A Case for Vuma Strike R8
Debbie Odell MSc Agric, Pr. Sci. Nat. Consultant nutritionist for Vuma Horse Feed.
Feeding performance horses is somewhat of an art that evades perfection even after hundreds of years of concerted effort. One commonality in the feeding of performance horses is the need to supply high energy diets to facilitate the required workload. These diets are commonly grain based, with more emphasis, lately, being placed on fats and oils as an energy source. As we have discovered from bitter experience, we walk a fine line between supplying energy needs for effective training and performance, and breaking down the horse through grain overload. The digestive anatomy of the horse gives us practical clues as to how we should be feeding.
Digestive anatomy of the Horse
The horse is classified as a hind-gut fermenter. In simple terms, this means that the "front end" of the digestive system is similar to any other monogastric animal (e.g. man, chicken, pig etc), and that digestion takes place in the classical manner, by enzymatic breakdown and absorption of the end-products through the gut wall. The "back end" of the digestive system is housed within an enlarged colon and caecum, and breakdown of nutrients here is accomplished almost exclusively by microbial fermentation (similar to the processes in the rumen of a cow). The foregut (stomach and small intestine) has a small capacity (about 38% of the total) relative to the capacity of the hind gut. This would suggest that the horse is not well suited to large single meals, but rather to continuous intake of a high fibre diet. The hind gut contains a "microbial soup" - a host of different microbes which break down and utilize the substrate provided by the diet. Any feed that passes through the stomach and small intestine undigested, will be subjected to microbial fermentation in the hind gut. The end-products of the fermentation process are mainly volatile fatty acids, heat and gas.
However, horses need high energy diets in order to perform, and grains form the mainstay of such diets. The problem with high grain diets results from the disruption of the sensitive pH balance in the hind gut. The hind gut microbial population is not static, but changes depending upon the substrate provided. A diet high in carbohydrate and low in fibre will favour the microbial population with the capabilities of utilizing these substrates, to the detriment of others. The health of this microbial population is essential to the health of the horse. Sudden changes in diet will cause a radical die-off of segments of the microbial population that are not able to survive the new gut conditions. These dying microbes produce toxins which cause damage to the gut lining and may in turn enter the bloodstream, causing colic, and laminitis in acute cases.
High Grain Diets
Any excess of grain, over and above the capacity of the foregut to digest, enters the hindgut and is presented to the microbes for fermentation. The microbial population will change in order to accommodate the change in substrate. The microbes that are suited to fermentation of carbohydrate will proliferate, at the expense of others who will find the gut environment no longer suitable to their needs and will die. The end products of carbohydrate fermentation include volatile fatty acids and lactic acid, the presence of which will cause a reduction in the pH (i.e. a more acidic environment) in the hind gut, causing the gut lining to undergo degenerative changes and the hind gut to become "leaky" allowing toxins produced by the rapid die-off of microbes to enter the bloodstream.
Laminitis, Colic and Liver Function
Grain overload and resultant intestinal disease, are the most common cause of laminitis in horses. Toxins produced by the rapidly dying microbes that find access to the bloodstream through a compromised intestinal wall have been implicated in the development of laminitis. Studies in the USA have shown that over 45% of racehorses in training suffer from subclinical laminitis. Although not detectable at the trot, discomfort at the gallop where the pressure on the foot can exceed 1 ton per square inch, will reduce speed and result in "unexplained" poor performance.
In addition the lactic acid produced by fermentation of carbohydrates causes a generalized hind gut acidosis with a concomitant increase in blood lactate levels. Colic is often associated with elevated blood lactate levels. The liver of the horse will attempt to mop up the toxins entering the bloodstream, and will in the process also be compromised, contributing to elevated liver enzyme levels on blood tests.
Lighten Up!
The most classic cases of grain overload appear in horses which remain thin no matter how much is fed. The normal reaction to a horse that lightens up considerably is to "up the feed". In some cases though, the horse may not respond, or will respond by lightening up more. At this point the call to the feed manufacturer is made! The classic symptoms in these cases are soft and sour droppings, an indicator of gastric acidosis, and providing further concentrate will only exacerbate the condition. Although counter-intuitive, the correct way to deal with the condition would be to reduce the concentrates and increase the roughage portion of the diet. It is important to realize that this is a chronic condition and it is often remarkable how well these cases will respond to a period of spelling at grass.
"Tying Up"
Exertional rhabdomyolysis (ER or "tying up") is another condition commonly associated with continued feeding of high grain diets combined with a resumption of heavy workload after a short rest. In simplified terms, during short rest phases when the feeding level is maintained, glycogen is stored in the muscles. During hard work, insufficient oxygen may reach the muscles to utilize this glycogen aerobically. Anaerobic conditions will then prevail causing inflammation from cell damage and the release of cell constituents into the bloodstream. This results in elevated blood creatine kinase levels and the distinctive discolouration of the urine caused by the presence of myoglobin. The onset of ER may have other trigger factors as well, but the common denominator in most cases is the feeding of a high grain diet.
