I would suggest you look into becoming a veterinarian, as I don’t know diddley about animal nutrition other than the rats and chicks I worked with doing research or pet dogs and cats I have had. GI tracts differ greatly among species as well as among birds, fish, and large mammals.
Start looking at the Animal Science home page of the University of Minnesota. Perhaps you can find an email link to write a teacher there and ask about major, courses, etc.
Good luck. Sounds like a fun career.