A healthy coat comes from having a healthy horse inside and out. I would reccomend ensuring your worming programme is up to date..... second I would add a high fat/energy content feed. A few suitable feeds are soyabean meal, linseed (prepared correctly), maize or sunflower seeds. Any type of oil will have benifit. But do be careful as high fat/energy feeds can make your horse excitable. Soyabean meal seems not to heat them up to much as other feeds do. Assuming your horse is healthy on the inside it is then important to have clean skin And hair. I reccomend chlorhexidine scrub sometimes known as chlorex. It is available from your vet. Chlorhexidine is what vets often use as a pre surgery scrub, it is pink, smells a bit like bubblegum and has a consistency of thick shampoo. You can either mix it up in a bucket and sponge it on or apply like shampoo and curry comb through. As it is a bacteria/ fungus wash it will give your horse a wash similiar to washing in iodine/iovone without the disadvantages that iodine brings ie: dry coat. I find it especially good for tails/docks as while I always try to rinse it all out, if you don't manage to get it ALL out it doesn't cause itchiness like shampoos do. I NEVER use shampoo and I have prepared yearlings for all major yearling sales in australia. Saying that I have used colour enhancers/highlighters at the sales. When preparing for your show don't go mad with your coat shine, after washing a light spray on a soft dandy brush then brush your horse all over in circular motion to cover the entire hair, then brush smooth and in the direction you want the hair to lay with a body brush. Finish with a CLEAN cotton rug. You'll fing in the morning your horse will have a great shine and prob wouldn't need to reapply. Heavy oily coats look terrible. Don't put coat shine in the tail until right before the show as there is nothing worse than a heavy oily tail.