Partitioning Digestion in Horses and Ponies

When a horse eats grass or hay or grain, the fat, protein, starch, and fiber in these ingested substances is broken down in various parts of the horse’s digestive system. Understanding feed management for horses is tied to knowing where and how the different nutrients are digested. In general, starch, protein, and fat are digested in the horse’s foregut (stomach and small intestine), while fiber is mostly digested through fermentation in the hindgut.

The only certain way to partition digestion between different parts of the digestive tract is to introduce a tube, or cannula, into each compartment and then measure the exact rate of degradation of the feeds that pass through. As early as the 1940s, cannulated ponies were used to determine the digestive processes operating within the large intestine. More recently, cannulation of the cecum and colon in the same animal have been performed to simultaneously assess feed degradation in different compartments of the horse’s large intestine.

Easy access to the rumen of both sheep and cattle has allowed ruminant nutritionists to characterize the digestive process in these animals in considerable detail. Digestion in the horse is quite different from the process in cattle and other ruminants, so research conducted on other animals is often not applicable to equines. Only recently have techniques that have been developed in pigs, cattle, and sheep been adapted for use with equids. These fundamental techniques are the in situ incubation method, in which small bags containing feed are incubated in the cecum, and the mobile nylon bag method.

The concept of enclosing feed in a container and then allowing the container to pass through the digestive tract is not new, having been tried more than 200 years ago in humans. Equine researchers now use mobile nylon bags to study nutrient disappearance throughout the digestive tract of horses and ponies. Allowing mobile nylon bags to pass through the digestive tract of the horse and then recovering them from within the tract or the feces over an extended period of time yields data that reflect a range of incubation times.

Degradation profiles obtained from in situ studies can be combined with those from mobile nylon bag studies to provide an overall impression of feed degradation in the horse. Knowledge of degradation profiles and estimates of digesta passage rate have been combined to partition digestion throughout the digestive tract of the horse. Read more about equine digestion research.