Hi HeatherMy mare Della had this. She started passing the purple goo (it was actually blood tinged mucous) at day 312. She passed it continually until she foaled at day 323. Della passed a ton - maybe a bucket a day.
If it is just a little bit it is probably just the mucous plug.
Della turned out to have several problems. She had a partially formed twin that was sloughing off. She ruptured a huge varicose vein. The blood was congealing in the vaginal vault, mixing with the mucous and being expelled.
We treated Della with Banamine, antibiotics. We did not do regumate because she was getting close to 320 and I did not want to trap the goo inside the uterus.
I would be happy to talk with the mare owner if you think she would like to.
Della had a huge filly who was very healthy with all things considered. Della had a few issues for 2 days post foaling but is doing so much better now.
Thanks
Genevieve