whats the best way to get your horse to gain weight?

[countrycowgirl]

i have a three year old quarter horse that im training to run barrels. everysince i got him i never really could get him to gain weight and when i did i couldn't get him to keep it on? any suggestions would be great help thanks :D :confused:

[countrycowgirl]

sorry i typed that one part wrong i really couldn't get him to gain weight