I don't think it spoils that quickly? I use it in rotation, and use it for my 2 fosters right now so it lasts longer and seems fine.
With the Orijen puppy - it is very easy to overfeed. VERY. And depending on what kind of belly a pup has - it can make it harder. I like starting puppies on a single ingredient, easy to digest food. I learned that after a foster litter that had a big problem with the Orijen - their bellies were very stressed and it was too much. Mario at Natural Pet Foods pointed out with babies, we don't feed them Thanksgiving meals, but squash only (my form of his better example!). Then slowly introduce other foods.
Ask Roxy - he is the best at the ca/ph ratio information but some foods might be Pinnacle or California Natural. Then start looking at more complicated foods. That's just thought and you don't need to follow it.
That said, of that sensitive tummy litter - my dog can eat anything now and he gets the full rotation of Nature's Logic, Acana, Orijen, whatever else catches my eye and always nice firm bouncy stool.