Determination of ovulation time in bitches based on teasing, vaginal cytology, and ELISA for progesterone

The estrous cycle of 16 mature mongrel female dogs was monitored to evaluate the accuracy of teasing, vaginal cytology and quantitative ELISA progesterone assay to determine ovulation. The dogs were presented to male, and blood samples and vaginal swabs were taken daily during proestrus and estrus. Selected serum samples collected during estrus were assayed for endogenous LH by radioimmunoassay (RIA). Plasma samples collected during proestrus and estrus were assayed for progesterone with a commercially available ELISA kit. Ovulation was considered to take place 48 h after the preovulatory LH peak. Vaginal cytology smears were stained with Wright's stain and evaluated for the percentage of superficial squamous cells. Day 1 of diestrus (Day 1) was defined as a drop of 20% or more in the total number of superficial cells. Two standard curves (linear and best fitted curves) commonly used with ELISA were compared together and with the RIA progesterone assay. Ovulation was estimated to occur when progesterone concentration was 4.9 +/- 1.0 ng/ml (mean +/- SD, n = 15), with a range of 3.4 to 6.6 ng/ml. Based on vaginal cytology, ovulation took place 6.9 +/- 1.6 d (n = 15) after 80% of the squamous cells were superficial and 6.8 +/- 1.4 d (n = 16) before Day 1. Ovulation took place 2.1 +/- 3.9d (n = 11) after the first day of standing estrus and 8.8 +/- 1.5 d (n = 10) before the last day of receptivity. The two standard curves were found parallel to each other and to the RIA progesterone assay. Based on the results of the present study, ELISA progesterone assay and determination of the first day of estrus by vaginal cytology are reliable methods for predicting ovulation, whereas the last day of receptivity as determined by teasing and Day 1 as determined by vaginal cytology are reliable methods to retrospectively estimate ovulation time.