Mitigating Heat Stress Effects:Impact of Melatonin on Blood Cell Morphology in Ewes

Sheep exposed to excessive heat can suffer various adverse effects, particularly on their hematological system, including blood cell integrity and function. Melatonin has a protective role by mediating antioxidant pathways and acts as a regulator on apoptosis. The objective of this study was to evaluate the impact of heat stress on blood cell morphology and hematological variables in ewes and whether melatonin administration could mitigate it. Seventy-four ewes of Karagouniko breed participated in the study and were divided into three groups; the heat stress-melatonin group (HM, n = 20) and the heat stress-control group (HC, n = 20) and the control group (C, n=34). The heat stress-melatonin group as well as the heat-stress control group were evaluated during the summer period, whereas the control group was evaluated in autumn. All the animals in the HM and HC groups experienced heat stress, while those in group C did not. Following the administration of melatonin implants to the HM group (D0), blood samples were collected forty days later (D40) as well as from those in HC and C group. Blood smears were prepared and Giemsa stained, and thereafter, the packed cell volume (PCV), hemoglobin (Hgb), and mean corpuscular hemoglobin concentrations (MCHC) were estimated in all blood samples. Lower values of MCHC (P<0.05) were observed in the HC group compared to the HM or C group. The percentage of ewes exhibiting echinocytes, polychromatophils, red blood cell (RBC) and platelet (PLT) aggregates was significantly higher (P<0.05) in the HC group than in the HM or C group. This study represents the first report documenting blood cell morphological changes and highlights the potential benefits of melatonin supplementation in preserving blood cell integrity under heat-stress conditions.