Horses have developed a symbiotic relationship with hundreds of different species of micro-organisms which help break down components of the feed, thereby making the food available to both the "bug" and the host animal. A typical horse's digestive system harbours more than 500 distinct species of micro-organisms. They are, however, extremely sensitive to changes in pH and any abrupt change in diet will cause a population shift which can lead to disaster.

Generally, the types of bacteria proliferating on very high grain diets cause a lower than normal pH in the gut, which can lead to all sorts of secondary problems. Research and practical experience show that the healthiest horses are those treated as horses should be treated – fed quality fibre on a continual basis and correctly formulated concentrates which do not rely heavily on energy from grains.

Micro-organisms and the modern horse
In most cases, the modern horse cannot graze all day, and often the expected workload requires more nutrients than what is actually available from the roughage alone – and this is where problems begin. The daily energy requirements for hardworking horses are about double the requirements of a horse not in work. There is thus clearly a direct conflict between how the horse has evolved on the one hand, and modern ways of keeping horses coupled with what is demanded from them.

Non-working adult horses can be maintained on high quality forages without grain supplementation. However, the horse's requirement for energy increases 25%, 50% and 100% as its work level increases from light, to moderate, to heavy.

What about colic?
In the mature horse, the exit and entrance to the cecum are separated by only about 5cm. This creates a certain amount of difficulty due to the two-way movement of feed in this region. As a result, the cecum can be a site of colic, which may develop when a horse is shifted from a poor quality ration to one which is rapidly digested.

Bacteria which are best at digesting high fibre type diets, will be replaced with a population of bacteria which are more suited to convert high quality and easily digested fibre to soluble products. As easily digested hay enters the cecum, microbial populations flourish and there is an increase in fermentation rate.
The coarse roughage can cause a relative occlusion at the exit of the cecum and could result in gas accumulation and the pain associated with colic. This is the principle behind the recommendation that "a horse should be shifted from one type of feed to another over a period of one to two weeks."
Badly formulated, high grain rations will certainly cause undesirable population shifts and very low quality roughages could further predispose the horse to impactions.

And laminitis?
The cause of a large percentage of equine laminitis is poor digestion. While various factors can predispose horses to this condition, the most common cause appears to be a carbohydrate overload in the small intestine.

Carbohydrates escaping digestion in the foregut move on to the hindgut where a proliferation of lactic acid bacteria and an increase in acidity resulting from fermentation in the cecum occur. This increased acidity kills the beneficial fibre fermenting bacteria and causes irritation of the gut lining where endotoxins are absorbed into the bloodstream, resulting in impaired circulation, especially in the hooves.

Pitfalls and recommendations
• Do not overfeed grain! Excess grain not digested in the small intestine, passes into the large intestine and ferments extremely well. Excess fermentation causes changes in the pH and excess gas, which dramatically increases the potential for colic or laminitis. Choose a concentrate specifically formulated with lower grain content and which obtains the required energy levels from super fibres and oils.
• Make sure clean, fresh water is available at all times at the right temperature.
• Dirty water or water that is too cold in the winter or too hot in the summer, will inhibit consumption. The large intestine also serves as a large reservoir, providing a reserve of electrolytes and excess water essential for cooling the body. Lack of water will reduce the water required in the reservoir and inhibit fermentation and material flow.
• Fibre quality and quantity are primary in any horse's diet. Poor hay quality will cause loss of weight and hay bellies. Lack of quantity will cause an imbalance between grain and fibre, thus increasing the potential of colic or laminitis. Another good rule of thumb is to make sure that the fibre portion of the diet is always a minimum of 50% of the total diet or a minimum of 1% of body weight.
• Reduce rapid fibre changes. Everyone knows not to change the type of concentrate overnight, but the same rule should apply to fibre. Ease into a new cutting or delivery of hay and gradually introduce the horse to new spring or different pastures.
• Allow adequate turnout time where possible. The same research that has proven that rapid fibre changes are a leading cause of colic, also indicates that lack of proper turnout is also a leading cause.

Early warning signs
Some indications that the hindgut is not functioning very well and that alternative feeding options need to be considered for improved digestive health are:
• A hay belly which indicates that poor quality forage is being provided. The large intestine will retain poor quality forages longer, while trying to get as much nutrition as possible. This will stretch the large intestine causing the hay belly appearance. Good quality forage will shrink the hindgut back to normal size.
• Cow flops rather than road apples. Manure that more often resembles cow manure, indicates that fermentation in the large intestine is not functioning optimally. This often occurs with rapid fibre changes, excess grain, or just poor intestinal health often associated with age. Do not overlook the potential for illnesses requiring the attention of a vet.
• Poor hair coat or hoof condition. Typically, these would accompany one or both of the problems listed above.

Outside influences such as pasture availability, energy and work requirements, owner life styles, etc. have an influence on the digestive system of the horse that is not always ­positive.
Even with the more demanding and "unnatural" lifestyle which horses ­often have to endure, there is no reason for them to suffer from poor digestive health. Improved high fibre feeds are on the forefront of equine nutrition and are readily available. Ensure, however, that you know what constitutes the feed you buy or discuss your horse's diet with an equine nutritionist.
(Read more about digestive health by visiting www.equusfeeds.co.za and clicking on Articles of Interest)