Mating in the rhesus monkey (Macaca mulatta) after conception and its relationship to oestradiol and progesterone levels throughout pregnancy

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Abstract
Behavioral and hormonal data were collected throughout pregnancy in captive rhesus monkeys. Heterosexual pairs observed in daily time-limited mating tests showed 2 distinct periods of increased sexual interaction, as measured by the incidence of ejaculation. One period was coincident with the preovulatory estradiol peak, while the other occurred between the 6-10th wk of pregnancy. The positive relationship found during the menstrual cycle between the ratio of circulating estradiol:progesterone and degree of sexual activity continued for the first 8 wk of pregnancy. Sexual activity ceased in the 2nd half of pregnancy despite a continued high estradiol:progesterone ratio.