I am having the hardest time getting my pup to wear his collar. As soon as the collar goes on he lays in a corner and whines the entire time. Help!

Hello,

I need help with my 15 week old dachshund. I am having the hardest time getting him to wear his collar. I've had dogs my whole life and have never encountered this problem before. As soon as the collar goes on he transforms into a completely different dog. He lays in a corner and whines the entire time it is on him. He does not move! He won't eat, pee, or poop while it's on him. From previous experience, I decided to just leave it on him and he would eventually get used to it, but after 2 days he was the same. He didn't eat, pee, or poop. Just laid in the corner the whole time and cried. He didn't even go in his bed to sleep that night. After realizing that he could make himself sick, I decided to take it off. I praised and rewarded him for wearing it. As soon as it comes off, he's back to the same active, playful Doxie puppy. My vet advised that I try to put it on him for a few hours every day until he gets used to it, but that's been 4 weeks now, and now he runs and hides as soon as he sees the collar coming. He's still exactly the same when it's on him. Because of the collar issue I can't even put a leash on him. He acts like a pig about to be slaughtered when the leash is on him! It's horrible. He has got to get used to his collar, because it's slowing down the training time and I know that this is the crucial time to train him. I've tried different kinds of collars and even a harness, but it's still the same. Please offer me some advice if you can about my stubborn Doxie. I just don't know what else to try with him.

Thanks,
Casey