??? fungal infection

Question
We have 2 Teddy guinea pigs, both male kept in an outdoor cage. they have hay for bedding in their sleeping area and wood shavings in their eating area. Tonight we were putting them back into their cage when I noticed a large area of hair missing on the lower back of one of them the hair comes out quite readily in clumps. The other one seems fine. Both of them are eating and drinking well. They have a diet of mixed veg, carrots,cucumber, peppers, celery, spinach and parsley.

Answer
I'm glad you included that they are Teddies, because Teddies seem to have an issue during summer months with "blowing their coats".  I raise Teddies and have had the same thing. If there are no scabs that you can see it's most likely not fungal. If there is no evidence of being bitten by his cage mate then he's going through this coat change.

Mine will get this terribly dry skin and their hair will begin coming out in clumps just as you describe. What I do for mine is a two fold treatment. First I do treat them for mites just in case. I treat all my herd regularly and still I occasionally have one or two with the telltale symptoms of mites. The 'V' shaped hair loss on the top of the back is a good indicator that there are mites.

The Teddies however seem to have their own little peculiarities, and summer coat blowing is one of them. After I've treated them with mites I get a comb with teeth small enough to get through the hair, but big enough that it doesn't pull too hard.

You'll find a great deal of loose hair, especially over the rump. When you run the comb through you'll find hair coming out in big chunks. They're not usually bald underneath these clumps and sometimes you can see small hairs where the coat is already replenishing itself.

I comb mine thoroughly and they almost look as though they've had a haircut. The first time I noticed this was with a sow that appeared to have hair over her rump that was much longer and standing up farther than the rest of her coat. That hair was all loose and combed out in clumps. After I combed her out the coat was even. It was just the loose hair that gave the illusion that she had a big dip in her back where the hair appeared to be shorter.

Now I watch for that kind of thing during the warmer months. My short haired pigs never do this, just the Teddies. Other breeders I know have the same problem. Once you've thoroughly combed him out give him a good bath.  The coat will grow back even and be beautiful again. And it doesn't take very long, less than a month.

I would bet that this is exactly what your boar is doing. It's just a kind of shedding that seems unique to Teddies. They are also more prone to dandruff than the other breeds. I have a friend in Australia who tells me he has the same issue with both his Teddies and Rex.  

Give this a try and please let me know how it turns out. I really don't think he's suffering from any kind of fungus, etc. He's just molting and shedding off the coat.