How much should i feed my horse?

If she is an easy keeper, she might not need an added feed source. You could wait and see how she adjusts. If an increased work load is significant enough to make a notable change in her weight, you could begin with a good quality feed. Feed amount is determined by the weight of the horse and the weight of the feed as recommended on the bag. Then make adjustments as needed relative to how she responds to the beginning feed recommended amounts. She needs pasture or 24/7 free choice good hay and a salt block with fresh water, of course. Take things gradually and make adjustments as needed.