Influence of season of birth on onset of gonadotrophic and ovarian functions in young doe hares (Lepus europaeus).
The pituitary and ovarian responses to a monthly i.v. injection of 5 micrograms luteinizing-hormone-releasing hormone (LHRH) were studied in three groups of young doe hares, born in January-February (group I), in April (group II) or at the end of the breeding season (August-September, group III). The LHRH injection was always followed by a release of LH and progesterone, which did not differ among the three groups at 3 months of age. The pituitary and ovarian responses to LHRH increased gradually from the age of 3 months in groups I and III and from the age of 9 months in group II. One female of the ten born in January-February ovulated and reached puberty in June, at the age of 4 months, but with a weak pituitary response. The females born in April displayed a seasonally delayed puberty, at 9 months of age (two of five females ovulated in the next January). Four of the five females born at the end of the breeding season ovulated after LHRH when 5 months old (in February), with a full pituitary-ovarian response. The low pituitary response of group I in June-August, even if 10-20% of females ovulated after LHRH, suggests a need for a period of short days. Then, the most favourable conditions for the hare to reach puberty would be a period of short decreasing daylengths during the fall, followed by increasing daylengths after the winter solstice.
Caillol
M
M
Laboratoire de Physiologie Sensorielle, Institut National de la Recherche Agronomique, Jouy-en-Josas, France.
Mondain-Monval
M
M
Meunier
M
M
Rossano
B
B
D000367:Age Factors; D000704:Analysis of Variance; D000818:Animals; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology; D007793:Lagomorpha / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood; D010053:Ovary / Q000378:metabolism*; D010060:Ovulation / Q000502:physiology; D010507:Periodicity; D010902:Pituitary Gland / Q000378:metabolism*; D011374:Progesterone / Q000097:blood; D011555:Pseudopregnancy / Q000503:physiopathology / Q000662:veterinary; D012621:Seasons; D012741:Sexual Maturation / Q000502:physiology*; D013997:Time Factors
D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D007986:Luteinizing Hormone