Myth or master? The weight-bearing capacity of the Icelandic horse

The amount of weight a horse can carry is often called its weight-bearing capacity. And to measure it, you can examine what percentage of its own weight the horse can carry, before it reaches the lactic acid threshold.

But reading the horse's signals of discomfort is not always easy, as horses are inherently adept at hiding both pain and feelings of discomfort. This is a consequence of its role as a prey animal, which therefore has much to lose by showing vulnerability.

The Icelandic horse is also particularly special in this context. It is a relatively small breed of horse (about 140cm tall) which, despite its small size, is largely ridden, trained and competed by adult men and women. Unique in many ways, as the norm for other horse breeds is rather that the bigger the person - the bigger the horse. Some also argue that it is particularly difficult to read Icelandic horses, a horse breed that has lived freely in the wild for an even greater part of its history.

Therefore, the research team has chosen to evaluate the weight-bearing capacity of the Icelandic horse by performing practical tests on the horses and, between each round, carrying out physiological tests, which measure how the horse's body handles the stress, in the form of measurements of heart rate (pulse), plasma lactate (when the horse receives lactic acid) and muscle enzymes (signs of muscle breakdown).

Influence of back width, conformation and muscle build

In a previous research project at the Swedish University of Agricultural Sciences and Hólar University (link to the study), it was noted that the width of the horse's back could affect its weight-bearing capacity. Therefore, Denise Söderroos is investigating, among other things, the link between the horse's exterior, i.e. different body measurements, and how weight-bearing the horses turn out to be.

The tests with Icelandic horses were carried out in three different ways to obtain the clearest possible results:

1. Weight-bearing tests during work with riders where the horses were gradually loaded with heavier and heavier weights. 16 Icelandic horses first had to carry 20% of their body weight, followed by 25%, 30% and finally 35%. For an Icelandic horse weighing 350 kg, this means that in the last test it carried 122.5 kg. During each round of the test, the horse had to run in a round pen, for a set distance and at a set speed. Blood samples were then taken to measure plasma lactate (to see if it has reached the lactic acid threshold) and signs of muscle breakdown, before the next round of testing began with the new, increasingly heavier weight.
   
   - This gave us in the research group a lot of information and made it possible to make comparisons between how much the horses could handle, and their different exterior and body measurements, says Denise Söderroos.
   
   
   
2. In the second test, the same 16 Icelandic horses were made to work without a rider, on a treadmill, with the speed of the treadmill increasing each round, as an alternative to adding more weights. As in the first work test, samples were taken between each round of testing.
   
   - ... With the help of this test, we wanted to see if there could be any correlation between the horses that could carry a lot of weight during the riding test in test 1, and those that could run at high speed here in test 2.
   
   
   
3. The third test was carried out with 20 Icelandic horses in Sweden, at the national facility Wången. Here, the research team wanted to see if it is possible to train the horse's weight-bearing ability. To find out, the horses were divided into two groups, with 10 horses trained with a rider and 10 horses trained without a rider, both under an 8-week training program.

To ensure that the horses were not harmed by the tests, a veterinarian was present to check the horses before and after the tests.

New knowledge about horses: Factors that seem to influence weight-bearing capacity

The first insight gained by the research team is that the wider the horse's chest, the better its weight-bearing capacity.

The second insight also relates to the horse's conformation; that Icelandic horses whose withers are higher than the croup seem to have better weight-bearing capacity than others.

But it also seems to be far from being as simple as a single trait alone determining the weight-bearing capacity of a horse.

Moreover, some horses never reached the lactic acid threshold despite carrying the highest measured weight, a full 35% of their own body weight. This may indicate incredible strength.

Using knowledge in equestrian life

So, how can those involved with horses apply this new knowledge in their daily lives?

We are currently analyzing the data from the third test, where two groups of Icelandic horses were trained in different ways, to retest whether the different training methods affected their weight-bearing ability.

In the future, Denise Söderroos hopes to conduct more research in the field, broadening it to include several different breeds of horses and, in the best of all possible worlds, gathering enough new knowledge to develop a method of calculating how much each individual horse can carry - perhaps based on factors such as conformation and previous training.