ANTIOXIDANTS are becoming increasingly important in the diet of the horse. They mop up or prevent the formation of free radicals but what are free radicals and how do they cause damage in the horse’s body? Is it possible to prevent this damage from getting out of control?

Free radicals
In all living things, including the horse, oxidation is a very important process and an essential part of normal metabolism. 
It is this process which breaks nutrients down to be used by the body for energy, growth and repair. 
During the oxidation process free radicals are formed and these free radicals cause damage within the cells of the body. 
The main danger comes from damage done when they react with important cell components such as cell membranes or DNA. 
Environmental factors can also produce free radicals; pollution, radiation (sunshine), herbicides and mental and physical stress. 
To prevent free radical damage the horse’s body produces its own antioxidants, which under normal circumstances can handle any free radical produced. 
It is only when these antioxidants are unavailable, or if free radical damage becomes excessive, that serious damage can occur and this is when the antioxidants obtained from the horses’ feed become all important. 

Self defence
Antioxidants bind with the free radicals before they can cause any damage, transforming them into non-damaging compounds and repairing cellular damage. 
The principle antioxidants, and the ones which most studies have been conducted on, are the vitamin group, namely Vitamin E and Vitamin C. Vitamin E is one of the most effective because it dissolves in fat. 
This is very important because by far the most significant free radical damage in the body is to cell membranes and these are made of fat. 
Damage to cell membranes can result in allergies. Vitamin C is also a powerful antioxidant but is soluble in water, which means that it gets to the whole body. Unlike humans, horses can manufacture vitamin C so supplementation is not really necessary. 
The two vitamins are very efficient at mopping up free radicals and work together in synergy to do so. Trace elements are required for antioxidants to work properly; namely selenium, copper, magnesium, zinc and manganese. 
Selenium is particularly linked to the correct functioning of vitamin E. Other important antioxidants are found in plants, fruit and herbs (flavonoids to name one group) and many of these are used in horse feeds and supplements.

Feed ingredients
The horse gets vitamin E from fresh green pasture, so horses kept on pasture during the grass growing season are likely to get plenty of vitamin E. 
The quantity reduces rapidly, however, as the grass matures and dries and obviously horses on restricted grazing will have much decreased intakes. 
Fresh, well stored hay will contain some vitamin E but the older it is the less vitamin E will be available. For stable kept horses and horses fed on old hay, supplementation of vitamin E is necessary. 
Chaffs containing alfalfa and grass will also contain some vitamin E. 
Any carrots, apples etc you feed to your horse will also contain antioxidants. Many horse feeds now contain natural plant antioxidants which mean that Vitamin E levels don’t need to be quite so high.

Antioxidant levels
Purchased compound feeds (nuts or coarse mixes) will provide the horse with more than adequate vitamins and trace elements including the all important antioxidants, vitamin E and selenium. 
This is also true for feed balancers and general purpose vitamin and trace element supplements. This will, of course, only be the case if they are fed at recommended levels. 
Out of date feeds will contain little or no vitamin E as it does not store well so make sure that you keep an eye on the shelf life of products you buy. 
Extra antioxidant support will be required under certain circumstances. Generally speaking, the requirement for extra energy or extra immune response will increase antioxidant requirements due to the increased oxidation processes that take place to produce the energy. 
Growing horses, pregnant or lactating mares, veterans and horses recovering from injury and disease are all likely to benefit from antioxidant support. 
Ongoing research into the antioxidant requirements of performance horses indicates that it is likely that extra vitamin E is beneficial to aid recovery and help prevent muscle damage. 
Vitamin E in synergy with other antioxidants has also shown to be beneficial to those suffering from respiratory problems. The jury is still out but the anecdotal evidence is strongly supportive of the use of antioxidants in performance animals. 

Extra antioxidant supplementation can be provided in 2 ways; by moving onto a specialised feed or by topping up the existing feed regime. 
If you are feeding a specialist feed formulated for performance or stud feed etc at the recommended levels then the vitamin E and other vitamins and trace elements will be increased in line with the increased requirements. There are other powerful antioxidants available in the form of natural plant antioxidants, including flavonoids. 
These tend to be a special combination of plant and fruit based antioxidants and can be used to replace some of the Vitamin E requirement. 
Seaweed has high levels of antioxidants and as such is included in Harbro Horse and Pony Feeds along with garlic, which contains another potent antioxidant for support to the immune system and general health. 
Feeding a vitamin and trace element supplement or feed balancer along with chaff and possibly cereal may mean you will have to add your own antioxidants via a supplement if required. Antioxidant supplements are manufactured by most supplement companies and vitamin E is available to feed separately. 

A cautionary note
If high levels of oil are being fed special attention should be paid to the Vitamin E levels; current recommendations are to add an additional 100 IU of Vitamin E for every 100ml of added oil. Care must be taken, however, as most Vitamin E supplements that can be purchased also contain selenium as it is required for Vitamin E to function correctly. 
Selenium can become toxic at relatively low levels and if you are already feeding a feed balancer and/or a compound feed your horse’s selenium levels will be near the maximum tolerable level already. 
If you are concerned try to find a Vitamin E or antioxidant supplement which doesn’t contain selenium. Or alternatively contact a nutritionist to ask them to calculate if you are feeding too much or too little selenium. 
A very quick blood test will let you know if your horse is deficient or otherwise in selenium (the soil in the North East of Scotland is low in selenium, so may be worth checking plasma levels). 
Increased energy requirements due to hard exercise, breeding or growth and a compromised immune system will increase the need for antioxidant supplementation. 
This can be achieved by supplementation or by swapping to a specialist feed, which will be fully balanced, alleviating any concerns of toxicity or deficiencies. 
Antioxidants are very important to help the horse to protect itself against free radicals produced by normal metabolic processes (oxidation).