta is transported into the small intestine.
Gastric ulcers are a common problem in horses. The reasons why gastric ulcers develop are complex and not yet completely understood. However, changes in feeding patterns from continuous grazing to feeding more grain and limiting continuous access to pasture and roughage do play a role and predispose horses to ulcer formation. The small intestine of a 500kg adult horse is comprised of three sections, the duodenum, the jejunum and the ileum and is approximately 20-25 meters long in total. Here, digestion continues and small sugar and protein molecules are absorbed. Due to its length and relatively free movability within the abdomen, the small intestine can become entrapped within the abdomen or twist on itself, giving rise to colic.
These colic episodes are often severe and most of them will require surgery to either free the intestine or even resect a part if it is too compromised. From the small intestine, ingesta is emptied into the first part of the large intestine, the caecum. The caecum is a large, blind ending sack located on the right side of the horse’s abdomen and serves as a fermentation chamber where fibre is broken down with the help of the normal gut bacteria.
From the caecum, ingesta is transported into the large colon where bacterial fibre breakdown continues and the majority of the water within the ingesta is being absorbed into the blood stream. The large colon is arranged in a double-loop, crossing from the right side to the left and back again. This double-loop is freely movable and can become displaced within the abdomen causing colic. Sometimes, the colon can spontaneously return into its normal position but occasionally surgery is necessary to bring it back into the correct position.
With certain bacterial infections or parasite infestations, particularly small strongyle larvae, the colon wall can become inflamed and rather than absorbing water, fluid is secreted into the gut lumen, causing diarrhoea. The severity of diarrhoea can range from mild and self-limiting to severe and life-threatening. Horses with severe diarrhoea require immediate hospitalisation and intense treatment as they are not only losing water and electrolytes but also, absorb bacterial toxins from the lumen across the inflamed gut wall. The opposite can also occur: if a horse doesn’t drink enough, becomes dehydrated or the colon motility is disturbed, dried out, ingesta can accumulate within the lumen of the colon and become impacted. These impactions are a common cause of colic. An impaction is likely if a horse has been eating well but has not passed a normal amount of faeces.
Most impactions can be resolved relatively easily by giving fluids to the horse, usually by passing a tube into the stomach to allow direct administration of 6-8 litres of water, sometimes repeatedly, which helps to soften the ingesta and allows it to be move on into the next part, the small colon. Here, the ingesta is formed into the characteristic faecal balls which are then passed into the rectum and out. Due to its complexity, gastrointestinal problems are not uncommon and many horses will encounter some problems throughout their lifetime. It therefore helps to understand the basic function and to be prepared if difficulties arise.
Tips to minimise the risk of colic
Feed plenty of forage/fibre
Ad lib forage mops up gastric acid to reduce the risk of ulceration and also provides physical bulk in the digestive tract, to encourage gut motility and potentially reduce the risk of twists or intussusceptions that may occur if portions of the gut are empty. If, for whatever reason, your horse is not a good hay/haylage eater, you should seriously consider feeding alternatives, like Light Chaff and soaked Speedi-Beet, in separate buckets to keep your horse’s fibre intake up.
Encourage water consumption
Your horse should always have access to fresh clean drinking water but be vigilant about how much they drink, especially in extreme hot or cold temperatures. If a horse doesn’t drink enough, there is a risk of the gut contents becoming too dry and compacting to cause a blockage. Other ways to increase moisture intake include feeding soaked hay and wet/soaked feeds, like Keep Calm, as well as soaked Speedi-Beet either as an alternative fibre source or alongside the compound feed.
Ensure daily exercise
The horse is not designed for a sedentary lifestyle and physical movement is essential to keep the gut functioning and its contents moving so, if turnout is curtailed and your horse is confined to the box, even a walk round the yard is better than nothing. Change the diet with care Sometimes simply a change of forage can upset things and feeding a prebiotic, like Digest Plus, whenever change or potential stress arises, will support the microbial populations of the hindgut and help avoid upsets. Ideally, aim to make any dietary changes gradually, over a period of 10 to 14 days by slowly reducing the current forage/feed and steadily increasing the new one.
For advice on feeding horses prone to or post a colic episode, click here or, contact Baileys Nutrition Team at nutrition@baileyshorsefeeds.co.uk : 01371 85024
