sorry but that IS a fistula
and open hole like that is called a fistula..
Did the vet give you any antibiotics? Say 'why' he has an enflamed butt area?
I can say what the red 'thing' is right by his anus, but those holes are fistula's.
Fistula's can develop for a variety of reasons, infected anal glands, the gland 'stuff' backs up, has no where to go, so tracks begin/expand and push the fluid out. Blown anal glands will also produce fistulas.
Alot of PF dogs have other issues, allergies/ibd / sibo.
I see your in MA, are you near Angell Memorial?
If my dog, this is what I would do,,shave up the area, take him to someone who is 'savvy' in fistula's. Keep the area clean, pack some Desitin into those fistula's.
He DOES need to see a vet tho, they should have him on an antibiotic, they should shave up the area, go from there..
I'd take him to Angell to..
You can also look here
There should be a section with vet's names in your area that deal with fistula's.
Been there done that with TWO dogs..My vet who's become fistula savvy from my own dogs is Chris Ficke at Chester Vet/ Chester CT..
Definitely back to the vet