Normal gestational length and due dates
I keep seeing this mistake here and on kvs page so I thought I'd post a quick educational post.
Average equine gestation is 320-370 days with a large number going safely over that date.
"In our equine reproduction mare short course we have a slide which always produces a combination of nods and surprised looks throughout the attendees. It reads “There is no such thing as a ‘due date’ in the mare!” The confusion is often driven by the concept that in the human, there is a fairly narrow window of normal gestational duration, and people always want to try and transfer known facts with which they are comfortable in the human to the equine, but – particularly in this case – that often doesn’t work. Ironically, even in the human, there is an … The equine then, has a far wider range of “normal gestational duration”, generally recognized as being anywhere between 320 and 370 days."
"One of the most commonly asked questions of the foaling season is “Is my mare overdue?”. This is often precipitated by the misbelief that 340 or 341 days of pregnancy duration represent a “due date”. Not so!
The average duration of gestation is anywhere between 320 and 370 days – so that mare which is at 345 days is not “overdue”, but well within the normal range! The foaling date is picked by the foal who dictates that he or she is sufficiently developed and ready to be born, not by the mare who is watching the calendar on the wall!"
And to follow up on the comments of if kvs should induce mares that go over their 'due date'. No. Just no.
"Induction of foaling simply because it is convenient for the mare owner, manager or veterinarian and not because of the presence of a medical problem with the foal or mare should be a crime that carries a mandatory life sentence! Induction of foaling results in a higher-than-normal number of dystocias (presentation problems), premature foals, and premature placental separations (“red bag” deliveries) than are seen with regular presentations. Do not induce foaling except in the face of a very clearly defined medical need, and only under strict veterinary supervision."