[elissama101]

Usually the best thing to do with any abcess caused by bacterial infection in a horse is to let the abcess(es) rupture then start a course of antibiotics. Keep the animal on stall rest with monitored exercise (don't want to contaminate paddocks / other horse areas with bacteria.

Adding electrolytes to the feed or water can also be helpful to increase the animals water consumption. Just like people they say when sick to increase fluids - helps get things moving.

You probably want to start with a course of IM (intramuscular) antibiotics then switch to orally dosing after 10-14 days. (your vet will make the correct calls here)

Unfortunately, if you have an internal rupture it will probably make more sense to euthanize that to operate - operations on horses are very expensive and frequently the horse doesn't come out the same way it went into it. (Problem with such a large animal)

Good luck!

EDIT: if you do end up on antibiotics moniter the pony very carefully. They can become easily 'backed up' from the drugs and this can lead to lack of drinking, colic, death. It is a good idea to put horses on antibiotics on a hot mash (with mineral oil) at least every other day.