Horses are often thought to have multiple stomachs, similar to cows. Understanding a horse’s unique digestive system is important, as its anatomy dictates specific care and feeding practices.
Understanding the Horse’s Stomach
Horses have only one stomach, making them non-ruminant herbivores. This single-chambered stomach is relatively small, holding approximately 2 to 4 gallons, or about 9% of their total digestive tract volume. Food passes through the stomach quickly, in as little as 15 minutes, or within 30 to 45 minutes for most feedstuffs.
The stomach’s primary function involves mixing food with hydrochloric acid and the enzyme pepsin, initiating the breakdown of proteins. This continuous secretion of acid is an adaptation to a horse’s natural grazing behavior, where they consume small amounts of forage throughout the day. The stomach also has two distinct regions: an upper non-glandular region that lacks acid protection, making it susceptible to ulcers, and a lower glandular region with protective lining.
The Horse’s Unique Digestive Journey
Following the stomach, food enters the small intestine, which measures approximately 50 to 70 feet in length and can hold up to 18 gallons. Here, enzymes from the pancreas and liver break down carbohydrates, fats, and proteins, allowing for the absorption of most non-fiber nutrients like starches, simple sugars, and amino acids. Horses do not have a gallbladder, so their liver continuously secretes bile to aid in fat digestion. The transit time through the small intestine is rapid, taking as little as 30 minutes to an hour.
The undigested fibrous material then moves into the hindgut, which includes the cecum, large colon, small colon, and rectum. The cecum, a large, comma-shaped sac about 4 feet long and holding 8 to 9 gallons, acts as a fermentation vat. Billions of specialized microbes, including bacteria, protozoa, and fungi, reside here, breaking down fibrous plant material that the horse’s own enzymes cannot digest. This microbial fermentation produces volatile fatty acids (VFAs), which are a significant energy source for the horse, supplying up to 70% of their daily energy needs.
From the cecum, digesta proceeds to the large colon, which can be up to 12 feet long and hold up to 22 gallons. Further microbial fermentation and water absorption occur in the large colon. The large colon’s convoluted path, with its many folds and turns, makes it susceptible to impactions. Finally, the small colon, about 10 feet long, continues to absorb water and electrolytes, forming the characteristic fecal balls before elimination. The entire digestive process, from consumption to excretion, can take between 36 to 72 hours.
Practical Implications for Horse Care
Because their stomach is relatively small and designed for continuous grazing, horses benefit from frequent, small meals rather than large, infrequent ones. Feeding large meals can overload the stomach, potentially leading to discomfort or issues like colic.
A diet primarily composed of high-quality forage, such as hay or pasture, is important to support the hindgut’s microbial population, which is responsible for fiber digestion. Consistent feeding schedules are beneficial, as horses are creatures of habit and disruptions can lead to stress and digestive upsets. Providing constant access to fresh water is necessary, as water helps move digesta through the gut and maintains hydration.
Sudden changes in diet can disrupt the delicate balance of microbes in the hindgut, potentially causing digestive problems like colic, diarrhea, or laminitis. Therefore, any dietary adjustments should be introduced gradually over several days. Ensuring proper dental care is important, as good mastication is the first step in efficient digestion.