Digestive System of the Horse

Overview of the Digestive System in Horses

Focusing on equine production and the unique digestive processes in horses, this guide provides detailed insights into the structure, function, and anatomy of the equine digestive system.

Types of Digestive Systems

Horses have a non-ruminant digestive system which is specially adapted for their herbivorous diet.This system is characterized by:

• Enzymatic Digestion: Occurs primarily in the foregut, where carbohydrates, proteins, and fats are broken down by enzymes.

• Microbial Digestion: Limited fiber digestion takes place in the hindgut, utilizing a complex community of microbes to ferment fibrous materials and convert them into volatile fatty acids (VFAs).

• As non-ruminant herbivores, horses demonstrate:

  • High rates of enzymatic digestion from the mouth to the ileum, which are critical for nutrient absorption.

  • High rates of microbial digestion that occur in the cecum and continue through the rectum, ensuring effective utilization of forage.

Digestive Tract Structure

The total length of the equine digestive tract is approximately 100 feet.The capacity of this system ranges from 40-50 gallons.

Composition of the Digestive Tract:

• Stomach: Constituting less than 10% of the total digestive tract, with a limited capacity due to its role in processing smaller meals throughout the day.

• Small Intestines: Account for about 30% of the digestive system, crucial for nutrient absorption.

• Hindgut: Approximately 65% of the digestive system, vital for fiber fermentation and nutrient recovery.

Digestive System Anatomy

Key Components:

• Esophagus:

  • Length: 4.5 feet

  • Capacity: 8-17 quarts

  • Functions by moving food to the stomach through a process called peristalsis, which is a one-way muscular contraction that prevents backflow.

• Small Intestine:

  • Length: 70 feet, with a diameter of 2-4 inches.

  • Capacity: 48 quarts.

  • This is the primary site for nutrient absorption, with chyme entering from the stomach.

  • Secretions include enzymes from the pancreas (trypsin, pancreatic lipase, pancreatic amylase) that facilitate the breakdown of proteins and fats, and bile from the liver that aids in fat digestion. Note that horses lack a gallbladder, leading to continuous bile secretion into the small intestine.

• Large Colon:

  • Length: 10-12 feet

  • Capacity: 80 quarts.

  • It allows for further digestion via bacterial fermentation and is crucial for maximizing nutrient absorption from fibrous feeds, although it is vulnerable to impaction if food is not managed properly.

• Cecum:

  • Also known as the "blind gut", approximately 4 feet long with a capacity of 28-32 quarts.

  • It plays a vital role in fiber digestion, housing a diverse microbial community that ferments fibrous materials, produced volatile fatty acids that are absorbed and used as energy sources.

• Small Colon:

  • Length: 10-12 feet.

  • Primarily responsible for water reabsorption and feces formation, critical for maintaining hydration and nutrient efficiency.

• Rectum:

  • Length: 1 foot.

  • It participates in fecal matter expulsion, accommodating substantial daily fecal output — averaging 33-50 lbs, with horses defecating multiple times a day.