There are all sorts of possible causes. Do you have rooks or jackdaws sitting on his back and pulling the hair out?, Is he itchy for some reason causing him to rub or pull it out himself. Have you checked for lice? I had an elderly mare who was very prone to lice, and she used to lose her coat in the way you have described. I also had another one whose hair used to come out in patches as she got older and I never did find out the cause!

It will grow back, but try to find out if something is causing it. 

Hello Jasper and welcome to the forum. 

Your old timer sounds like a typical donkey losing his winter coat.  I have 4 donkeys of varying ages and all, except one, look like old hearth rugs at the moment, not fit to be seen.

Mine never seem to lose their coats in the same way each year.  I think the weather has a lot to do with it and the type of winter they go through.  My old lady never gets her summer coat til the end of August, she looks stunning for about 3 weeks and then starts growing her winter coat again.

Creepy crawlies do not have to be in residence for donkeys to look like nothing on earth!

Hi all

Great news my old little man has a lovely new coat growing. All the bald patches are covered now and hopefuly he will have a new coat for winter time. Thanks for all your advise. I also got him a girlfriend a while ago, when he saw her his face, well it was like he had a great big smile on it, he was grinning from ear to ear. They are the best of friends now but it took a while.

Jasper