Like I posted previously, if the dog food you're feeding contains Red Dye 40, it is building up in their systems from day one, and the toxins are being passed on to your snakes.The fact remains my food choice takes a long time to negatively impact said rodents, and they will not live long enough to see the negative side effects.
Even though there aren't specific studies with that dye and pet snakes, there's been plenty of studies involving other toxins being ingested by prey and being found in and affecting the predator that eats them.
You're risking the health of your SNAKES by feeding dog food, not just the rodents.