by Dr Shannon Lee BVSc
Weight loss is a condition that many horse owners have had to deal with at one time or another. A horse that appears thin may be suffering from weight loss due to a number of causes. However there are three common causes of weight loss in horses: malnutrition, parasitism and dental disease.
Figure 1. Horse showing visible signs of weight loss
If a horse is suffering from malnutrition then the number of calories it is consuming is less than the number it is using, it may also suffer from an incorrectly balanced diet. Causes of this include feeding poor quality feed, supplying inadequate amounts of feed or the horse maybe missing out on feed due to competition at feeding time.
Parasites can rob your horse of much needed nutrition as the parasites consume the nutrients or cause inflammation of the horse's gut leading to poor absorption of nutrients across the gut wall. A targeted parasite management program involving the use of appropriate dewormers given at the correct dose, combined with pasture management and fecal egg counts should minimise the impact parasites are having on your horses.
Dental problems can decrease your horses FCR or Food Conversion Ratio this is a measure of how efficient your horse is at converting feed into energy. The first two steps in digestion are prehension or picking up the feed and mastication or chewing. Any change in the efficiency of these two steps has a direct effect on the efficiency of the rest of the digestive process, as the rest of the digestive tract is only as efficient as these two steps. In severe cases loose, fractured or infected teeth can cause a horse to stop eating all together.
There are many other causes of weight loss in the horse, however the three covered above are the most common and should always be addressed when assessing a horse for weight loss. Other causes of weight loss can include but are not limited to tumours, disease of major organs such as the kidneys or liver, issues affecting hormone levels, inflammation of the intestine, chronic infection and stomach ulcers.
A useful tool in evaluating and reassessing weight loss in horses in to use a body condition scoring system. There are two main systems used one system grades horses from 1 - 5 with 1 being very poor condition and 5 being obese the other system grades horses from 1-9. The key difference between the two systems is the greater degree of accuracy of the 1-9 system.
Another tool that can help is the use of weight tapes although bear in mind that these are not always very accurate, alternatively if you are lucky you may live in an area where you vet or racetrack have digital scales you can use to weigh your horse more accurately.
Figure 2. Horse after treatment, showing healthy weight
While we are discussing weight loss in horses we should also talk about the dangers of a horse being too heavy. The same risks posed to people by being obese apply to our horses as well as a few of their own. Overweight horses have increased pressure on their joints and vital organs and are at risk of metabolic syndrome, which has been identified as a cause of laminitis (inflammation of the sensitive structures connecting the hoof wall to the pedal bone).
Overweight horses need a decreased calorie intake often combined with an increase in exercise.