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.

[Click here to read more about kick injuries to herdmates.]

Fortunately, a horse’s body is pretty good at resorbing blood over time. With no intervention, the hematoma will gradually get firmer and smaller, until it disappears.

However, complications can develop. If the causal trauma broke the skin, even with a tiny puncture you cannot see, there’s a chance that bacteria entered the hematoma space and an infection could take hold. In these cases, the lump is likely to be warm and painful and the horse may run a fever. Call your veterinarian if you suspect your horse has an infection.

You’ll also need your veterinarian if your horse becomes lame or the hematoma itself seems sore. Some can be drained to relieve pressure and make the horse more comfortable.

This article first appeared in EQUUS issue #465, 

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