Most trainers seek the “magic bullet” that will give their animal the edge over other horses in a competition; feeding strategies alone will not achieve this. It is important to get the right perspective on this and to realise that you cannot feed to win but, you can feed not to lose. In other words, appropriate feeding should enable the horse to express its genetic potential in whatever activity it is involved in.
To explore this concept fully it is necessary to remind ourselves of some basic facts that relate to the horse. An average 450kg horse, not in work, will spend about 8 to 10 hours resting and about 14 to 16 hours eating forage during any 24 hour period. This eating behaviour will be associated with 40-55,000 chewing/jaw movements accompanied by the production of saliva. The horse will produce a lot of saliva (100-150 litres) during this eating phase. Fermentation takes place continuously in the horse’s large intestine because the evolved digestive strategy of the horse is post-gastric (hind gut) fermentation. So a naturally kept horse will rely mostly on the process of fermentation to provide itself with energy.
Extreme performance horses such as racehorses or endurance horses have a primary need for energy and this drives the demand for other nutrients such as protein, vitamins, minerals, etc. Any increases in energy intake must be accompanied by increased supplies of nutrients and vice versa. There are two major sources of energy for the performance horse, stored energy in the body and food energy. The former is represented by glycogen stores in the liver (90-220g) and muscle (3150-4100g) and triglyceride stores (fat) in the muscle (1400-2800g) and adipose tissues (~40kg!); all these figures relate to a 450kg horse. For the sprint horse, muscle glycogen reserves are key energy reserves as they represent “instant” energy sources; energy stored as fat is only slowly available. Food energy sources are represented by forages (slowly available energy), cereals (rapidly available energy) and dietary fats (slowly available energy). The chemical structure of the storage polysaccharide starch that is found largely in cereals is very similar to that of the structural polysaccharides, cellulose and hemicellulose, that form plant cell walls. The important difference is that the horse can digest starch in the small intestine but can only digest plant cell wall with the help of the microflora in its large intestine to produce volatile fatty acids, that are slow release sources of energy. Total digestion in the horse is equal to the sum of digestion in the small intestine and fermentation in the large intestine; the balance between these two processes will reflect the nature of the diet fed. For example, a hay-fed horse will depend almost entirely on fermentation in the large intestine whereas a racehorse in full work fed minimal amounts of hay (~2kg/day) will rely almost entirely on its small intestine to provide energy and nutrients from the food (concentrate) provided.
In the small intestine fats are emulsified by bile salts and then lipases hydrolyse the emulsion to fatty acids, triglycerides and glycerol that are subsequently absorbed. The giving of excessive amounts of oil may overwhelm this process leading to undigested oil entering the large intestine where it may coat fibre residues (cell wall material) and preventing fermentation. Amylases and glucosidases hydrolyse starch to maltose and glucose in the small intestine where they can be rapidly absorbed to provide “instant” energy and to replenish muscle glycogen reserves. Peptidases hydrolyse protein to peptides and amino acids that are also readily absorbed. In contrast, in the large intestine, cellulases produced by the bacteria ferment fibre to the volatile fatty acids, acetate, propionate and butyrate. Any starch escaping into this part of the gut is broken down by bacterial amylases to maltose/glucose and thence to lactic acid; small amounts are utilised but an excess can cause a lactic acidosis. The absence of lipase means that fat cannot be broken down in this part of the gut.
Day To Day Life
The daily life of a performance horse is so different from that of a resting horse. A racehorse may spend one hour working and be resting for 16-17 hours. Because it is fed a lot of concentrate, eating time is much reduced since it takes~1 hour to eat 1kg hay but only ~15minutes to eat 1kg concentrate! Thus, a racehorse may only eat for 7-8 hours so chewing is markedly reduced to 20-27,000 jaw movements/24 hours and, as a result, saliva production is also significantly reduced (50-75 litres). This is important because, as well as lubricating food that has to be swallowed, saliva fulfils an important buffering function in the stomach. Feeding the performance horse is a balancing act whereby provision of rapidly digestible energy sources (starch) must not exceed the digestive capacity of the horse’s small intestine that is ~20m long and can only retain food for 45-60 minutes.
