assaysJugular blood samples were collected in 10 mL EDTA-treated tubes (Vacutainer, Becton Dickinson and Company,USA) on the day of the second PGF2dose, on the day ofthe onset of synchronized estrous (D0) and on day 5 afterestrus. The blood samples were promptly centrifuged at1500 × g and the plasma was stored at −20◦C. The lutealactivity was determined by assessing the concentrations ofplasma progesterone using a solid-phase radioimmunoas-say (Coat-a-Count®, Diagnostic Products Corporation, LosAngeles, CA, USA).