Oestrous behaviour and circulating progesterone and oestrogen levels during pseudopregnancy in the domestic rabbit

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Abstract
Using a range of positive and negative sexual behavior events, receptivity of 7 female rabbits was quantified from day 4 to 21 of pseudopregnancy and related to color of the vulva and patterns of circulating progesterone, estrone and estradiol. Females with a white vulva never accepted mating; the proportion of females with a red vulva submitting to mating varied from 13% on days 6-9 to 8-0% on days 14-21. In 3 females which were not receptive until day 18, estrogens were not detectable in peripheral serum; progesterone levels were maximal on days 10-13 and gradually fell to levels < 2 ng/ml on day 17. In 4 females which were sporadically receptive during pseudopregnancy, estrogen levels fluctuated between 15 and 140 pg/ml serum; the drop of progesterone began on day 13 and was more rapid.