I was hoping to get a response back to my request for more information, but I don’t want you to go without an answer either.
It is likely a dominance issue between the two dogs. Dogs are pack animals and they use growls and nips to reprimand unacceptable behavior from a lower ranking dog. Alphas are supposed to get to eat first, own everything and just allow other dogs to have things and they by right should get treats and affection first as well. So if a lower ranking dog takes something that the alpha thinks is theirs then they will reprimand them with a growl or nip.
Sometimes owners contribute the tension. An owner might show affection for a lower ranking dog before the alpha. The alpha can not reprimand you (usually) and thus will take it out on the dog since they should have known not to go to you until the alpha had all the attention they wanted. Often an owner will feed or give treats to a lower ranking dog leading to a reprimand.
You can help the situation by recognizing the alpha dog and always feeding that dog first or show that dog attention first. This will help prevent situations where they might clash. Obedience training will help as well The following site is helpful in helping owners train their dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
Obedience training helps you control your dogs and as you gain control of them, they see you as the boss and as boss you decide who you want to show attention to and who gets reprimanded. That usually help with attacks that happen only when the owner is around.
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Since there have been recalls on certain foods, please check the following site to be sure the food your animals eat is not affected. If it is affected, contact your vet as soon as possible. Have your dog seen if they have any symptoms.