There are many products out there. Not all are created with the health of your horse in mind. Simple is always better. In my practice I encourage your horse to be fed not supplemented. My standard recommendations are Perfect performance or Cool Balance feeds that is grown and produced and manufactured right here in Alberta @ Farmstead Life in Red Deer. Aloe Vera juice and Flax oil. All other supplementation should be short term. 
I also recommend Equine Choice generation 2 pre probiotics. 
Equine Choice Generation 2 & Flax Oil is available at Mattinson Farm Services & Spruce Grove Feeds. 

I have have also found the Rambo Ionic blankets and products to be very beneficial, especially for those hormonal mares. It works in a do no harm way by converting molecules to negative ions which allows natural positive charge which helps bring oxygen to the muscles. Now available at Mattinson Farm Services (780) 385-5705. 

I am am happy to book you an appointment to help find you the most efficient and cost effective natural program for your horse.