Both the hair and the hooves are largely made up of a structural protein called keratin. The specialized cells that produce keratin, such as hair follicles, are some of the most frequently dividing cells in the body, and therefore if cell division is affected due to inadequate nutrition, we often see a poor hair coat. While hooves grow more slowly (about a year to fully replace) they, too, can be a visible indication of the nutritional status of the body.
Of course, genetics plays a strong role in both hair and hoof quality ‒ as does good grooming and farrier care ‒ but poor hair and hoof growth can indicate something lacking in the diet, and thus may be improved with some dietary improvements.
The Role of Cysteine
Recall that proteins are long chains of amino acids, and the chains of keratin form long filaments that coil into helices that are held in place by sulfur-cross bridges from the amino acid cysteine. Harder keratin, such as that found in hooves, has a higher amount of cysteine in it, while hair has less. Therefore, dietary protein sources rich in cysteine are important to support hair and coat quality simply because cysteine is the major component of it.
However, cysteine is a non-essential amino acid, which means that the body can synthesize it on its own, in addition to dietary sources. The most common source of cysteine is from the breakdown of the essential amino acid methionine. Methyl-sulfonyl-methane (MSM) is a source of sulfur for horses, and has been shown to be incorporated into human hair when supplemented. Horses likely require about 5-10 g of methionine per day (an exact amount has not been established) and 15 g of sulfur per day.
There are other nutrients that play a role in other reactions involved in hair and hoof synthesis. For example, zinc is required for protein synthesis (such as keratin), and a deficiency of zinc causes hair loss (alopecia). Copper is a component of melanin synthesis, which is a dark brown/black pigment. Copper is also required to facilitate the crosslinking of collagen and elastin to form strong connective tissues. A 500-kg horse requires 100 mg of copper per day and 400 mg of zinc.
It should be noted that several other nutrients may influence the absorption of copper in particular. Excessive zinc, iron, manganese and sulfur can all decrease copper absorption, and therefore in addition to meeting minimal dietary requirements of these minerals, the ratios should also be considered. Zinc should be in a 4:1 ratio with copper, as should iron. Iron intake is often very high due to the amount of iron in the soil, and therefore forages, and is found in commercial feeds. Ideally iron is not fed at a ratio too much higher than 2-3 times the zinc. Manganese should also be fed at similar amounts to zinc. Too much sulfur, which may occur with over-supplementation or a contaminated water source, may also negatively affect copper absorption. Therefore, the zinc and copper of the diet may need to be increased (slightly) above requirements in effort to maintain these ratios depending on the amounts of iron and sulfur in the diet.
For hoof health, another important nutrient is the B vitamin, biotin. Biotin is required for cell proliferation and is normally produced in sufficient quantities by the microbial organisms in the horse’s large intestine, such that a biotin deficiency is extremely rare. Nonetheless, supplementation of biotin has been shown to improve hoof structure and strength (but not growth rate) in horses with poor hoof quality. Therefore, supplementation with ~20 mg per day of biotin may improve hoof integrity in some horses. Due to the relatively slow growth of hooves, it may take up to a year to notice any differences due to supplementation.
Another component of a shiny horse coat lies below the hair and at the skin itself. The shine of a horse’s coat comes from the hair itself, and oils produced by the skin. Supplementation with oil is a common method to improve skin health. Some oils appear to be more efficacious, and it is likely due to the content of the omega-3 fatty acids, which may also have added immune benefits.
Good sources of omega-3 fats are flaxseed oil and fish oil. Flaxseed has been shown to directly improve skin issues in dogs, and was shown to reduce the allergic response to cullicoides extract (the itch factor found in biting flies such as midges or no-see-ums). The amount to supplement isn’t well established, though 162 grams (about ½ cup) of fish oil was fed to horses in a study that found the omega-3 fatty acids were incorporated into cells. (As an aside, I witnessed the horses on that study and their hair coats were AMAZING). It should be noted that oil is also an excellent source of calories, and therefore feeding too much oil could inadvertently lead to weight gain.
There are likely some benefits to offering supplements to horses that have poor hair coats and hoof quality, particularly if nutrients may be deficient. Good quality pasture and a fortified diet would likely already provide many of these nutrients however, and care should always be taken to not overdo things. Working with a nutritionist, you can add up the nutrients in your hay/pasture, feeds and supplements and help you determine what might be lacking or how to fine-tune your horse’s diet to maximize their hair coat and hoof quality.