quote MCS Miniatures " I read they will usually foal 2-4 weeks after you're first able to express fluid, would you agree with that? "
Not set is stone but yes mares will present that way. Of course then the same mare who was text book for years will drop a foal without even having a bag the day before.
You can't depend on one sign.
You are doing good so don't get too nervous! Since you've observed her closely these last weeks you'll spot the differences in her regular behavior that will alert you to imminant foaling signs.
Something to watch for other than colostrum, loosening of the tail head and swelling and elongating of the vulva -- you may notice her being restless, looking at her sides, getting up and down. She'll be rolling to position the foal. The foal will need to shift from it's position on its back
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and rotate (as shown above) until its head and forelimbs are extended in the birth canal like this:
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Some other signs you may see are: pawing, doing a lot of yawning, pushing her butt against the wall. When its almost time you'll probably notice more manure than usual, she'll poop... a LOT and in my experience it will get loose like cow patties, and as contractions progress, she'll be sweating.
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Normal birthing presentation:
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Do you have a foaling alarm on her? I'm sorry if you already said and I missed it.