The precision of peri-oestrous predictors of the date of onset of parturition in the bitch

•The precision with which predictors predicted the onset of parturition was compared.•The predictors were LH, progesterone 6 or 16 nmol/L and cytological diestrus (D0).•D0 was the most precise predictor of parturition.•The precision was ±1 d, ± 2 d and ±3 d in 88%, 99% and 100% of 242 pregnancies.

Precise prediction of the date of onset of parturition in the bitch is clinically important. The study compared the precision with which four peri-oestrous predictors predict the date of onset of parturition. The predictors evaluated in 24 bitches were: the date of the first or only day of the LH surge, the date on which the concentration of progesterone in the blood plasma first exceeded 6 nmol/L, the date on which the concentration of progesterone in the blood plasma first exceeded 16 nmol/L and the date of onset of cytological dioestrus. Among the 24 bitches, the date of onset of cytological dioestrus predicted the date of onset of parturition with greater precision than the other three predictors. Following the evaluation of another 218 intervals between the onset of cytological dioestrus and the date of onset of parturition, it was shown that the onset of cytological dioestrus predicted the date of onset parturition with a precision of ±1 d, ± 2 d and ±3 d in 88%, 99% and 100% of the 242 pregnancies. This study concludes that the first day of cytological dioestrus is a useful predictor of the date of onset of parturition.