Your horse has a large lump on his hindquarters, about the size of a softball, that wasn’t there yesterday. The lump is slightly squishy and the same temperature as the surrounding skin. He isn’t lame or in pain. What’s going on?
Chances are you’re dealing with a hematoma, an accumulation of blood in tissue spaces. Hematomas typically form after a trauma, such as a kick from a pasturemate. The force of the blow separates tissues, creating a space, and ruptures vessels that allow blood to spill into that space. The result is a large, firm lump that forms quickly---literally overnight in some cases.
Fortunately, a horse’s body is pretty good at resorbing blood over time. With no intervention, the hematoma will gradually get firmer