Poor Feeding Effects
Problems that are due to poor feeding management include gastric ulcers, acidosis, laminitis and colic whereas an inappropriate diet can contribute to tying-up, sore shins, fractures, acidosis, laminitis, colic and nutrient imbalance. Thus, appropriate dietary management of the performance horse is critical to its success. Frequent problems that can arise due to indifferent management are as follows.
Gastric ulcers are caused by feeding high concentrate diets in infrequent, large meals, restricting forage intake and the imposition of stress. Thus it is necessary to feed concentrate little and often and provide ad libitum forage. Minimise stress and provide alfalfa at 5/6 hourly intervals; the high protein in the legume helps to buffer gastric acid.
“Tying-up syndrome” results mostly from bad management, bad feeding or, a combination of the two. Certain breed types such as the Quarter Horse seem predisposed to this condition. All animals should go through an adequate warm up procedure and be fed according to work intensity and not in anticipation of workload. It is imperative that the electrolyte content of the whole diet be properly balanced and for those horses that persistently tie-up it may be a good idea to replace some cereal in the ration with vegetable oil (soya/corn/sunflower).
Sore shins are very common amongst horses in training and can be caused by a combination of factors. These include inadequate training, a poor work surface, an imbalanced mineral supply and a low ration dietary cation/anion balance (DCAB). The mineral content of bone affects its breaking load, breaking strength and elasticity and when bone remodels, it can take two forms; osteoblastic bone rebuilding or, osteoclastic bone destruction. The latter occurs when animals begin training. Initially, there is bone demineralisation associated with degradation of bone matrix. The net result of this is that minerals are lost from the bone and excreted and bone density is reduced with an overall reduction in bone strength. Thus, it is no surprise that the highest rate of bone injury is about 50/60 days after the start of training when bone mineral density is at its lowest. After this, the bone reforms, mineral is deposited and the bone becomes stronger. Clearly bone must remodel during the training process in order to prepare for the stresses of performance but, how to prevent/reduce damage during this process? Loss of mineral is key to the loss of bone strength so it is advisable to try to increase bone mineral content prior to the onset of training. This may be achieved by feeding additional dietary calcium, phosphorus and magnesium. There are uncontrollable risk areas (individual differences in the efficiency of calcium absorption and the magnitude of endogenous losses) and controllable risk areas that we can do something about. These are regulating the quantity of forage fed, optimising the source of calcium, the overall dietary calcium content, the dietary DCAB and the supply of vitamin D. Thus, in order to reduce the risk of sore shins developing, animals should be trained carefully, allowing the bone adequate time to recover from the mechanical stress of exercise. Nutritional strategies that can be adopted to prevent bone injury include optimising DCAB (350+), feeding forage (supplies potassium, calcium, magnesium), salt (supplies sodium, chloride), trace elements (copper, manganese, zinc, silica) and allowing access to sunshine.
Many performance horses suffer from sub-clinical acidosis. In contrast, clinical acidosis that arises through excess rapidly fermentable carbohydrate (usually starch) flowing out of the small intestine (terminal ileum) into the large intestine (caecum) where it is rapidly converted to lactic acid, is more easily recognised. This is because the animal overtly suffers from colic that may be followed by laminitis and ultimately death. Mild clinical acidosis may be evidenced by generalised discomfort, anorexia (is this why horses mysteriously go off their feed?) and diarrhoea. Prevention of acidosis is achieved by regulating the supply of rapidly fermentable carbohydrate; no more than 1g starch/kg bodyweight/meal equivalent to 2.5g oats or 2g barley or 1.5g wheat/kg bodyweight/meal. Furthermore, feeding concentrates little and often together with ad libitum water and forage should ensure normal large intestinal function.
In conclusion, feeding high performance horses in any discipline is a balancing act! One must consider the animal’s behavioural needs and allow natural expression of feeding behaviour whilst at the same time meeting the animal’s physiological demand for energy. This is achieved by appropriate balancing of feed resources. It is imperative that energy-driven nutrient needs are met by ensuring an appropriate nutrient balance in the ration. Finally, one must consider the horse’s fermentation needs; a compromised fermentation system will cause the animal to underperform even if it does not become clinically ill. Minimising problems through getting the dietary balance right will allow the animal to realise its genetic potential… winning or losing then depends on the quality of the jockey and of course, the strength of the opposition!