Feeding for good gut health

by Dr Francois van Niekerk (PhD)(Agric)(Pr Sci Nat)

Considering the specialised nutritional needs of horses, a combination of scientifi c and practical skills is needed to maintain optimum feeding programmes. With the best genetics available and more scientifi c training techniques, it is essential that nutrition does not hinder maximum performance.

New developments in nutrition technology make training of horses more competitive every day. Nutrition is a specialised cornerstone in training. To ensure maximum performance, the equine athlete must be supplied with a consistent balanced feed intake at all times. The diet must supply the specific needs for protein, energy, minerals and vitamins and structured in such a way to avoid metabolic disturbances.

Anatomy of the digestive system
The gastrointestinal tract in the horse can be divided into four sections.

• Mouth: Food is chewed in the mouth, using a grinding action to reduce the particle size of the feed, to make it more digestible. This is an important process, as unchewed food might remain undigested throughout the small intestine, which may cause digestive upsets. Saliva is produced by the salivary glands, which moistens feed to facilitate swallowing. Horses have very sensitive and mobile lips, which in conjunction with the tongue and front teeth, help to locate and cut the herbage.
• Gastric stomach: Once the feed is swallowed, it passes through the oesophagus to reach the gastric stomach. The capacity of the stomach of a horse with a bodyweight of approximately 500 kg, varies between 7 to 15 litres, which is about 12,5 % of the total volume of the digestive tract. In foals the stomach volume varies between 0,5 to 1 litre. The volume of the stomach is generally relatively limited.
• Small intestine: The small intestine, consisting of the duodenum, jejunum and ileum has a capacity of 40 to 50 litres and is approximately 15 to 20 metres long in the adult horse. Within the first 10 to 20 cm of the duodenum, a duct coming from the liver and pancreas opens into the duodenum. The horse has no gall bladder. Digestion continues and absorption of nutrients into the bloodstream begins.
• Large intestine: The small intestine is followed by the large intestine made up of the caecum, large colon, small colon and rectum. The capacity of the large intestine is approximately 50 to 130 litres, depending on the age and breed of animal. The voluminous large intestine of the horse houses millions of bacteria that possess the necessary enzymes to digest dietary fibre. This process is called microbial fermentation with the volatile fatty acids propionic, butyric and acetic acids as the products.

Digestion in the mouth

Production of saliva during chewing can be as high as 45 litres per day in an adult horse. Therefore, a direct relationship exists between the amount of chewing required and volume of saliva produced. Most horses will take 10 to 20 minutes to consume a kilogram of concentrate, but 30 to 45 minutes to consume a kilogram of hay.

Saliva acts as a lubricant, but contains the starch digesting enzyme, amylase. While food is chewed, the process of starch digestion begins. The pH (acidity) in the mouth is normally neutral. No other enzymes are secreted in the mouth and the mechanical particle reduction is the most important function of digestion in this section.

Digestion in the stomach

The environment in the stomach is highly acidic. Amylase activity is inhibited in this environment. The digestion of protein starts in the stomach. Proteolytic enzymes are secreted and are activated in the acidic environment. Protein is digested with the release of amino acids, which are the building blocks of protein. No fibre, starch or fat digestion occurs in the stomach.

The small intestine

The small intestine is the main area of digestion for protein, fats and most of the soluble carbohydrates. Two supporting organs in the digestion of the small intestine, are the liver and the pancreas. The pancreas produces enzymes that digest protein, fats and carbohydrates. The bile produced by the liver promotes emulsification of fats to make it more accessible for the lipolytic enzymes. The inclusion of fat in the diet is an efficient way of increasing the energy content and density of the feed, resulting in less feed needed.

Most minerals, particularly calcium, zinc, copper, manganese, iron and magnesium are absorbed primarily from the small intestine. Phosphorus, sodium, potassium and chloride are absorbed from both the small and large intestine.
Most of the vitamins in the feed, particularly the B-complex vitamins, are absorbed from the small intestine. The remaining fibrous portion of the feed, undigested starch and protein, is passed to the caecum to be digested in the large intestine.

Hindgut fermentation

Fermentation occurs in the caecum, large and small colon. The large intestine houses millions of micro-organisms (including bacteria, yeasts and protozoa), which are the only organisms capable of producing the enzymes necessary to digest cellulose and other fibre components. The micro-organisms are dependent on the diet composition. It is therefore extremely important that all changes to the diet are made very slowly in order to allow the microbial population time to adapt (7 to 10 days is a sensible, practical time over which to introduce new feed).

Crude fibre and as much as 50% of the soluble carbohydrates in equine diets, resist hydrolytic digestion in the small intestine and are fermented in the large bowl. This process of fermentation produces the volatile fatty acids (VFA: acetic, propionic and butyric acids). VFA’s are absorbed and converted to glucose, contributing to the energy supply of the horse. The amount of energy a horse will obtain through this route, will depend on the quality of hay or forage (mostly the fibre content) and the availability of concentrates.

Anatomically the digestive tracts of all horse breeds are similar, but their ability to metabolise energy differs. The difference between pony breeds and thoroughbreds in their ability to handle high-energy diets, is reason for great concern in feeding management to avoid conditions such as acidosis, colic and laminitis. The large intestine expands in capacity from foal to yearling age to, allow digestion of more fibrous food.

Feed management

Any feeding programme should be aimed at maintaining the microbial population in the large intestine. While wild or feral horses (including zebras and donkeys) may be fully capable of maintaining nutrient intakes appropriate to their activity levels, the modern equine athlete undergoing enforced workloads, is dependent on its improved feeding programme to support its activities.

This can be achieved by a balanced dietary intake which includes hay, concentrates and grazing. The following guideline can be used to ensure that the diet is balanced:

• Ca:P ratio.
• Total protein intake.
• Enough essential amino acids.
• Energy (fibre and starch).
• Trace minerals/vitamins.
• Concentrate/roughage ratio.

The feed needed for optimum performance will vary among different horses depending on breed, weight and work intensity. Any changes in feeding should be done gradually. For example, in adult horses concentrates should not be increased by more than 200 g per day and in growing horses by not more than 250 g every two weeks.

In adult horses overloading or a sudden increase of digestible carbohydrates in the hindgut must be avoided. Horses need regular exercise that will help to improve their appetite, digestion, overall condition and general wellbeing.
Ultimately the feeding of the horse becomes the most important factor in its performance, health and to eventually generated income.

Dr Francois van Niekerk can be contacted at francois@nubalance.co.za or for further advice

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