Any advice? I have a 4 yr old elkie who has suffered from the odd small cyst.They have usually bust and then I have expressed and cleaned them and they have gone. However he had one a few weeks back which has developed into a large lump.1 is now about 2inches across and seems to be slightly painful when pushed.
Archer

That sounds to me as if this is a cyst that has got infected and is turning into an abscess Archer.

Think a trip to the vet is called for.

My old boy has a wart on the side of his leg, which causes him no trouble at all, but very occasionally it gets infected and discharges pus.  I think it is probably because it is on his elbow and gets rubbed every now and again.