try a food for at least 6 weeks -unless the dog is throwing it up or a obvious thing as the stains form the eyes. I would guess , fish might be a culprit for that dog. or if the dog has a white face . lots of problems there. try hydrogen peroxide on a paper towel. (careful to not get any in the eye) it works quickly !
sadly 99 % of the food companies change the sources of the meats, and just because one dog hasn't had tear stains until now, means that there has been a change in the food, processing/sources ! large pet food companies that are to big will buy from what ever source they can for cheaper. all in due time. a smaller family owned company like FROMM will only buy from their reputable source. and they tell me that it is shipped in daily, and everything is inspected also daily. they only use vegetable and fruit sources for the vitamins in their food. they never use man made vitamins. the nutritionist is on hand for you to talk to any time that you call.and they have voluntarily signed up for the notify owners if any problems arise in or with any of their food! as has several others . the only other food that I would ever feed a Bulldog,---to guarantee that in 4 to 6 years they would/shouldn't have any internal organ failure!
other than Fromm, is great 4life- or natures variety. (and they are not up to par with the pre and pro bitotics like the other two foods, and are balking at doing so .) they feel they have been around long enough not to need to . -- wrong- if it is not in writing in the guarantee !!! it may as well not be printed.
because only a trace amount is likely in it . by law that's all that's necessary to list it.
please keep the protein down around 30 or less. or look for hot spots to pop up any time. and often the bad stools are form an unbalance in protein levels or an intolerance to a protein. merrick is a good food too. but also not up to letting us know what temp it is cooked at or for how long. fish also upsets many bullies tummies. although I have had great luck with salmon and my gang.