what is lump on shoulder ?

[mlb15]

Just looking for advice.My 3 year old cob came in with a tiny cut about 3 weeks ago (wasn't deep at all) there was slight lump,a week later a big lump appeared a few inches above where the cut had been,it is firm and slight heat to it so got the vet out.She said it probably an abscess but too hard of an area to feel all around it so gave him enough bute for a week and said she would like to scan to see if it is a chipped bone if the bute didnt help.It is still there,id say it has slightly went down and has changed shape.Anyone know what it could be and what would be the best thing to do next? Would cold hosing help or applying something to it?

what it looked like to begin with (with the cut)
http://s284.photobucket.com/user/ph...55_8907826081941027946_n_zpsvvwfly74.jpg.html
http://s284.photobucket.com/user/ph...88_4501938476778083799_n_zpsjwokqiq5.jpg.html

Turned into this
http://s284.photobucket.com/user/phoenixpics2015/media/Snapshot_703_zpsxghah2ep.png.html
http://s284.photobucket.com/user/phoenixpics2015/media/Snapshot_702_zpssuszea1z.png.html
http://s284.photobucket.com/user/phoenixpics2015/media/Snapshot_671_zps2i3w1uou.png.html

What it looks like now.I have circled it with white so you can see how it has changed shape.
http://s284.photobucket.com/user/phoenixpics2015/media/Untitled_zps7bgcgcek.png.html
http://s284.photobucket.com/user/phoenixpics2015/media/Snapshot_1092_zpsphzllnw9.png.html