When the weather begins to get cooler, it's a mistake to cut back on grooming time and to assume that your horse's nutritional needs are still being met. Just knocking off the surface dirt isn't enough. Break out your favorite curry. Get all the way down to skin level so you remove trapped dirt and dead skin cells. Once the dirt and debris are loosened, a vacuum makes removing it infinitely easier.
Regular exercise is also important. In cold weather, circulation to the skin surface is greatly decreased, and with it the production of sweat and skin oils. When you exercise the horse, circulation to the skin picks up. Benefits to the coat often are apparent in as short a period of time as a few days.
START NUTRITION NOW
Finally, there's nutrition. If your horse has any dietary shortfalls, they're likely to surface as a dull coat, often in combination with poor hooves. The end of grazing season deprives your horse of quality protein, essential fatty acids and vitamins in their optimal form. If they are not replaced in the diet, the coat and hooves will be the first to show it.
A horse's natural diet, grass, is very low in fat but does provide a constant source of the omega-3 and omega-6 fatty acids. These are the only fats that the horse can't manufacture for himself. Hays, grains and processed oils have little or no essential-fatty-acid content left in them. Even storage of whole grains leads to a reduced level of fatty acids.
To make matters worse, grass is rich in omega-3 anti-inflammatory fatty acids, which are more fragile than the omega-6 fats, and everything else we usually include in the base diet, like grain products, is high in omega-6. Adequate essential fatty acid intake is also important for hoof quality and immune function. The solution is to feed flaxseed. Flaxseed contains both omega-3 and omega-6 fatty acids, in a ratio close to grass.
Most horses have adequate total protein in their diet but could easily be lacking key amino acids because of insufficient variety of foods. Every plant, seed and grain has its own distinctive amino acid pattern. None are perfect, so feeding a variety helps guarantee all bases are covered. Feeding mixed hay is a good place to start, but if you can't feed it on a consistent basis, you can look into purchasing hay pellets or cubes to substitute for some of your regular loose hay.
Zinc is a common mineral deficiency that can manifest itself as poor quality hooves, dry skin with low resistance to infections and a dull coat. Many of the B vitamins play critical roles in hoof and skin/coat health as well. The horse's main source of B vitamins is from the teeming micro-organisms that live in a healthy digestive tract, but they are present in fresh feedstuffs as well. Estimates of B-vitamin requirements are for levels needed to avoid full-blown deficiency states but may not be the same as those required for optimal health, including hoof and skin condition. Supplementing Bs, especially biotin and pyridoxine, may help most horses that have skin/hoof problems, especially older horses or those with digestive-tract problems.
Vitamin C is another vitamin in abundant supply in fresh food and rapidly destroyed by drying and storage. Horses can make their own vitamin C when the diet is lacking it, and it's still not really clear if C supplementation is helpful. Consider adding C in winter for horses that are working hard, have lung problems of any type, or are prone to infections. C can upset the gut in large amounts, so feed no more than 5 grams/day.
Although vitamin A is critical to maintaining healthy skin, hays contain abundant vitamin A and grains/supplements are heavily fortified with it. If your hay is over six months old and you're not feeding at least 5 lbs./day of commercial grain or a high A supplement, add a few carrots a day to boost A.