Sounds like the Science diet may be too high fiber for him. I had a similar experience with my terrier when I decided to try him on Natural Balance kibble (one of the high fiber ones).
At first it agreed with him but after about 2 weeks he started having loose stools, I only tolerated it for one day, threw away the Natural Balance and put him back on Zignature.
Problem solved.
Ps: Don’t be surprised if he doesn’t have a bowel movement for a day or two. It takes a few days for the system to get back to normal.
