Fig. 1

Diagram of the experimental design. Estrous cycle of non-suckled, multiparous Nelore cows was synchronized and estrus was detected (D0; n = 104). Animals were assigned randomly to one of the four treatment combinations on a two by two factorial arrangement of the following treatments: vehicle (Non-iP4) or supplementation with 150 mg of injectable long-acting P4 (iP4) on D4 and transfer of none (0-ET) or 5 in vitro-produced blastocysts on D7 (5-ET). Blood samples (BS) were collected on D4, D5, D7 and daily from D14 to D20 to determine circulating P4 concentrations. BS are also collected every 48 h between D14 and D20 for analysis of ISG15 relative abundance. From D4 to D20, ultrasound (US) scanning was conducted to record total CL area and CL area containing color signals of luteal blood flow for evaluation of CL growth and regression. On D30, pregnancy diagnosis (PD) was based on detection of an embryo with heartbeat at US. Those cows from 5-ET groups were classified retrospectively as experiencing early embryonic mortality (EEM), late embryonic mortality (LEM) or diagnosed as pregnant on D30. Those cows from 0-ET groups were classified as cyclic