My Australian Shepherd Is Aggressive Toward His Vet

My Australian Shepherd is 2 years old. I have had him since he was 8 weeks old. We live on an acreage and he doesn't have much interaction with humans or other dogs. He will bark at the occasional delivery guy and jump on him or nip at his heels.

I have taken him to several training sessions with other people and dogs. He also goes to doggy daycare 2 to 3 times a month. He has never been aggressive or vicious with people or dogs.

In the last 9 months he has started biting the Vet. My Aussie starts growling and then when the Vet tries to examine him my Aussie tries to bite him—not a nip, a bite.

I thought that my Aussie might be reacting to the mask that the Vet is now required to wear. ??? Would it be a bad thing to put a muzzle on my Aussie when we go to the Vet?

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