We recently rescued our dog (6-12 months old), who was very undernourished and slept quite often. As we've done with other pets, we attempted to crate train him. At first, it didn't appear that he had any issue with the crate and would not bark or show any signs of distress.
This changed once we took him to the vet for the first time. He received some pills and vaccinations to prepare him for the being around other dogs. That night, he began barking quite loudly in his crate for 10-15 minutes before giving up and going to sleep.
Is it possible that the vet gave him some type of medicine that could have caused this change in behavior? Or, is this behavior symptomatic of his health quality increasing, and with that, additional energy to express his distaste for being crated?
No matter what the reason, are there any suggestions for dealing with this behavior?