Pro Plan is used by probably the majority of Doberman show folks - they can't all be wrong
It is a good easily available kibble. That said, I think that there are better kibbles out there, but I personally recommend Pro Plan as a good alternative to very expensive premium kibble. If your dog does well on it, then I don't see any reason to change unless you want to.
I fed pro plan for 11 years with good results.
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Dillon's Barclay Amy CD RN WAC CGC TDInc "Velma"
CH Cha-Rish A Moment Like This RN WAC CGC "Louise"
Fitzmar's Command A Minute "Harvard" (10 pts/both majors)
http://fitzmardobermans.freeservers.com/