BTW - 19 - 21 days was the cycle found by researchers in WA back in the 40s. That is an average, and unless you know when a doe last went into heat, the number is less meaningful. The average BT doe peak estrus (on the bell curve - as Bone pointed out) is somewhere around 7 - 10 Nov. The next, possibly third cycle kicked in a a few days ago and is somewhere near peak (for un-bred does) right now. 28 day cycle is quoted by a lot of writers, but there are no statistics to support those numbers.