Swelling on both hocks

[DSCC]

My mare has soft, fluidy type swelling on the outside of both hocks. She is not lame and not bothered when I press them. I think it thoroughpin but may be too low for that as in a pretty straight line between the point of hock and front of hock where it bends. Does anyone have any ideas?

 

[Red-1]

Mine is more squishy there in hot weather. Once the winter comes it all seems to tighten up. Every year I think it is going to develop into something, but he has never been lame on it, and every year it goes away again when it is colder.

 

[Ditchjumper2]

Bog spavin ?