I have a 3 year old male New Foundland that is losing his hair. It came on suddenly. He now has large bald spots on his back/shoulders and on his rump. Yesterday I could not see "sores" on his skin but today there is a few. He is housed with 3 female Newfies, two of which just went out of heat. I don't know if that could have anything to do with it. Could someone please help me?
Hair loss can be a sign of many problems, I think a trip to the vet is probably in order. Hypothyroidism is one thing that can cause hair loss, and that can be a genetic problem, so if your breeding him, you'll probably want to rule that out. Any trouble maintaining his weight?
I agree with the others. A trip to the vet and some blood work done is a must. Stress could be a possibility, but usually doesn't leave one bald spot, unless he his pulling his hair out. It usually is all over balding. Good luck
Another possibility is hot spots, especially since you mention you see some small sores now. They can come on very suddenly and any dog (or cat) can get them, but they seem to be more prevalent in long haired breeds. I have never had a problem with any of my dogs although two of my cats got them (once each). They can be caused by a number of things, including stress, which I agree could have been caused by him being in close contact with two females in heat. If it were me I would take him to the vet to be checked since there are so many different things it could be.