NUTRITION
VITAMINS
I
As easy as . . .
N CONTRAST, the impact of macro ingredients such as protein, fibre, and carbohydrate can normally be clearly seen in terms of bodyweight, muscle definition, or coat condition. The characteristics or clinical signs associated with a severe state of vitamin deficiency have been clearly defined in other species, but there is less definitive information available in horses. However, severe deficiencies would rarely be found in a horse in training and excessive intake is of more concern.
Racing rations are relatively high in vitamins The basal dietary level of vitamins in a racehorse’s diet is relatively high as a significant amount of concentrate feed is usually fed. Forage, be it hay or haylage, generally has a low vitamin content in comparison and this will also reduce on storage. Beta carotene, which is sometimes known as Pro vitamin A, can be converted, albeit inefficiently, to vitamin A in the body. Grass, alfalfa and other forages are a rich source of beta carotene. Racing concentrate feeds or balancers are generally well fortified with the fat-soluble vitamins A and D but have varying levels of vitamin E. In most instances, this is enough to satisfy the minimum recommended requirement but may not be at an optimum level to support performance. Concentrate feeds may also contain a range of water-soluble B vitamins, although this is not always apparent from the bag label, as it is not a legal requirement. It is uncommon to find a significant level of vitamin C in concentrate feeds, and vitamin K may be present but not necessarily in the most bioavailable form.
20 TRAINERMAGAZINE.com ISSUE 43
Extra vitamins can often be viewed as a key ingredient to maintaining health, or optimising performance, but is this really the case? The mystique of vitamin supplements is partly upheld because it is so difficult to measure their relative benefit or worth, or indeed their necessity, unless there has been a previously deficient state. CatheRine Dunnett BSC, PhD, R.nutR
Antioxidant vitamins can be a double-edged sword Vitamin C and E both have an important antioxidant function and work collectively to support antioxidant defence. The National Research Council’s minimum requirement for vitamin E for horses in hard work is about 1000IU per day, which should easily be satisfied by an average intake of a good racing diet. However, this level may not be optimal for performance and researchers have recently suggested that 1500 to 2500 IU/day for horses in race training could be preferable. Supplementary vitamins C and E have been associated with evidence of decreased muscle damage (aspartate transaminase, or AST; creatine kinase, CK; and lactate dehydrogenase, LDH) during training. Vitamin E in feed is usually synthetic, but research suggests that natural vitamin E is more available. Water-soluble vitamin E has also recently been developed (e.g. Nano E® or Elevate®), offering a further advantage. Vitamin C is one of the most important antioxidants in lung lining fluid and joint fluid, and so it is important for maintenance of respiratory and joint health. Additionally,
ShutteRStOCK, eMMa BeRRY
vitamin C is required for the formation of collagen and has a role in soft tissue renewal and repair as well as maintaining strength of fine capillaries in the lungs. Horses do not have a strict requirement for supplementary vitamin C, as it is synthesised in the liver from glucose. However, where inflammation, respiratory, or joint disease is present, demand may overtake internal supply. Research in horses with recurrent airway obstruction (which is akin to human asthma) reports an improvement in vitamin C status and clinical symptoms with supplementation of about 20,000mg (20g) per day. Ascorbic acid is the most common form of vitamin C in feeds and supplements, but other forms such as ascorbyl 2 monophosphate or ascorbyl palmitate are more bioavailable. A particularly preparation of rosehip (Litovet®) has also been demonstrated to provide a very bioavailable natural source of vitamin C. Over-supplementing antioxidant vitamins can elicit a negative response as they may cause oxidative tissue damage by becoming pro-oxidant. However, there have been no reports of toxicity in horses for vitamins C or E.