APStracts 4:0273E, 1997.

The large variability in melatonin blood levels in ewes is under strong genetic influence. Zarazaga, Luis A., Benot Malpaux, Loys Bodin, Philippe Chemineau. Institut National de la Recherche Agronomique, Neuroendocrinologie Sexuelle, Physiologie de la Reproduction, 37380 Nouzilly, France, Institut National de la Recherche Agronomique, Station d'Am_lioration G_n_tique des Animaux, 31326 Castanet Tolosan, France

APStracts 4:0273E, 1997.

The present study was conducted to assess the degree of genetic determination of the variability in the mean nocturnal plasma concentration of melatonin in sheep. 312 ewes born from 18 males and with known genealogy were sampled at the summer and the winter solstices. The nocturnal plasma melatonin concentration was defined as the mean of 4 plasma samples taken at hourly intervals in the middle of the night (22:00-02:00). Identity of the father (P<0.001) and the solstice (P<0.05) were significant. Melatonin concentrations varied considerably among individuals (mean =338.4 pg/ml; SD 197.5 pg/ml; range 26.6-981.3 pg/ml) and between rams regarding the melatonin concentrations of their daughters (range from 202.9 pg/ml to 456.3 pg/ml). Inheritance was analyzed by a statistical model which allows discrimination of genetic effects from non-genetic effects and which estimates repeatability and heritabilty coefficients. Both the repeatability coefficient between solstices (0.60) and heritability coefficient (0.45 +/- 0.07; M+/-S.E.M.) were high. These results demonstrate that the variability in plasma melatonin concentration in ewes is under strong genetic control.

Received 18 August 1997; accepted in final form 4 December 1997.
APS Manuscript Number E385-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997