Schematic representation of the 2 synchronization protocols. Cows in the CIDR-Select Synch group received a CIDR insert (CIDR; Eazi-Breed CIDR® cattle insert, Pfizer Animal Health, Zurich, Switzerland) and 10 μg of buserelin i.m. (GnRH; Receptal®, Veterinaria AG, Zurich, Switzerland) on Day 0. On Day 7, the CIDR insert was removed and 25 mg of dinoprost i.m. (PGF2α; Dinolytic®; Pfizer Animal Health, Zurich, Switzerland) was administered. The cows were inseminated at observed estrus according to AM-PM rule up to 120 h from CIDR removal (a). Cows in the 12-d CIDR group received a Controlled Internal Drug Release insert (on Day 0) and it was removed on Day 12. The cows were inseminated at observed estrus using AM-PM rule up to 6 d from CIDR removal (b).