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VITAMINS
functions within the body, but are particularly important for energy generation, proper function of the nervous system, red blood cell formation, and maintenance of the digestive system and skin health. Normally in horses, B vitamins are synthesized by the population of bacteria that resides in the horse’s hindgut. These endogenous vitamins are then available for use by the horse. Clearly this provides an incentive to ensure that the bacterial balance in the hindgut is healthy and the environment hospitable. Keeping meal sizes small will help to achieve this as it reduces the amount of starch that escapes digestion in the small intestine. This is relevant as it serves to reduce the level of inhospitable acid in the hindgut as a result of starch fermentation. Live yeast supplements can also help to ameliorate some of the negative effects of high starch racing diets on the hindgut environment and microbial balance. There has been considerable interest in B vitamin supplementation in racehorses for a number of different reasons. Many of the B-group vitamins are intimately involved in the various energy generation pathways. Particularly they play an important role in the conversion of pyruvate to acetyl Co-A, which is a key stage in aerobic metabolism. Reduced or incomplete conversion of pyruvate to acetyl Co-A contributes to a build up in lactic acid in muscles, which is a significant factor in the process of fatigue. B vitamins are therefore crucial to exercise performance and it is not surprising that supplementation with them is often a feature of in-training diets.
C
URRENTLY there is no evidence to suggest that supplementation above that required to meet daily requirements is beneficial. A previous study has reported that addition of a mixed B vitamin supplement to a fortified concentrate feed had no effect on the accumulation of lactate during intense exercise. However, whilst hyper supplementation may not be beneficial, some feeds may not provide an adequate B vitamin intake, especially where microbial synthesis is reduced due to a compromised hindgut. Putting exercise performance aside, there can be other justification for B vitamin supplementation. These reputedly stimulate the appetite, which can be helpful for fussy feeders under stress. In addition, many of the ‘calming’ supplements contain sometimes quite high concentrations of B vitamins as some are said to moderate excitable behavior. There is little evidence in horses to support either of these two notions due to a lack of research undertaken in this area. Certainly suppression of appetite has been
B vitamins are believed to help calm high-str ung horses
correlated with vitamin B12 deficiency in man and folic acid supplementation has been reported to improve appetite in children. As far as the effect of B vitamin supplementation on behavior is concerned, there is again no substantiation for its use in horses, but there is clearly some involvement of certain B vitamins in mood and behavior from studies carried out in other species. Vitamin C is an additional water soluble vitamin that forms part of the body’s antioxidant defences. It is particularly important for lung and joint function and forms part of the immune defenses. Unlike the B vitamins, it is not generally found in proprietary feed, as the horses can synthesize vitamin C from glucose in the liver. It is therefore debatable whether
additional dietary vitamin C is required in normal horses with a relatively sedentary lifestyle. However, it is currently believed that the endogenous synthesis of vitamin C may not be sufficient to keep pace with an increased requirement where the production of damaging free radicals is markedly increased. This can occur with inflammation, particularly where respiratory or joint disease is present. Not all forms of vitamin C are well absorbed in horses and ironically the commonly known form (ascorbic acid) is actually very poorly absorbed. Other sources of vitamin C such as ascorbyl palmitate or calcium ascorbyl 2 monophosphate are more bioavailable. The beneficial effect of vitamin C supplementation, where respiratory disease
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