You can start with your own brand by establishing own marketing company. For feed supplements, you need FSSAI registration and TIN number for starting own marketing company. You can get manufactured own brand at third party basis. Read complete third party process here
You can also resell other company’s products along with your own brands at pcd/franchise basis. You can purchase other products at net price basis and can sell to others after fixing your margin at these.
Hope above information was useful for you….