Part one looked at understanding the basics and the digestive system explained. With the help of our expert, Dr Marion Young, we help you understand how it works and how the various feeds available affect it.
Microflora and probiotics
The hindgut is populated by microflora which release energy to the horse in the form of volatile fatty acids. Some microflora prefer forages so when they are fed too much carbohydrates, fats and proteins, the result could be one of a host of problems including acidosis, laminitis and colic, says Dr Young.
So how should we feed?
There are many clues in the physiology of the horse that guide how we should be feeding.
Teeth and mouth
The horse’s muzzle and mouth are mobile for finding and lipping at grass. The whiskers on the muzzle offer sensory information to help the horse find food. The incisors are for biting at grass, while the molars have large, flat surfaces for grinding feed. Feeding soft grains rather than fibrous roughage often leads to hooks and other dental issues in the teeth. The horse therefore needs to grind at roughage to maintain healthy teeth.
Stomach
The horse’s stomach is very small. “A 500kg Thoroughbred’s stomach will contain only about 15 litres of water if you fill it up,” says Dr Young. “Realistically, this J-shaped organ is only ever about two thirds full, and water can flow faster than feed out the top.”
In comparison to the rest of the digestive tract the stomach is definitely small, and this shows us that the horse is supposed to forage continuously throughout the day.
Intestines and hindgut
The stomach digests mostly proteins with the use of acid. There is a region in the proximal small intestine for the absorption of fats, dipeptides and amino acids. The horse has no gall bladder, which means that there is no storage of bile salts, and so the bile flows continuously through the system.
If the food passes through too quickly it will not be digested properly and will pass straight through. “It is like a train that is passing through the station but never stops to let the passengers get off,” says Dr Young. The fermentation chamber of the hindgut is called the caecum and has a capacity of 145 litres. Since this area is so large, we can tell that fibre should make up the large majority of the horse’s diet.
Roughage vs concentrate
Feeding a large amount of concentrate instead of good quality roughage means that we alter the speed at which nutrients pass through the digestive system. A large portion of carbohydrates, fats, starch and proteins don’t have time to be absorbed into the body in the foregut and therefore end up in the hindgut. They are fermented there, by-products are released and the horse can develop colic or other gastrointestinal problems.
“Our horses no longer graze on wide open fields of natural mix grasses,” says Dr Young. They might now live in paddocks and stables, but it’s important to remember that their digestive physiology is the same. “As we have increased the work and recreational demands on the horse, we have had to substitute concentrate feeds into the daily ration to match the energy requirements for work,” explains Dr Young.
To sum up, says Dr Young, the digestive physiology of the horse, from lips and teeth to rectum, is designed for the continuous ingestion of roughage. “The horse has requirements for nutrients: energy, protein, fibre, minerals,” she says. “These are provided by the feed ingested, and all raw materials have different proportions of these.”
To ensure that you are feeding the correct ratios of the different minerals, vitamins and other nutrients, you should consult a SACNASP-registered animal scientist and horse nutritionist before you use supplements or use overfeeding as a means of solving a nutritional problem.
Text: Peta Daniel
The full article appears in the April 2015 issue of HQ.