Reprod. Nutr. Dev.
Volume 46, Number 4, July-August 2006Symposium: Influence of nutrition and socio-sexual context on reproduction and survival of the young in goats and sheep
|Page(s)||417 - 429|
|Published online||07 July 2006|
Male-induced short oestrous and ovarian cycles in sheep and goats: a working hypothesisPhilippe Chemineaua, Maria-Theresa Pellicer-Rubiob, Narjess Lassouedc, Gley Khaldid and Danielle Monniauxb
a INRA, Département "Physiologie Animale et Systèmes d'Élevage" 37380 Nouzilly, France
b INRA, CNRS, Haras Nationaux, Univ. F. Rabelais, UMR Physiologie de la Reproduction et des Comportements, 37380 Nouzilly, France
c INRAT Laboratoire de Productions Animale et Fourragère, Ariana, Tunisie
d INAT, Chaire de Productions Animales, Tunis, Tunisie
(Published online 7 July 2006)
Abstract - The existence of short ovulatory cycles (5-day duration) after the first male-induced ovulations in anovulatory ewes and goats, associated or not with the appearance of oestrous behaviour, is the origin of the two-peak abnormal distribution of parturitions after the "male effect". We propose here a working hypothesis to explain the presence of these short cycles. The male-effect is efficient during anoestrus, when follicles contain granulosa cells of lower quality than during the breeding season. They generate corpora lutea (CL) with a lower proportion of large luteal cells compared to small cells, which secrete less progesterone, compared to what is observed in the breeding season cycle. This is probably not sufficient to block prostaglandin synthesis in the endometrial cells of the uterus at the time when the responsiveness to prostaglandins of the new-formed CL is initiated and, in parallel, to centrally reduce LH pulsatility. This LH pulsatility stimulates a new wave of follicles secreting oestradiol which, in turn, stimulates prostaglandin synthesis and provokes luteolysis and new ovulation(s). The occurrence of a new follicular wave on days 3-4 of the first male-induced cycle and the initiation of the responsiveness to prostaglandins of the CL from day 3 of the oestrous cycle are probably the key elements which ensure such regularity in the duration of the short cycles. Exogenous progesterone injection suppresses short cycles, probably not by delaying ovulation time, but rather by blocking prostaglandin synthesis, thus impairing luteolysis. The existence, or not, of oestrous behaviour associated to these ovulatory events mainly varies with species: ewes, compared to does, require a more intense endogenous progesterone priming; only ovulations preceded by normal cycles are associated with oestrous behaviour. Thus, the precise and delicate mechanism underlying the existence of short ovulatory and oestrous cycles induced by the male effect appears to be dependent on the various levels of the hypothalamo-pituitary-ovario-uterine axis.
Key words: male-effect / ovulation / corpus luteum / cycle / oestrus / uterus
Corresponding author: Philippe.Chemineau@tours.inra.fr
© INRA, EDP Sciences 2006