Electromyographic properties of the myometrium of the pony mare during pregnancy.

Recordings of uterine electrical activity were made from 5 pregnant pony mares from Day 141 to 320 of pregnancy. Three types of activity were identified. Short, medium and long bursts were quantified as the percentage of time each occurred during the hour analysed and further categorized according to frequency, amplitude and duration. The uterus was most active during the early stages recorded and became increasingly quiescent after Day 240. Short-burst activity was greatest when the uterus was most quiescent. Long bursts showed the greatest percentage of activity until Day 220 and then decreased. Medium-burst activity was present throughout the period studied and high amplitude synchronous medium bursts peaked at Day 221-240.