Transcript:

[0:00]

Hi everyone, welcome back to Mad Barn Academy — and if this is your first time tuning in, then welcome! We hope to earn your subscription. Today, I'm Dr. Fran Rowe, one of the veterinary nutritionists here at Mad Barn, and today's video will be part one in a two-part series on the equine digestive tract.

[0:18]

If you've watched some of our past videos that focus on various GI diseases or issues, some of this information will already be a little bit familiar. But nonetheless, I wanted to provide an overview of the gastrointestinal tract and highlight some of the most common issues seen in various areas of the equine GI tract. So, let's get started.

[0:41]

The equine digestive tract is very long and quite complicated, and there are many steps to the digestive process. To make it more manageable, I've broken this big topic into two parts: foregut and hindgut. Today we'll be focusing on the foregut.

[1:00]

Some people might say that the foregut technically only refers to the stomach and the small intestine, but I like to include the mouth and esophagus as part of the foregut because the digestive process doesn't start in the stomach — we have to start from the beginning, in the mouth. So let's do just that.

[1:22]

The digestive process starts in the mouth with mastication, or chewing. Horses use their lips and their incisor teeth to grasp feed or forage and get it into their mouth. They then use their tongue to move the feed around as they chew. Horses chew in a circular motion that effectively grinds the feed between their teeth, breaking it into smaller particles and increasing surface area, which will aid digestion later on.

[2:00]

Horses produce saliva, but equine saliva contains very few digestive enzymes. Instead, saliva acts mainly as a lubricant to help with swallowing and to buffer stomach acids once the feed bolus reaches the stomach.

[2:25]

Horses have between 36 and 44 teeth. All horses will have 12 incisor teeth and 24 cheek teeth — premolars and molars. Some horses have canines, most commonly in males, and some also have wolf teeth, which are very small vestigial premolars. Wolf teeth are often removed when the horse begins work. Because digestion starts in the mouth, keeping up with your horse’s dental health is important. Annual dental exams by a veterinarian are recommended.

[3:14]

Once the horse is ready to swallow, the tongue moves the ingesta to the back of the mouth, to the pharynx, to initiate swallowing. Swallowing is a coordinated reflex — controlled by involuntary muscle movements. Ingesta moves into the esophagus, which is essentially a muscular tube that transports feed from the mouth to the stomach. In the average-sized horse, the esophagus is about 4 to 5 feet long. It travels alongside the trachea, through the chest, and through the diaphragm before connecting to the stomach.

[4:20]

Muscle contractions that move ingesta along the esophagus — called peristalsis — are one-way only. Unlike some other species, horses cannot vomit, because they cannot produce reverse peristalsis in the esophagus. This is important for understanding certain digestive emergencies.

[4:47]

The equine stomach is located around ribs 9 to 12 on the left side of the abdomen. It’s relatively small, holding only about 2 to 4 gallons under normal circumstances. This makes sense, as horses evolved to eat small, frequent meals through foraging, rather than large, infrequent meals.

[5:35]

Because horses cannot vomit, over-distension of the stomach poses a real risk of rupture, which can be fatal. If there’s a blockage and digesta backs up into the stomach, veterinarians may pass a stomach tube to relieve gas or fluid in certain types of colic.

[6:12]

Ingesta enters the stomach from the esophagus through the cardiac sphincter — a tight valve that only opens in response to feed moving down the esophagus. Food stays in the stomach for about 3 to 4 hours before exiting into the small intestine through the pylorus. The stomach’s main functions are mixing, storage, and controlled release of feed into the small intestine, along with secreting pepsin for protein digestion.

[7:02]

The equine stomach is unique because it secretes gastric acid continuously, whether or not the horse is eating. The lower glandular region of the stomach is protected from acid, but the upper squamous portion is not. Prolonged acid exposure in this region can lead to gastric ulcers.

[7:46]

From the stomach, digesta enters the small intestine — about 70 feet long — which is bundled among the large colon. The three sections are the duodenum, jejunum, and ileum. Feed moves through the small intestine at about one foot per minute, reaching the cecum in as little as 45 minutes after a meal.

[8:53]

The small intestine digests and absorbs most starch, protein, fat, vitamins, and minerals. Enzymes from the pancreas and intestinal lining break starch into glucose, fats into fatty acids, and protein into amino acids. Most vitamin and mineral absorption also happens here.

[9:35]

Some colics involve the small intestine, often due to obstruction, twisting, entrapment, or blockage. These cases can progress rapidly and cause extreme pain, so quick veterinary attention is critical to the horse’s prognosis.

[10:22]

I’ll end today with examples of common foregut conditions. This list is not exhaustive, but I’ve included supplemental materials in the video description if you want to learn more. If you’d like a video on one or more of these conditions, put your request in the comments.

[11:00]

Here are today’s references, and thanks for listening. I hope this overview of the equine foregut was helpful. Next video will be part two, covering the hindgut, so we can put everything together. Don’t forget to like and subscribe, check out our other videos, and review the additional links in the description for more detail on the common conditions mentioned. Thanks so much — until next time.