How to feed and build topline in your horse requires three things:
1. Adequate work - creating an environment where you horse is being worked in an appropriate manner where it will encourage topline and muscle development.
2. Adequate calorie intake - with energy need to develop topline, having the right calorie intake is essential to encourage this.
3. Good quality protein - Having a good quality protein is the building blocks to develop this topline. Without this quality the job of encouraging this will become a lot harder.