Urinary LH, plasma LH and progesterone and their clinical correlates in the periovulatory period of domestic bitches.

Ten bitches were examined daily from pro-oestrus until metoestrus to correlate endocrine, vaginoscopic and cytological assessments of stage of the oestrous cycle. It was considered that oocytes were fertile by 4 days after the LH peak assuming a 2 day lag before ovulation and a further 2 days for oocyte maturation. Eight bitches showed a plasma LH peak and five bitches showed a peak in urinary LH, which corresponded to the plasma LH peak. Plasma concentration of progesterone increased in all bitches. Initially, this coincided with the preovulatory LH peak and reached values of 7.7 +/- 0.6 ng ml-1 4 days later. The peak in number of a nuclear vaginal epithelial cells and the onset and peak of vaginal mucosal shrinkage with angulation occurred on average 2.4 +/- 1.5, 2.1 +/- 2.4, and 6.1 +/- 1.1 days after the plasma LH peak, respectively, giving sufficient precision to be of practical value in estimating the fertile period. However, the onset of vulval softening, changes in rectal temperature and colour of the vulval discharge varied considerably. Nine of the bitches were mated at the time of highest percentage of a nuclear cells, coinciding with the onset of the period of vaginal mucosal shrinkage with angulation. Eight became pregnant. Selected clinical parameters are therefore useful in predicting the optimal mating time of bitches, as is detection of plasma progesterone concentration higher than about 8 ng ml-1, but the latter appears to be the most reliable method. Detection of the urinary LH peak was more difficult and as yet offers no practical advantages except from the point of view of easy sample collection.