I have just noticed a bald patch on my lab's shoulder - he still has a little undercoat, but the coat is coming out in handfuls there.  It is about two inches across.  He has recently been castrated and a new pup has arrived this week.  Could this be stress or hormonal?  I will be taking him to the vet, but just wondered whether anyone else had experienced this?

I think it is important to get him checked out at the vets, but I've just been looking on this page and noticed a thread on Aloe Vera which some people seem to find helps with bald patches and hair loss.