Suppressed copulatory behavior and ovarian function in lactating Japanese monkeys (Macaca fuscata fuscata) during the mating season |
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Authors: | Fusako Mitsunaga Masumi Nozaki Keiko Shimizu |
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Institution: | (1) Primate Research Institute, Kyoto University, Kanrin, 484 Inuyama, Aichi, Japan |
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Abstract: | The influence of lactation on copulatory behaviors and ovarian functions was studied in Japanese monkeys (Macaca fuscata fuscata) during the mating season. Three lactating females were housed in an outdoor group cage with their infants, and three nonlactating
females were housed in an adjacent outdoor cage. They were mated by introduction of one of four rotationally chosen males
into the females' cage, for two hours three times a week; the occurrence of ejaculatory copulations was recorded. Blood samples
were collected on each observation day, and plasma levels of estradiol, progesterone, and luteinizing hormone (LH) were measured
by specific radioimmunoassays. In nonlactating females, plasma estradiol increased during the transition into the mating season,
and rose to levels over 90 pg/ml for the first time on about 50 days before the first ovulation. Shortly after plasma estradiol
exceeded 90 pg/ml in the nonlactating females, the onset of ejaculatory copulations occurred. They received ejaculations continuously
up to the early ovarian luteal phase. On the other hand, in lactating females, there were lower levels of plasma estradiol
(below 90 pg/ml) during the transition into the mating season, and they received no ejaculation during that period. Two of
the three lactating females ovulated only once, and they received ejaculations only during the periovulatory period, coinciding
with the rise of their plasma estradiol levels over 90 pg/ml. The remaining lactating female remained anovulatory and received
no ejaculation throughout the entire mating season. These results have demonstrated that the low sexual activity of lactating
females is clearly correlated with low levels of plasma estradiol due to suppressed ovarian function. |
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Keywords: | Lactation Copulation Estradiol Progesterone Macaca fuscata fuscata |
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