Scheme of the estrus synchronization protocols in experiment 1. Cows in resynch group were synchronized by CIDR-EB (CIDR on day-10, PG on day-6, Estradiol Benzoate (EB) on day-2. CIDR withdrawal on day-7, TAI 48 h later was marked on day-0). On day 14 post TAI previously used autoclaved CIDR was inserted for 7 days. On 23rd day post TAI GnRH was injected intramuscularly. Pregnancy diagnosis was done on day-30. In non-pregnant PG (Dalmazin, d-cloprostenol 0.150 mg; Fatro, Italy) was injected. GnRH (Dalmareline, lecirelin, Fatro Italy) after 48 h and TAI 16-20 h post GnRH. BS=blood sampling on day 14, 16 and 30 post TAI. CL area on day 30 post TAI. In control group (CIDR-EB) lactating dairy cows (n = 70) were enrolled without further treatment except AIDE (artificial insemination at detected estrus) between 18 to 30 days post TAI and PD was performed 30 days after AI, respectively.