(Pfizer Animal Health) Improves the timing and efficiency of cow and heifer breeding programs. Inserts are administered intravaginally, one per animal, releasing progesterone during the seven-day treatment period. For beef cattle an injection of Lutalyse must be given one day before insert removal. Removal of the insert on treatment day seven results in a drop in plasma progesterone, triggering estrus within three days. (Lutalyse is a prescription drug.) Applicator sold separately.