It needs to be introduced as per the directions on the back label. Start with a very little bit and increase every few days up to an amount where you can see a difference. The larger the horse the more this will be. For most horses this would probably be at least a scoop per day, for bigger horses on problem grass this could be up to 2 scoops am & pm.
Introducing slowly is very important because depending on individual requirements (size of horse, what sort of grass they are on, what the weather is doing), your horse may need to consume quite large amounts at times.
This is why there is no set dose rate. The amount your horse needs will vary with the season and the weather – as a general rule of thumb, increase until your horse is back to normal. Thereafter you will likely need less over dry spells and more when it rains. Increase the dose when it starts to rain, rather than after the rain is finished and the horse is showing signs. Be pro-active.