Strange lump on my horses neck?

I agree with the others that it may be a reaction to a bug or tick bite. Use your fingernail and scrape lightly back and forth across the entire bump, especially near the edges and watch to see if you can spot a tiny tick. If so, remove it and watch the horse for signs of Lyme's or erlychia. Call your vet during business hours to discuss it. It is not an emergency at this time. If it is not a tick bite, watch when you scratch it and see if the horse responds like it feels good or is itchy. Then it would be a bite reaction.

its more than likely a bug bite or a sting if its not oozing or giving your horse much pain, i would call your vet and notify them they may ask you to give your horse an antihistamine or put a topical cream on it to get down the swelling, keep a good eye on it if any thing changes or it gets bigger have the vet come out asap, look at the bump real well see if you can find a puncture wound, if it is a puncture wound it could have something stuck in the wound like a sliver or it could be infected good luck hope he heals up soon,

Well he could have a reaction to a bug bite. but i would say call your vet and just talk to him and ask him if he thinks he needs to come out or it will be fine.

i have had the same exact thing. it is a reaction from a shot/vaccine. even if he has not had a shot in a while, it is a reaction from an insect bite. so it's pretty much filled with pus and blood :( ew, but geta vet out there and have them inspect it and if it is what i think it is, then they will put a needle in it and suck all the crap out of it. yeah, so have fun with that and i hope he's ok :) gooooooooooooooood luck

or it could be strangles a virus that is the same as mumpes in children but the horse version. we had 2 horses last year get it very catchy. if that is what it is the vet will tell u to just let it run its course . it will pop like a vit smells like hell then a sore will form and will be gone in a few weeks. if you dont want any other horses your niehgtbers or whom ever you have to keep the horse from all other horses but like me I just let all my horses get it and i never have to worrie again.

Other than what everyone else has said, it could be an abcess. A splinter or something of that nature could have worked its way into his skin, leaving a cut. The swelling could be his body's response to a foreign object. If it does turn out to be an abcess, you may not even need to have it lanced and drained. Try shaving the area and applying poultice daily which could help draw out swelling and/or the foreign object,

I think you should scratch lightly where the lump is. My dog had it once had a lump. i scartched it and it got better. put water on it and wash your horse first