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

Using a range of positive and negative sexual behaviour events, receptivity of 7 female rabbits was quantified from Day 4 to 21 of pseudopregnancy and related to colour of the vulva and patterns of circulating progesterone, oestrone and oestradiol. 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 80% on Days 14-21. In 3 females which were not receptive until Day 18, oestrogens were not detectable in peripheral serum; progesterone levels were maximal on Days 10-13 and gradually fell to levels less than 2 ng/ml on Day 17. In 4 females which were sporadically receptive during pseudopregnancy, oestrogen levels fluctuated between 15 and 140 pg/ml serum; the drop of progesterone began on Day 13 and was more rapid.