Energy requirements of a racehorse
Team Marketing | 18.10.20
It is a well-known fact that performance horses burn up a lot of energy during training and competition, but until fairly recently, energy requirements were only a rough estimate by the National Research Council. Specifically horses in light work were estimated to require 125% of their maintenance energy requirements, horses at medium work were estimated to require 150% of their maintenance requirements and horses in intense work may require 200% of their maintenance requirements. There are several obvious and unavoidable problems with this method. Firstly individual horses vary greatly, as do environments they are kept in. Cold weather, parasites, age, body weight and many other factors can affect feed efficiency and thus energy requirements. Secondly, individual opinions of what is considered hard work can vary greatly - what a show rider considers hard work may be considered an easy week for many endurance riders. Several years ago a much more specific formula was published by Dr Joe Pagan and Dr Harold Hinz in the proceedings of the Equine Nutrition and Physiology Society. Although the data collected for this research was done from the flat, it still showed to be the most accurate field method for estimating energy expenditure during exercise to date. It is interesting to calculate the number of joules needed for an average horse to cover 80km. A horse weighing 410kg carrying a 75 kg rider and covering the 80km in 6 hours burns up around 75.5 MJ of energy. The same horse, which carries a 95kg rider and completes the coarse in 4 hours, burns up to 110 MJ (That's equivalent to around 3.5kg of oats extra for the trip). A 450kg thoroughbred would burn around 19 MJ in just 2 minutes for a mile race. That's pretty impressive when it gets most of it s energy from glucose when an endurance horse gets a majority of its energy from fat body stores which is in greater supply. Since feed efficiency is only around 60% efficient for a typical ration (that means only 60 of the energy actually gets utilized in energy production, the rest is burnt in metabolism or lost as heat, etc). That means that you would have to feed the above endurance horses 126MJ and 180MJ, respectively to make up the energy burnt during an 80km ride. If you were feeding oats to replace that energy you would have to feed around 12 -18kg of oats in addition to the horse's maintenance ration, which for a normal horse is around 55MJ. Obviously you can't replace all that energy in one meal, but using this information you can plan a nutritional program to maintain your horses health, condition and performance levels. For the number crunchers the formula is Y = e 3.20+0.0065x where x is the speed per minute and Y equals the amount of calories spent per kg per minute. To use this formula you will need to use a scientific calculator. That's the one with all the buttons up top. Firstly you have to work out your average speed (X). Its doesn't really matter if you change your speed a lot because it will work out the same. Work out how many meters you travelled (1km =1000m) and divide the amount of meters you travelled by the number of minutes it took you to complete the ride. For example: If a 80km (80,000m) ride takes you 6 hours (360minutes) to complete. 80,000m divided by 360 minutes equals 222.22m per minute. Multiply this number (X) 222.22 by 0.0065 and add 3.20. This number will equal 4.644. Write this number down. Now you should find the inverse function for the natural log. The primary function on the calculator button will say 'LN" and the 2nd function key will have an "e" with an "x" superscript. Take the number you have just wrote down (4.644), push the 2nd function key (or the inverse button) and then the "LN" key to get the inverse function. For our example you will get the number 103.96. This is the number of calories your horse is burning per minute, per kilogram of weight moving along the track. This is the value of "Y". Write this number down. To calculate the total expenditure of your horse for the race you need to know how many kilograms you, your horse and your gear weights. For example your horse may weigh 425kg, you and your gear may weigh 75kg. That's a total of 500kg of weight your horse has to move. Now take the total number of kilograms (500) and multiply it by "Y" (103.96). Then calculate that number by the number of minutes (360) you were riding. The answer for our example should be 18,712,800 calories. To convert this number into something easier to handle divide the number by 1,000,000. This will result in the number being expressed as 18.712 Mcals or since Australians usually use the metric system, that's around 78.3 MJ of energy. 1 cal equals 4.185 joules). Since feeding efficiency is only around 60%, divide the above number (78.3MJ) by 0.60, which equals 130.5MJ of extra energy burned during this ride. To gain an appreciation of this that's around 15 cups of oil or 10kg of oats of extra energy your horse will require to finish the event. Obviously you will not be able to feed your horse all of this extra energy in one day. So you will have to be mindful that in the weeks leading up to a long race such as this that you feed extra feed to your horse so that he has enough energy to compete at optimal levels for the event. This formula give a good estimate to the amount of energy your horse will exert. The amount of energy exerted will vary depending of the temperature, terrain, skill of the ride, the type of feed and its digestive efficiency.