“…Therefore, work into estrus synchronization of heifers remained concentrated on modifications of the MGA protocol. Initial work by Kesler et al (1996) attempted to decrease the length of time from removal of MGA to PGF2α injection. However, it was soon discovered that the optimal time for PGF2α injection would be 19 d following MGA removal (Lamb et al, 2000) due to the formation of overly mature, persistent follicles that would lead to decreased pregnancy rates.…”