Will Falconer, DVM Moderator
Sandra, this may forever be a mystery! I thought I'd learned it when someone reported a correlation with grain in or out of the diet. She'd seen it come and go with grain, so it seemed pretty clear. I think the clearest thing is, tearing is a discharge. Discharges appear when the body is working against something, trying to get well. Your homemade food is pure enough that your dogs find no need to discharge, and when they eat prepared food, they are less well, for what ever reason, and start up discharging.
Best I can surmise from your experience. Are the two related?