Hello,
Thank you for sending your question to Just Answer!
With the symptoms you are describing- a lump in your horse's neck and running a fever, it sounds like he has been bitten by something or kicked by another horse.
Both of which needs to be checked by your veterinarian, if the fever is high.
What is your horses temperature?
Where is the lump?
How big?
I will await your reply and give you furter information. Thank you, Tammy
