Thyroid hormones are the key regulators of mammalian physiological functions. These hormones have been shown to be crucial for growth, development, energy metabolism and reproduction (Eiler, 2005). These hormones are known to be important modulators of developmental processes and general metabolism in mammals (Kaneko et al., 2008). They also play an important role in defense against infection through the modulation of innate immune cell function (Spek et al., 2017). Changes in the concentrations of serum thyroxine (T 4) and tri-iodothyronine (T 3) of sheep in seasonal heat and cold stress have already been investigated (Dhanda et al., 2001). Circadian variation in thyroid hormones levels have also been reported in domestic animals (Nazifi et al., 2008).