Could this be a snake-bite?

Ww live in drought-ridden central Tx  and that is causing snakes to be more active.  We think our donkey has possibly been bitten by one.  The ridge that runs under his mane is swollen, especially on the left side.  It feels like it is fluid-filled. He was missing for a day, then yesterday he showed back up in the pasture and walked to the fence, taking short, slower steps.  I don't think he was feeling well but no fever. We didn't see any fang marks anywhere.  Does this sound like a snake-bite?  Copperheads, Rattlesnakes and Water Moccasins are indigenous to our area.

[lindasp62]

It is difficult to say from here, especially as you say you cannot identify any markings.  The best thing would be to contact your veterinarian as soon as possible to determine the cause of his swelling and malaise.