All depend what your horse needs, but yes supplements can helps him to keep form and helps to prevent eventual diseases.
We recommend to use FLEXADIN UCII, to protect his joints. The FLEXADIN UCII® original formula is of particular interest for horses whose joint mechanism is subject to intense effort and regular exertion. Contains patented collagen, MSM and chelated manganese, chosen to support a lasting joint health and mobility.
To support his muscular system, you can use MYO POWER to prepare the competition and support a healthy muscular development and condition.
We have also EXCELL E for a better recovery after the competition. For the loss of electrolytes after sweating we have the product ELECTROLYT 7 which is recommended after competition or intense effort.
We have a lot of products who can be used in your case. Give us more details and we'll be able to help you better.
You will find more information on http://www.equistro.com/products