Lump on horses hindquarter

[Ndistler]

I have this mare that has a lump on her right rear hindquarter. I just happened to notice this last week, but thought that it may have been a reaction from when the vet gave her multiple shots a couple weeks ago, because my other mare has that but i noticed this one was bigger today than it has been. What could it be and do I need to have a vet come out to take a look or is it something I can treat myself?

 

[a kind of magic]

Have you a picture?

 

[putasocinit]

Either way I would ice pack it, if it is an abscess it will come to a head and if it is swelling it will go down, give it a week with ice packing