Answer

By Your Horse

Lizzie Drury says:

It’s not unusual for older horses to lose weight through the summer. This is because they find it more difficult to chew and digest forage as efficiently as they did when they were younger.
Ensuring she gets adequate fibre in her diet will help to control her weight loss, and reduce the need to feed high levels of concentrate, which increase the risk of laminitis.
Most of the hay in her diet should be replaced with a short chopped fibre product that is light, or molasses free, such as Dengie Hi-Fi Lite, at a rate of up to 3.5kg a day. This can be fed in a large bucket.
I still recommend that you provide her with a small amount of hay, but it’s unlikely she’ll eat this as her first choice.
You also need to ensure that she is receiving optimum levels of vitamins and minerals, and enough quality protein to help with cell renewal, tissue and muscle repair.
To minimise the risk of laminitis, I suggest she is fed a high fibre, low sugar and starch diet. Saracen Super Fibre Pencils, at a rate of 1.5kg a day, would be ideal. These can be soaked to form a soft mash.
You could also add 10g of a yeast supplement such as Yea Sacc to her feed. The yeast works with the hindgut to ensure that there is a good healthy balance of fibre-digesting bacteria. These help the horse extract more energy out of the fibre.