If you want your horse to look his best many people believe that a rug is essential to stop the sun from bleaching a horse’s coat.
A dull and faded coat isn’t a good look for any horse, especially in the show ring or a competitive performance horse. Other suggestions are to keep the horse indoors during the day, paint the horse with products or use a high fat ingredient in the diet to give the horse a shiny sheen but none of these suggestions deal with the actual cause.
A diet containing the correct balance of minerals can remedy a dull faded or sunbleached coat and achieve the horse's optimum colour, according to its genes. A sun bleached or dull coat is a classic sign of mineral deficiency and the way to correct this is to put the horse on a more than adequate nutrient and mineral balanced diet.
All horses have a requirement for carbohydrates, protein, a small amount of fat, vitamins and minerals and water to stay healthy. Equine nutritionists use the ‘Nutrient Requirements of Horses’, published in 2007 by the National Research Council (NRC) to calculate needs for horses. Lactating mares have the highest needs. Growing horses require less total feed but a higher concentration of minerals compared to mature horses. The greater the body weight or workload, the greater the requirements for protein and minerals. This is why the same diet (pasture and supplementary feed) can appear to support one horse but not another if one is heavier or is on a higher workload despite both horses having a good body condition score.
The same can apply to a horse that has his workload increase. The diet may appear to support the horse quite well at the lower workload but signs of mineral deficiency may be expressed at the higher workload.
Horses most affected by sun bleaching are the darker colours like black and bays but it also affects chestnuts, buckskins and to a lesser extent greys. Some breeds are more affected than others; Friesians for example don’t bleach as much. They may be less prone to it because they genetically produce higher concentrations of very dark, protective melanin. Even if they are producing less than normal it's still more than most other horses.
It must be said that horses are individuals so two bay horses of the same weight and breed on the same diet and workload may have one exhibiting a more bleached coat. Both will still have the same mineral deficiency.
Coat pigmentation is determined by the presence, absence or relative proportions of the melanin pigments eumelanin and phaeomelanin. The melanins are relatively large, light absorbing biopolymers that occur in various similar forms. Eumelanin is either brown or black in color, but is thought to always be black in horses, whereas haeomee called melanocytes when proteins called enzymes convert the raw materials in the melanocytes (cells) into melanin pigment. Tlanin is either a reddish or yellowish rown.
Melanins are raw materials which include chemicals called indoles along with other products derived from the oxidation of an amino acid called L-tyrosine – which occurs in plants and animals including micro organisms and humans. The resulting copper dependent enzyme, tyrosinase, is then involved in melanin production. Interestingly, the lack of tyrosinase is responsible for albinism in various mammals including humans, and is related to grey hair in humans. True albinism, however, has not been identifi ed in horses.
Copper and zinc
A copper dependent enzyme called tyrosinase is responsible for the production of melanin, brownish black pigments synthesised from the amino acid tyrosine. This occurs in plants and animals including micro organisms and us. The lack of tyrosinase activity is responsible for albinism and is related to grey hair in us. Sufficient copper is needed to produce the pigment in buckskins and chestnuts and both copper and zinc are needed for black/brown/grey coats.
The purpose of the pigments is to act as a shield against light. The fading is caused by ultraviolet light oxidising the pigments. If there are less than optimal levels in the diet, the hair will be more prone to bleaching but will look normal until enough pigment has been damaged to cause the colour change.
That’s why a newly grown winter coat will appear darker but then lightens over time if the horse is copper and zinc deficient. If your horse is on a more than adequate nutrient and mineral balanced diet, there is no need for rugging or worse, being kept indoors.
Copper deficiency in other species influences coat quality and produces ‘rusting’ of dark coats, this is especially noticeable in the manes of bays and black horses. This effect in horses has not been formally proven, but horses showing red tips on dark manes of dark coats respond well to copper and zinc supplementation.
It’s not enough to simply ensure sufficient levels of copper and zinc in the diet, the balance between the two must also be considered as too much zinc in the diet has been shown to interfere with copper uptake. This is known as a secondary copper deficiency. Too much copper in the diet is believed to interfere with zinc uptake. Some people add copper sulphate to a feed; this is not good practice without taking into account the copper and zinc intake for the whole diet (pasture plus any additional feeds). The ideal ratio for copper to zinc is 1:3.
