Reprod. Nutr. Dev. 43 (2003) 167-177
DOI: 10.1051/rnd:2003015

Amplitude of the plasma melatonin nycthemeral rhythms is not associated with the dates of onset and offset of the seasonal ovulatory activity in the Ile-de-France ewe

Luis Ángel Zarazaga^{a, b}, Benoît Malpaux^a and Philippe Chemineau<sup>a

a</sup>  UMR INRA-CNRS-Université de Tours, Physiologie de la Reproduction et des Comportements, 37380 Nouzilly, France
^b  Present address: Universidad de Huelva, E.P.S., La Rábida, 21819 Huelva, Spain

(Received 23 October 2002; accepted 19 February 2003)

Abstract
We investigated if absolute (nocturnal) or relative (nocturnal/diurnal ratio) plasma melatonin concentrations were associated with the seasonal ovulatory activity in Ile-de-France ewes. Ninety-six and 121 ewes in two different groups of the same flock were used to determine the potential existence of a relationship between melatonin concentrations at the summer and winter solstices, and the dates of onset and offset of the ovulatory activity, respectively. The dates of the first and last ovulations were estimated by assaying progesterone in plasma samples taken once weekly. Mean SEM (1) plasma melatonin concentrations at the summer solstice and at the winter solstice were 302.4 19.4 and 412.0 18.7 pg mL ^-1, respectively, (2) date of onset of the breeding season 29 Jul. 1.6 days, (3) date of offset of the breeding season 24 Jan. 2.2 days. In spite of a large variability in the different traits studied here, the analyses of correlation and regression indicated that neither the absolute nor relative melatonin concentrations were significantly related with the dates of onset or offset of ovulatory activity. Therefore, we concluded that absolute or relative plasma melatonin concentrations are not linked to the seasonal breeding activity, in Ile-de-France ewes.

Key words: sheep / melatonin / reproduction / seasonality / genetics

Correspondence and reprints: Philippe Chemineau email: Philippe.Chemineau@tours.inra.fr

© INRA, EDP Sciences 2003