The Crestar ear implant releases synthetic progesterone (acting as an artificial corpus luteum). Progesterone stops production of hormones which would trigger heat.
An oestrogen intra-muscular injection at the same time as the implant will knock out the cows natural corpus luteum. The result is a precisely timed heat (95% of animals) once the implant is removed after 9-10 days.
Only one fixed time insemination is needed – 48 hours after implant removal for heifers, 56 hours later for cows.
An injection of PMSG hormone on implant removal for beef animals will help initiate a fertile heat. It starts cows cycling and once induced to cycle they will continue to do so with each heat becoming more fertile.
All cows should have calved at least 45 days before Crestar implantation.