A note on Ulcers
High fibre diets necessitate thorough chewing. High concentrate diets require much less chewing than high fibre diets. It seems more than pure coincidence that horses on high concentrate diets are more prone to development of gastric ulcers. Part of the reason for this is because chewing induces saliva production - the more chewing, the more saliva. When horses chew hay, they produce twice the amount of saliva per kilogram, of dry matter than they do when they chew concentrates. This saliva accompanies the feed into the stomach when it is swallowed. Saliva is rich in buffers and these buffers help to moderate the acid response in the stomach and prevent acid build-up and thereby reduce the incidence and severity of gastric ulcers. Pelleted concentrates also appear to predispose horses towards gastric ulceration, possibly because of the necessity to grind the ingredients quite finely in order to bind the pellets, enabling them to be consumed faster with less saliva production.
Effects on Behaviour
Horses fed a high grain diet are by virtue of physical gut capacity, deprived of adequate levels of roughage. Low fibre levels in horse's diets have been associated with a number of behavioural anomalies including an increased incidence of wood chewing and coprophagy, wind-sucking, crib-biting, weaving, stall walking, variable appetite and sour attitude particularly evident at mealtimes. Certainly some of these vices may become habitual in the long term, but all potentially have their roots in the attempts to ease some of the physical and physiological distress caused by feeding high grain diets and inadequate roughage supply. Some studies suggest that horses alter their feeding habits to accommodate a high grain diet, by slowing down their consumption rate seemingly in an effort to reduce the amount of carbohydrate that reaches the hind gut where fermentation will take place. They therefore act to ameliorate a drop in hind gut pH that will result from carbohydrate fermentation, indicating a degree of nutritional wisdom.
Strategies to minimize negative effects
Diets high in grain are necessary to the supply of energy requirements to performance horses but there are strategies that can be employed to minimize the effects of grain overload in performance horses.
First and foremost one should work with the physical attributes of the horse. The capacity of the horses stomach is approximately 9 - 15 litres in total but it is rarely full as gastric emptying usually occurs when the stomach is two thirds full. Large meals will therefore increase the rate of gastric emptying, and in turn increase the rate of passage through the small intestine. It stands to reason then that a higher proportion of undigested grain will reach the hind gut for fermentation if large grain meals are fed. If meals are smaller, the rate of passage will be slower and the digestion process in the foregut will be more complete. It is a widely recommended rule of thumb that horses should be fed no more than 2 kg of grain at any one feed. If more concentrate is required rather increase the number of feeds per day than the amount of concentrate per meal. Processing of some grains will improve their digestibility in the small intestine.
Adequate roughage, usually supplied in the form of hay in performance yards, needs to be supplied. Horses should never stand without hay, including overnight. If the night allocation is finished by the morning check, then more should be supplied until there is some left over in the morning. Horses will eat periodically through the night and it is important that they have access to roughage. A period of starvation can increase the incidence of gastric ulcers, and can also affect blood results should samples be taken before a morning feed.
Feeding "to the manger" is a strategy often used, with the assumption that horses will eat what they need and leave the rest. Concentrate quantities are therefore increased gradually until the point where the horse leaves feed, and then that level becomes their daily allocation. Nutritional wisdom is sometimes overestimated and horses may over-eat concentrate at the expense of roughage, especially where roughage supply is erratic. With "old fashioned" diets which included higher quantities of fibre this method may have passed as acceptable, however most modern performance feeds are nutrient dense and contain very little fibre as their focus is on energy supply. It is most important that when feeding these diets one sticks to the manufacturers' recommendations in terms of daily allocation, and ensures intake and availability of good quality roughage at all times. It is also cheaper to feed this way, as not only is hay generally much less costly than concentrates, but the penalties paid for overfeeding concentrates in terms of veterinary fees and poor performance often go unrecognized.
Supplements
Feed supplements like Strike R8™ can be provided to help reduce the effects of high grain diets on the body. Strike R8™ contains acid buffers that modify the acid response in the stomach, helping to prevent the formation of gastric ulcers related to high gain or finely ground diets. Citrate salts help buffer blood lactate and gut specific selective anti-microbials effectively modify hind gut microbial populations, reducing the drop in hind gut pH caused by high grain diets. These products have proved highly effective in the control of acidosis induced laminitis. In addition, Strike R8™ contains vitamins, minerals and electrolytes that assist in the prevention of nutrition induced tying up.
Conclusion
We walk a fine line between optimum performance and nutritional breakdown when feeding sporting and performance horses. The art of feeding is to stay on the optimum performance side of the line. Feed management is critical to this and factors that must be addressed on a daily basis include meal times and the size of each meal, provision of sufficient roughage, physical form of feed, increased utilization of fats and oils as a feed source to reduce the carbohydrate load, balanced vitamins, minerals and trace elements, and provision of effective feed supplements.
Read more about Grain Overload and the performance horse...
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