It is widely accepted that many diseases in man are the result of our modern way of life and more particularly the modern diet. Horses are no different and many equine diseases are also diet related.
This is an appropriate time of year to consider diet related disease when the risk of the most common disease, laminitis, is high.
When discussing diet it is logical to start with a description of the gastro intestinal tract (GIT) and its function. Understanding its function is fundamental to recognising the potential for serious and often fatal diseases such as colic, laminitis and less serious but still common problems such as gastric ulceration.
A good starting point is to consider what evolution has created. It has taken 55 million years for the horse to evolve from its earliest known fossil ancestor to the modern horse, however domestication is a mere 5000 years. This means that the way the GIT functions is largely unchanged in tens of thousands if not millions of years. However, the diet and feeding practices have changed significantly in modern times and is the source of many problems. Many of these changes have been made for our convenience and not necessarily for the benefit of the horse.
Horses are trickle feeding grazers which means that the GIT expects a continuous input of forage which is bulky but low in protein, carbohydrate and fat content. A natural diet is primarily fibre and contains very little of these complex ingredients.
The digestion process begins in the stomach where gastric acid starts to physically break down the diet. Stomach acid is very strong, stronger than battery acid and many times more acidic than vinegar. A common problem today is gastric ulceration (EGUS) which occurs when stomach acid attacks the sensitive lining of the stomach because there is insufficient food in the stomach to absorb the acid or there is not enough saliva to neutralise the acid. It is very important to understand that in the horse stomach acid is produced continuously but saliva is only produced in significant quantities when the horse is eating. The natural habit is to be grazing and eating for 16 to 17 hours per day which will ensure adequate amounts of saliva. Stabling, stress, work and restricted feeding times will therefore reduce saliva production and increase the risk of ulceration. Man on the other hand produces saliva continuously to assist with speaking but acid is produced mainly when we eat. The common practice of withholding food before strenuous exercise will also increase the risk of EGUS because it reduces saliva production and leaves the stomach partly empty. A horse should not undertake strenuous exercise within less than two and a half hours after a main feed but do give a small feed of a double hand full of chaff about 30 minutes before exercise.
The next stage in digestion occurs in the small intestine (SI) where proteins, carbohydrates, sugars and fats are broken down into absorbable nutrients by chemicals called enzymes released by the SI itself. The SI is short and food moves through continuously towards the large intestine (LI) even if it is not fully digested.
Digestion in the LI is very different and occurs by bacterial fermentation much like the rumen of a cow or even your septic tank. These bacteria break down fibrous substances such as cellulose which are indigestible by other areas in the GIT. The stomach and SI contents are acidic but the LI is mostly alkaline and this pH can be badly disturbed if significant quantities of food material such as sugars and starch which are found in lush grass arrive in the LI undigested. The useful LI bacteria are very sensitive to the presence of sugars and starches which can dramatically disturb the balance between good and harmful bacteria making the LI vulnerable to malfunction.
The LI comprises 65% of the whole digestive tract so the health of its bacterial populations is vital to the health of the horse. When significant numbers of bacteria die as a result of undigested foods arriving in the LI they release toxins into the circulation and can cause serious disease such as laminitis. These toxins can also affect the motility and emptying process of the LI and cause colic.
The way to avoid these GIT diseases would appear to be simple. Remember what evolution has created and feed small feeds of concentrates which can be digested fully in the time they take to passage through the SI. The bulk of the diet should be fibre fed ad lib which will ensure adequate saliva production, reduce the risk of EGUS and supply the LI with the bulk its bacteria require.
However, things are rarely as simple as we would wish. Many strains of modern grasses have been developed to feed farm stock which have much greater metabolic demands to produce milk or meat. These grasses can, in some cases, be too rich for horses which are not working hard and if owners also feed concentrates they can easily overfeed their horse. The use of bagged forage in which nutrient levels can be higher again can also lead to overfeeding. A simple rule of thumb is to feed your horse a total of two and a half percent of its body weight in food per day. If your horse is overweight and it needs to lose weight that percentage can be reduced to one and a half percent of body weight.
Feeding is as much an art as a science and if your horse has enough energy for the work he is asked to perform and he maintains condition his diet is most probably adequate. If he is overweight or gaining weight he is storing fat and must be eating more than he is utilising.
Science underpins knowledge and guides wise practice but remember the horse has not read the text book and is still a grazing animal. The old mantra of a little and often and keep things simple are as valid today as they were 100 years ago.