Predicting Ovulation is done by accurately detecting the initial rise in progesterone (from C1 to C2). Ovulation usually occurs 2 days after the initial rise in progesterone (from C2 to C3). The most fertile time to breed is 2 to 4 days after ovulation (C4).
To time C-section or whelping, test progesterone starting 58 – 60 days after first breeding (average gestation 63 days). A drop in progesterone to < 2 ng/mL (from C4 to dark C2 or C1) indicates whelping will occur within 24 – 36 hours.