Feeding 'Without'
by Elizabeth Owens, Equine Nutritionist and Business Manager – Ridley AgriProducts
Fuelling exercise – During exercise a horse is reliant on body fuel stores to satisfy the requirements for muscle contraction and locomotion. There are 3 types of fuel available for horses –
- Glucose – derived from starch (grains) sugars (grains, plants and molasses) and roughages. Glucose is stored as glycogen in the liver and muscle. Approx 2% of skeletal muscle weight is glycogen. Muscle and liver glycogen stores amount to approx 3.8kgs of a 500 kg horse.
- Fatty acids – from fats and oils in the diet. Stored in fat tissue throughout the body. On average between 6-8% of a horses body weight is fat or 30 – 40 kgs for a 500 kg horse.
- Amino acids – from protein. Only a minor energy source for horses.
Which of these fuels is used depends on many factors including the type of exercise being done (high intensity, low intensity, duration etc), the type of horse, the level of fitness and the diet.
From the above you can see that we can discount protein as a major source of energy for the elite performance horse. The relative proportions of glucose (carbohydrate) and fat used depends largely on the speed and duration of the exercise. The speed and duration of the exercise determines how energy is metabolized which maybe aerobic or anaerobic.
- Aerobic – In the presence of oxygen and involves the breakdown of carbohydrate and fats in the presence of oxygen. This type of energy production provides most of the energy for trot and canter work and produces little in the way of by-products that contribute to fatigue in horses. Even for the highest intensity exercise (a 6 furlong race) aerobic metabolism provides 70 – 75% of the energy. Aerobic metabolism is 12 times more efficient than anaerobic energy metabolism.
- Anaerobic – In the absence of oxygen where glucose (from glycogen stores) is converted to lactic acid. Fat cannot be used anaerobically. This type of energy production is relatively inefficient and produces lactic acid that can contribute to fatigue. The advantage of anaerobic metabolism is that energy is generated very quickly and it is available when oxygen supply if limited i.e. during periods of intense, fast work. To a degree, a horse’s ability to run fast, and maintain that speed, is dependent on his anaerobic capacity.
At speeds greater than 600-700 m/minute, there is a shift towards anaerobic metabolism using glucose from glycogen as the fuel. A horse’s anaerobic capacity maybe increased via training and conditioning where muscle fibres employed for intense work (fast-twitch muscle fibres) become more resistant to the effects of lactic acid. Training will also improve the horse’s capacity to burn fat during low and moderate exercise and so the fit horse will use more fat and less carbohydrate, thus preserving the precious glycogen for intense efforts. This is why fat is deemed to be “glycogen sparing”. Bottom line – regardless of the intensity and duration of exercise, it is important that muscle glycogen stores are replete.
Unlike humans, it is difficult to “carbo-load” a horse since glycogen re-synthesis occurs relatively slowly in horses and may take between 24-48 to be fully replenished after hard work. This is why it is important to have the horse conditioned to a higher fat diet so that as much as glycogen as possible is “spared” during normal training.
So what does this mean??
The new format still represents prolonged, high demand work for a horse. Training needs to maximize fitness using interval work that will promote a more rapid increase in maximum aerobic capacity and to condition fast twitch muscle fibres. This requires conditioning to a higher fat diet (usually 8-10% of total diet or 800 – 1000 grams per day) and ensuring that glycogen stores are replenished daily and kept “full”.
Typical diet –
- 50% roughage – preferably grass hay and not lucerne.
- Grains - Oats do not require processing and are well digested in the small intestine meaning that the glucose is released within 4 hours of feeding. Other grains should be processed to improve digestibility – steam rolling, micronizing, extruding and/or pelleting would suffice.
- 8-10% total fat in diet – this can be achieved by using a concentrate already high in added fats and that includes high oil ingredients such as sunflower seeds, dehulled oats etc. Oil can also be added as vegetable oil (canola and sunflower combination is best) or as a high fat pellet.
Feeding during training/competition-
- Do not fed concentrates within 4 hours of competition
- Give a small grain/concentrate ration 60-90 minutes post exercise. A second grain ration can be offered 2-3 hours later
- Do not feed more than 2.5 kgs of concentrate in a single meal.
As long as the horse is not required to perform exhausting exercise for consecutive days, he should be able to maintain glycogen reserves at appropriate levels throughout periods of training and competition.
