Redox Status and Hematological Variables in Melatonin-Treated Ewes during Early Pregnancy under Heat Stress

Abstract

The preovulatory follicles and preimplantation stage embryos are found to be rather sensitive to heat stress due to their low potential for scavenging reactive oxygen species (ROS). The aim of the present study was to assess the impact of melatonin administration on redox status and hematological variables during the preovulatory period and early stages of embryogenesis in heat-stressed ewes in vivo. Forty Karagouniko-breed ewes were divided in two groups, the melatonin (M, n = 20) group and control (C, n = 20) one. All animals were subjected to heat stress throughout the study, which lasted forty days (D0 to D40). In M group, melatonin implants were administered on D0. Then, oestrous synchronization was applied (D19-D33). On D34, six rams were introduced into the ewe flock for mating. Ultrasonographic examination was conducted on D73 for pregnancy diagnosis. The temperature humidity index (THI), the rectal temperature (RT), and the number of breaths per minute (BR) were evaluated twice daily. Redox biomarkers, namely total antioxidant capacity (TAC), reduced glutathione (GSH), and thiobarbituric acid reactive substances (TBARS), were assayed in blood samples collected on D0, D33, and D40. In addition, packed cell volume (PCV), white blood cells (WBCs), leukocyte differential count, and cortisol assessment were conducted in blood samples on D33 and D40. The results indicated improved fertility rate and mean number of lambs born per ewe due to improved redox status (p < 0.05) in ewes that received melatonin implants 34 days approximately before the onset of oestrus. The PCV decreased in both groups between the two time-points (p < 0.05). However, the NEU/LYMPH ratio decreased (p < 0.05) only in group M. The low cortisol levels and the decreased NEU/LYMPH ratio in both groups support the hypothesis that ewes of the indigenous Karagouniko breed may exhibit adaptation to environmental thermal stress. The administration of melatonin as an antioxidant regime may improve the reproductive competence of heat stressed ewes and may also enhance their ability to adapt at high ambient temperatures.

The effect of exogenous melatonin administration before superovulation on embryo yield in Assaf ewes

“…In domestic mammals, melatonin has been shown to regulate gene expression required for the synthesis of antioxidants such as GSH‐Px and SOD, and to increase mRNA synthesis (Mayo et al., 2002). It has been reported that reproductive potential can be increased as a result of raised activity of GSH‐Px and SOD enzymes, alone or in combination, in mammalian oocytes and/or embryos (Bouroutzika et al., 2022; Shi et al., 2009; Song et al., 2019; Su et al., 2015; Tamura et al., 2012). It has been reported that melatonin (18 mg) administered 8 days prior to superovulation in prepubertal lambs increases SOD and GSH‐Px activities in cumulus cells, reaching higher concentrations than the control group and causing less ROS accumulation.…”

Melatonin increased antioxidant capacity to ameliorate growth retardation and intestinal epithelial barrier dysfunction in diquat‐challenged piglets

“…Previous studies showed that melatonin has a good antioxidant effect, and is a free radical scavenger and broad-spectrum antioxidant. 15,16 Melatonin can clear free radicals and increase antioxidant enzyme activity. 17,18 Previously studies showed that melatonin upregulated the expression of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD).…”

“…The concentration of melatonin varies widely in the gastrointestinal tract. Previous studies showed that melatonin has a good antioxidant effect, and is a free radical scavenger and broad‐spectrum antioxidant 15,16 . Melatonin can clear free radicals and increase antioxidant enzyme activity 17,18 .…”