The national initiative was launched by the charity earlier this year to tackle the increasing problem of equine obesity.
"It's important to remember your weight management regime in the winter as well as in the summer," says Rosie Mogford, equine welfare education officer for The Blue Cross.
"Wild horses naturally lose weight in the winter but domesticated horses can do the opposite, often through the overuse of rugs, stabling and hard feed. By managing the natural process of weight loss in the winter, there will be less need to restrict feed and grazing come spring - making for a happier horse."
The Blue Cross suggests the following ideas to help keep horses and ponies in good shape over winter:
"When snow or frost cover the grass, alternative sources of fibre are required. For good doers, straw based fibre feeds are ideal as they don't contain too many additional calories.
"In addition to fibre, vitamins and minerals are required to help keep your horse or pony healthy. These can be supplied without having to significantly increase energy intake by using a low sugar lick, broad spectrum vitamin and mineral supplement or a balancer. "
The Blue Cross Fat Horse Slim campaign was launched earlier this year when the charity revealed that 40% of all horses and ponies taken in by its equine centres last year were overweight. It is backed by several leading riders, including Blenheim competitors Mary King and William Fox-Pitt.
A Fat Horse Slim weight management pack, sponsored by Dengie, provides advice on how to condition score your horse and how to manage weight loss safely and effectively at all times of year. It includes a 28-page Blue Cross guide; a Shires weigh tape; calculator; body condition score guide; wall chart for recording weight changes over time; and vouchers for free and discounted Shires and Dengie products.
The pack is available to purchase on The Blue Cross stand 54, opposite the Blenheim arena, at the special show price of £5 (usually £8). Proceeds from the packs will support the The Blue Cross's work helping animals in need.