A secondary copper deficiency can be caused by other factors. High molybdenum and sulphates from grazing on affected pasture is known to interfere with copper intake. Some horse owners add inorganic yellow sulphur to their horses’ feeds. There is a very small requirement for sulphur in a horse’s diet that is easily satisfied by grass or hay, the yellow sulphur obtained from stockfeed suppliers should never be fed to a horse, it can be toxic.
A copper deficiency may be obvious with coat colour changes but can be more subtle in other parts of the body. Copper is part of many enzymes responsible for chemical reactions throughout the body. A deficiency can lead to abnormalities in bone, cartilage, tendons and ligaments and has been linked to uterine artery rupture in mares, a fatal complication of labour and with zinc, developmental bone disease in foals.
Studies have shown that a high iron intake can interfere with zinc levels causing a secondary zinc deficiency. Since pasture and hay generally have excessive levels of iron, avoid supplements that add more iron to your horse’s diet unless an iron deficiency is confirmed by your vet.
A zinc deficiency can cause a raft of issues from skin flaking and poor coat quality to poor fertility, poor hoof quality and ridging, mouth ulcers, mild anaemia (oxidative damage), suboptimal immunity and predisposition to skin infections.
It’s worth noting that anaemia due to iron deficiency is extremely rare, more likely caused by a copper deficiency as the production of the oxygen carrying haemoglobin for red blood cells requires a number of crucial copper dependent enzymes.
Of course, it’s not just copper and zinc but protein, vitamins and other minerals also need to be part of the balanced diet. Fortunately, the good news is that if your horse is on a high intake forage diet, most of the vitamins will be supplied and won’t need supplementing. An exception is vitamin E if your horse is in work.
The motto to remember is that ‘more is not better’. If there is more than adequate protein in your horse’s pasture, supplementing more is not helping your horse at all as it has to be excreted.
Keratin is an extremely strong protein and is the major component in skin, mane and tail, hooves, and teeth as is the case for us with our skin, hair and nails. Keratin is made up of a chain of amino acids with unique properties depending on the sequence; it can be inflexible and hard like hooves or soft as is the case with skin depending on the levels of the various amino acids.
Many of the amino acids that are needed for keratin are never deficient; horses can manufacture them from other amino acids. One that has to come from the diet is methionine as it cannot be manufactured by the horse. Methionine has a sulphur bond which has confused some people into thinking that sulphur should be supplemented in the diet. Feeding sulphur doesn’t create more methionine but fortunately methionine is in grass and hay and is unlikely to be deficient unless the horse is on a high grain diet with little forage.
Fats in the diet
The last consideration should be given to fat in the diet. Many people supplement vegetable oils like canola to add a shine to their horse’s coat. Without taking into account the whole diet, rectifying any deficiencies and balancing the minerals, this simply results in a shiny, mineral deficient horse. Since horses evolved on a low fat intake, less than 6%, is this in the best interests of the horse?
Fat is never deficient in the diet if grass is the predominant forage, there is no necessity to supplement more fat unless the horse is on little pasture and hay instead. Grass contains the anti inflammatory omega-3 and pro inflammatory omega-6 fatty acids in a ratio of roughly 4:1. Both are necessary for the immune system. Unfortunately all vegetable oils with the exception of linseed contains very little to no omega-3 and an abundance of omega-6 fatty acids. If your horse is mainly fed hay, he should be supplemented with linseed oil or the ground linseeds as the curing of hay destroys the fragile omega-3 fatty acids. To learn more about linseeds go to this page: Linseed, is it safe?.
The next time you visit your stockfeed supplier or saddlery, have a look at all the coat, mineral and hoof supplements, the two minerals they will all have in common is copper and zinc. Ask an independent nutritionist to help you have your pasture and/or hay tested and a mineral supplement formulated to correct any nutritional deficiencies and balance the minerals. Let your horse be the colour his genes designed him to be.
Originally published in the August - September 2010 (Vol 32 No 2) issue of Hoofbeats magazine with the title of 'Minerals and Coat Colour'.
Dr Eleanor Kellon offers equine nutrition courses
NRC Nutrient Requirements of Horses (2007)