Leave the food alone and concentrate on the giardia. It can be TOUGH to cure and you could go through several rounds of Panacur, weeks on, weeks off, weeks on weeks off, before it's out. And his system will always be somewhat susceptible, and in times of stress you could see flare ups again. Metronidazole is kind of like an antibiotic Pepto pill. It really won't do much for giardia at all.