Horses are non-ruminant mammals, meaning they do not have a multi-compartmented stomach. They have relatively simple guts, much like those of human beings. These herbivores have a unique digestive tract that breaks down food enzymatically.
The two sections
The horse’s stomach is divided into two sections. The first section resembles the pre-caecal digestive structure of a monogastric organism such as a dog, pig, or human. The second section is similar to the rumen of a cow. Still, the horse can neither be considered a ruminant being nor a monogastric organism. Interestingly, it cannot even be considered to be a combination of the two. This unique digestive system requires tremendous care. The horse’s weight also depends hugely on how its nutritional requirements are addressed.
Mentioned below is a detailed guide of a horse’s digestive system.
Horse feed is consumed by the mammal by firstly grasping it in the mouth using the combination of teeth, tongue, and lips. The lips are incredibly tactile when they consume their feed. Furthermore, these animals are awfully selective about what they consume. It wouldn’t be surprising to see supplements or pellets at the bottom of the feed bin.
The saliva softens the feed making it easy for the horse to swallow the food. The spit is constituted by three glands – the submaxillary, sublingual, and the parotid. They can produce up to 80 litres of saliva a day! Their saliva contains bicarbonate and small amounts of amylase. The former protects amino acids in their stomach, which is highly acidic, while the latter helps with the digestion of carbohydrates.
Male horses have 40 teeth, while females have 36. The upper jaw is wider than the bottom jaw allowing for a rather complex chewing motion. It is a sweeping action that integrates backward and forwards lateral motions as well as vertical motions. This causes the food to be ground and mixed with the saliva efficiently to kick start the digestive process.
The esophagus of a horse is a necessary muscular pipe that transports the food from the mouth to the stomach. It stands at around 1.5m in length in an adult and has low reflux capacity. Therefore, poorly chewed pieces of food can reside in the esophagus and cause the animal to choke. It then becomes imperative to maintain the teeth to ensure proper chewing of food. Adding chaff or a big stone to the feed will slow the intake rate, reducing the chances of choking.
In proportion to the size of the horse, its stomach is exceptionally small. It constitutes only 10% of the digestive system. It is, therefore, natural for the animal to eat in small quantities often. The animal’s domestication has altered this habit, and they are now expected to consume large amounts of food over 1 or 2 meals. Mainly done to adapt to our lifestyle, the procedure destabilizes a horse’s digestive system and health. This is also preferred as it reduces labour costs.
As the food enters the stomach, it is blended with pepsin and hydrochloric acid. They break down the food and aid digestion. The stomach has three primary parts; fundic, the saccus caecus, and pyloric. At the entrance of the stomach and below the esophagus is the saccus caecus portion. Here, the food is mixed with hydrochloric acid that aids in further breaking down the food. Subsequently, the food then enters the fundic region, where pepsin and stomach acid is released. This helps digestion. Finally, the food enters the pyloric region where the stomach connects with the small intestine. The food is further digested, and all fermentable Lacto-bacteria is eradicated here.
Digesta is then passed into the small intestines from the stomach. This intestine constitutes roughly 25 – 30% of the animal’s digestive tract. It can hold volumes of up to 70 litres and can reach lengths of 22 meters. The intestine is segregated into three parts; jejunum, the duodenum, and the ileum. There is only a little digestion that occurs in the stomach. Most of it happens in the intestines. The breakdown of protein, fats, etc., in the intestine is comparable to monogastric mammals. However, the activity of enzymes that perform the digestive process is much lower. The digested food is then absorbed into the intestines’ walls, and it is carried off by the bloodstream into the cells of the animal.
Commonly referred to as the hindgut, this is where the bulk of the digestion occurs. It constitutes roughly 60% of the entire stomach and has a volume of 150l. Several bacteria accomplish the digestion here. They efficiently break down undigested starches and plant fibres into simpler compounds. This can be absorbed by the intestine wall, which then passes on to the cells through the bloodstream.
The caecum is a blind sack that is over 1m in length and can contain roughly 35 litres of feed and water. Here, the food that wasn’t digested in the large intestines is broken down. The food stays for around 7 hours post, which the body absorbs the nutrients.
The bacteria here can take 3 – 4 weeks to adjust to a new diet, and this is the reason to introduce new feed to the horse slowly.
The right ventral colon, left ventral colon, and dorsal colon constitutes the large colon. It is over 3m in length and can hold up to 86 litres. The microbial digestion continues here, and the body later absorbs the nutrients.
Small colon, rectum, and anus
The small colon too is of 3m in length but has a diameter of only 10cms. The majority of the food is now digested, and the horse cannot digest the remaining. The small colon’s primary function is then to retain excess moisture and pass it onto the body. The undigested food in then is then passed through the rectum and expelled through the anus.
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