Analysis of trough and peak of plasma melatonin circadian rhythm in ewes

This study evaluates the pattern of plasma melatonin during the trough and the peak of its daily rhythm. Blood samples from 8 ewes were collected every 3 h for a 48-h period. On the third day, blood samples were collected from 10:00 to 13:00 (trough) and from 20:00 to 23:00 (peak) every 20 min. Our results showed a robust daily rhythm of melatonin in both days of monitoring, with nocturnal acrophase. During the trough, a significant decrease was observed starting from the 10:40 with a progressive decrease about every 40 min. During the peak of the plasma melatonin daily rhythm, an increase was observed starting from the 20:40 with a progressive increase about every 40 min. These data could be taken in consideration to monitor the plasma melatonin variations during the 24 h, and for the administration of melatonin for breeding in ewes.