My horse developed sudden lameness in his right foreleg. He tries to avoid all weight bearing and is carrying the leg with it splayed out to the right. His hoof has been checked and it seems fine (he is barefoot and was trimmed about 10 days ago with no problem until yesterday). What sort of injury is this likely to be, and apart from rest (which is all he does), should he have any specific treatment? Thanks for any advice
Kim

Call the vet!! Any kind of lameness issue that can't be traced to a bruised frog or something simple can be VERY serious! How long has he been lame? Is he kept in the pasture?

A sudden lamness of the foot-fine yesterday, can't walk today- Is usually an abcess.
You must first rule out a trauma, look/feel for heat,swelling,cuts,lumps,scabs...From the shoulder all the way down to the ground.
Generally if it is an abcess you will feel heat in a generalized area of the hoof.
Best treatment-Soak the foot in VERY hot water and a half container of epsom salt mixture to hairline for 20 min. Dry with a towel, apply liberally to the bottom of the foot a mixture of epsom salt, icthammol ointment, [poultice -if wanted]. Place a piece of paper-feed bag paper works best- that is slightly bigger than foot size,bend edges up around outside edge of foot. To secure paper, wrap entire foot with vet wrap.
With luck, It will stay on for at least 8 hours. You should stall him to monitor his movement, but if you can't do that. Go over your wrap with duc tape, it will last a little longer.
If you are dealing with an abcess in no more than 3 days, your horse will be completely back to normal. Depending on the size and the location you may or may not see the hole where it came out.
If you can, it doesn't hurt to continue with the soaks and flush out with an antiseptic.
If you have gone more than a week, with no improvement or if it seems to get worse. Than you need to have a Vet diagnosis it for you.

Also do a google search on founder/laminitis. Those symptoms can be similar but need immediate veterinary help.

Sounds like an abcess! Get your farrier, or vet, out there to open it up and drain it. This will instantly provide relief for the horse. If left to itself it will more than likely come up through the laminae and out near the hairline. This can lead to more issues later as it will take some time to grow out.

Once drained treat as above.