blood red vulva on one side only

[indebtedfarms]

My mare has a thick line going down one side of her vulva. It is a deep blood red. She is at 312 days today and has several signs of labor. What do you think the blood red sign is? There isn't actually any blood it is just on the vulva. Thanks for the help

 

[Cathy_H]

Our mares do get darker inside as they get near to foaling. Rubbing can also cause it to get temporarily darker. I've been able to distinguish from a rub irritated red & the normal darkening. If there are any signs of tail rubbing then that may be why.