Hmmm..now I think of it I've heard all sorts of things about nightshade plants. You might be onto something. Worth a shot anyway.
Well, a decade (and then some) ago I worked at a pet store that carried Darford biscuits. They were pretty much in line with Nutro for quality at that time. I saw these biscuits at the specialty store here which I thought was odd (I didn't think they would qualify for a specialty store). I read the ingredients and it didn't look like anything had changed. I wasn't aware that Darford made food though, so maybe that is higher quality?
Roxy - Feb 2005 - 75 lb American Staffordshire Bull Terrier (adopted Jul 2011)
Peewee - Jan 2006 - 8 lb Chihuahua (adopted May 2009)
Myka - Nov 1998 to Jan 2010 - 85 lb American Pit Bull Terrier cross
Lacy - Sept 1992 to July 2003 - 18 lb Reg Shetland Sheepdog