Accuracy of canine parturition date prediction from the initial rise in preovulatory progesterone concentration

Accurate prediction of parturition date is useful for clinical management of canine parturition. For nearly all normal canine pregnancies, parturition occurs 64-66 days from the LH peak, the timing of which cannot be differentiated from the initial sharp rise in serum progesterone (P4) concentrations. We sought to determine by retrospective analysis if prebreeding serum progesterone concentrations could accurately predict parturition date. Serum progesterone concentrations recorded as serial samples from 63 bitches (19 breeds) were analyzed. Progesterone concentrations were measured by radioimmunoassay (RIA) or chemiluminescent immunoassay (CLIA). The CLIA method was validated for use in determining P4 concentrations in canine serum and results were comparable to those obtained with RIA. Bitches were grouped by nonpregnant body weight (BW) and litter size (LS). Day 0 (D0), the day of preovulatory rise in serum P4, was defined as the day that P4 concentration rose to > or =l.5 ng/ml and was at least twice the baseline concentration. The predicted parturition date, 65 days following the day of preovulatory rise in serum P4 (D65), was compared to actual parturition date, the day the first pup was delivered. We determined that mean P4 concentration at D0 for all BW groups was 2.02+/-0.18 ng/ml and there was significant variation in P4 concentrations between BW groups after D1. In addition, we determined that the accuracy of parturition date prediction within a +/-1, +/-2, and +/-3 day interval using prebreeding serum progesterone concentrations was 67, 90, and 100%, respectively, and that the accuracy was not affected by body weight or litter size.