Recently, a small series of screening experiments have been conducted with a view to identifying synthetic steroids of high activity for control of the oestrous cycle in mature Friesian heifers. Five synthetic steroids and progesterone were tested in cyclical animals. The activity of the steroids was assessed by their ability to suppress both oestrus and ovulation following a series of daily injections. The steroids were all chosen on the basis of their biological activity profiles in conventional laboratory animal bioassays.
The synthetic steroids were: