We bought an Angus cow and calf through a dispersal sale last year. When we went to pick her up she had a HUGE swelling on both the front left and right shoulders. We left it for about a month, one side went down the other did not. We took her to the vet and had it drained. I bet we got at least a gallon of white chunky puss out of it. Our vet told us it was from hitting the head catch too hard. It took several weeks to clear up, but she was fine. I would just watch it to see if it goes down, and if not you might have to drain it. Here is a pic of it.