Oats are a grain and are high in sugar and especially starch. So, high, in fact that all other grains are measured against it. The "high" is a glucose rise. I would feed an hour after a workout, so the horse can recover with it, rather than get high off it. A horse at maintenance does not need grain, but a horse in work may need the extra calories. Beet pulp should be 1/2 and 1/2 with it and the beet pulp should be more than 2lbs./day.
I tried to look up this Poulin Endurance Feed, which I couldn't find and wonder if this is an endurance horse?? Any way, I couldn't find that analysis, so don't know the NSC is. Then it takes the analysis of the oats and everything else that goes in his mouth to know if its too high. Total NSC of 10-12% would be best. Take a look at the feed bag and you'll probably find that this percentage has already been reached without the hay, pulp or oats. Watch his attitude and weight and make any changes slowly. If his workload changes, so should his diet.