Maintaining Gut Health
Professor Jo-Anne Murray
PhD, MSc, PgDip, BSc (Hons), BHSII, RNutr, PFHEA University of Glasgow Veterinary School
As I have discussed previously, your horse’s gut plays such an important role in maintaining health and wellbeing. The gastrointestinal tract works hard to digest feedstuffs, make essential nutrients that the horse can’t produce on its own, protecting your horse from disease and even shaping the behaviour of your horse. Thus, it is vital to maintain gut health and to ensure you are managing your horse in a way that promotes gut health it is important to understand the anatomy and physiology of the equine gastrointestinal tract.
Overview of the gastrointestinal tract
The horse is classified anatomically as a non-ruminant herbivore and has a digestive tract that consists of three functional regions; the stomach and the small intestine, collectively termed the foregut, and the large intestine, often referred to as the hindgut. The first section, the foregut, is similar to the pre-caecal digestive system of a monogastric animal, such as the dog, man or pig. The second section, the hindgut, is more like the rumen of a cow. The stomach of the horse contributes only eight percent to the total digestive tract weight, with a capacity of approximately eight litres in a mature 500 kg horse. The small intestine is comprised of three functional regions: the duodenum, the jejunum and the ileum, which together account for around 30 % of the total tract mass and 75% of its total length (approximately 21-25 m in a 500 kg horse). The large intestine consists of the caecum and the large (ascending) and small (descending) colons. It is the major contributor to gastrointestinal tract volume (60 %: 15 caecum, 45 colon), and is proportionally the largest hindgut of any domestic animal. The hindgut of the horse is anatomically specialised to accommodate micro-organisms capable of degrading and fermenting the structural polysaccharides (fibrous fraction) of plants.
The digestive process begins in the mouth. The incisor teeth (n=12) bite the vegetation selected by the upper lip. The pre-molar (n=12) and molar teeth (n=12) then grind the food to facilitate a reduction in particle size, whilst mixing it with saliva secreted as a direct response to chewing. Saliva appears to have little or no digestive enzyme activity in the horse, unlike many other species. However, its mucous content allows it to act as a lubricant for the passage of the feed bolus down the oesophagus into the stomach, via a process known as peristalsis, and its inorganic salt content enables it to act as a buffer to the acidic conditions present in the stomach. Chewing is such an important aspect of digestion as a) the reduction in feed particle size improves the digestibility of the nutrient in the feed and b) horses only produce saliva as a direct result of chewing and therefore if the horse is not chewing then no saliva is being produced, which can impact on the health of your horse’s stomach.