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The serum melatonin concentration during gestation is a little studied area among livestock.

The aim of this study was to focus on nocturnal serum melatonin concentration in connection to the reproductive cycle and gestation. The authors measured the blood serum melatonin concentration at different stages of gestation of nine pregnant Hungarian fallow donkey mares and nine non-pregnant controls at a nucleus farm located in Böszénfa. Blood sample were taken from the jugular vein into blood tubes containing EDTA during nights. Animals were kept in closed dark stable and samplings were done with use of red light at <1 lux.

ELISA Kit was used to quantify serum melatonin concentration. The obtained melatonin values were corrected according to the time to the winter solstice, the time to midnight, and the gestational age. Second degree and lowess curve fittings were applied to demonstrate the tendencies of melatonin concentration by time.

The highest melatonin concentration was found in both pregnant and non-pregnant groups of mares to be in the second hour following midnight. There was a clear tendency of the melatonin concentration to increase gradually in the second half of the gestation with a peak before parturition and a significant decrease occurring after parturition.

Pregnant mares appear to have higher melatonin concentrations than non-pregnant mares. Furthermore, it can be assumed that the melatonin concentration reaches its peak just before foaling, when the mare prepares for parturition, and at the same time gives her offspring a higher chance of survival with the higher melatonin supply.