Is it ok to feed MSM to lactating mares?

We have a Mare who has a ligament injury to her Hock, she has been x-rayed and all clear on that front, Now its just a waiting game. The Hock is still very swollen and i know will be for some time, there is no rush to get her back to work as she has a foal at foot, I have used MSM with my other horse and had grate results, just wanted to know if it is safe to feed while she has a foal at foot?