Information from askcrc.org; reprinted with permission of the Chicago Rabbinical Council
The pet foods recommended in the cRc Pesach Guide are not available where we live. What do we need to do to be able to use other brands on Pesach? Can we check the ingredients and just be sure to purchase before Pesach?
On Pesach, a Jewish person may not eat, own, or derive benefit from chametz which is fit for human or canine consumption, and owning chametz pet food to feed to an animal (even if the animal belongs to someone else or is ownerless) is a violation of the latter two of those restrictions. Ashkenazic Jews have a custom to not eat kitnios, but they may own and derive benefit from them (Rema 453:1 and Mishnah Berurah 453:10).
When the cRc "certifies" pet food for Pesach, it means that we visit the factory to determine which formulas are chametz-free, which relieves the consumer of that responsibility. However, if no certified pet food is available, you would have to carefully read the ingredient panel so as to determine if the product contains any chametz (and many, in fact, do).
The following are some pointers when reading the ingredient panel:
By no means do these pointers cover all of the ingredients used in pet food, and you might want to be in touch with a kashrus professional if you are unsure about any of the other ingredients in a given pet food. It is also worth noting that one is also forbidden from feeding basar b'chalav (a mixture of milk and meat) to an animal, at any point during the year. cRc approved pet foods do not contain basar b'chalav and if you are unable to obtain those pet foods you might want to consult with a Rabbi who can help you choose an appropriate pet food for year round use.