Plasma progesterone profiles in Beagle bitches with and without the whelping experience.

The aim of this study was to investigate differences between the progesterone profiles of Beagle bitches with (multiparous) and without (nulliparous) the whelping experience and to examine whether the selection of bitches by progesterone analyses before the programmed mating improved the whelping rates. In the first experiment, the progesterone profiles of nulliparous and multiparous bitches were evaluated from Days 1 to 13 (onset of prooestrus = Day 0). The mean duration of the elevation in progesterone levels (> 2 ng/mL) after the onset of prooestrus tended to be approximately 1 day shorter in nulliparous bitches (7.7 days) than in multiparous bitches (8.5 days). In the second experiment, progesterone analyses in the bitches were carried out once on Days 4, 5 or 6. Bitches with progesterone levels of > 10 ng/mL were excluded from mating because it was unclear when the progesterone levels reached > 10 ng/mL considering the optimal date for mating. No significant differences were observed in the percentages of bitches excluded from mating and in the whelping rates of the mated bitches between the groups, irrespective of the day of progesterone analysis and the type of bitch. In conclusion, the initial elevation of progesterone levels was of shorter duration in nulliparous bitches. The selection of bitches by the measurement of progesterone levels once before mating was not effective for the programmed mating.