I don't know exactly what feed and how you mixed it, but I know when I did my mare, I put it in her grain (at the time I was using senior feed just cause it tasted the best), squirted the tube into the bucket, and then mixed it all together with water. I've heard that horses really like applesauce too, so that might be something to add some better taste. Molasses also generally works, though I would go with the minimum amount of add-ins needed to get him to eat it. My mare ate it right up without any problems. I didn't do the 5-day pack though, I just gave her her annual wormer.