Our last "hold-out" mare, a mini, did that to us this year. It was a first for us too. She dripped sticky milk for almost a week!
Looking back, I wonder if she was holding onto that baby for just a little longer on purpose. (Not to scare you, just my observation.) The foal was tiny. He came out presented properly but with the placenta right behind him so I had to cut the cord. Also, he was down on his rear legs AND hyper extended on his front!
Because of the placenta situation, he was a little oxygen deprived, so was a sleeper foal and I had to milk mom and feed him for his first 12 hours until he seemed to "catch up" and found the faucets! Also, his legs started improving after his first 24 hours. He is now just over a week old and his legs are almost normal now.
Kay, I'm just theorizing that with our mare, maybe something told her to keep a hold of that baby to help it mature just a little bit more. I can't imagine what our colt would have been like if it had been just a week or two younger.
Fortunately, he is doing wonderfully now and romping and bucking and driving his mom crazy.
MA