This study was conducted at the Sheep Farm pertaining to the Department of Animal Resources - College of Agriculture - University of Al-Anbar that located at Latitude 33° 20´ N during the period from 1/3/2013 till 22/12/2013. The objective of this study was to investigate the plasma melatonin levels of Iraqi Awassi ewes. Ten Awassi ewes of 2-4 years old and 41-54 kg live body weight were used in this study. Blood samples were collected from each ewe every 3h for 24h during spring equinox (21-22 March). Summer solstice (22-23 June). Autumn equinox (21-22 September) and Winter solstice (21-22 December).
The plasma melatonin levels were determined as well as light intensity. Temperature – humidity index (THI) and body temperature at the time of blood collected. The plasma melatonin levels showed a characteristic seasonal variation and the pattern of melatonin secretion of Iraqi Awassi ewes did not subjected to the normal rhythm of melatonin secretion (high at night and low or undetected at the day). The plasma melatonin levels seem to be highly variable among individuals. The absence of significant correlation was observed between light intensity and plasma melatonin levels. THI and plasma melatonin levels as well as between plasma melatonin levels and body temperature. It was concluded from this study that there was a significant difference in melatonin levels between different seasons.