Can mouth breathing be because of stress or pain?

I'm sure you're worried about your little duckling. It sounds like he is in very caring hands.

I'd say that gapeworm is unlikely.

I'd say that stress alone would not be the problem either. Heat is a possibility - how hot would you say that the temperature is where you keep your duckling? If it is comfortable for you then it should be ok for him.

I would be looking for some other kind of underlying issue though. When you look at his nostrils and eyes do they appear to be perfectly clear or is there any kind of discharge at all? Is the area around his eye swollen at all? These things would indicate a respiratory infection.

Another possibility is that his nostrils are blocked (e.g. with dried food). Do they seem clear to you? Can you see all the way through them and out the other side? How often does he have access to water deep enough to put his whole head into? When he gets this water does he put his head in and clear out his nostrils by blowing air through them? To encourage him to clean his nostrils out, you can put finely chopped greens in a bowl of water, or put them in a bath for him.

Has he had an access to long grass? See if you can open his bill and check for any obstruction, including under his tongue.

What kind of other problems has he had? Has he been to see a vet?

The poor little fella has had a battle, hasn't he.

I'd be tempted to keep giving him a bit of heat - maybe make it so it's about 75 - 80 degrees under the light? That shouldn't be too hot for him but it will give him some warmth if he needs it. At 3 weeks he shouldn't normally need heat but since he is not super strong I might give it anyway.

I think you are doing the right thing to continue with the vitamin supplement. It sure does sound like a vitamin deficiency but I wonder if there is also some kind of neurological problem as well that is contributing to the lack of co-ordination and muscle strength. He's obviously got a few developmental issues but you are doing the right things - vitamins, swim time for exercise... Also give him a bit of time out in the sun each day too, if you can, for vitamin D (keeping him safe from potential predators of course).

Apart from taking him to an avian vet for assessment I'd say to keep doing what you are doing. I'm sorry that that is not much help!

Sounds like it's plenty warm enough without the light then! I forget that it is still summer over your way :)

Yes, I have known it to take longer to correct a vitamin deficiency. As they grow, their need for vitamins continues to grow as well, and so sometimes you have to keep the vitamins up to keep pace with the growth rate. This is likely to be especially true of a large, fast growing breed like a Pekin. I had a friend with a Khaki Campbell female that kept on needing the vitamins till she was almost full grown (and she grew more slowly than normal too). She kept flipping on her back whenever she drunk water. But she ended up fine and normal sized.

So, don't give up hope just yet. Keep up the great work and wonderful care that you are giving him.

Yes, I can totally understand that!!! You must be exhausted...  Do you think he would be ok overnight without checking?

Maybe try giving him a nice big feed before bedtime and then just a small, shallow dish of water and propping him up beside it with a couple of wheat bags on either side of him or something supportive. Even a couple of soft toys. Maybe just try that for one night. He might be a tad messy in the morning, but then he can have a bath and he'll be good as new.