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.

This study evaluated the effects of maternal supplementation with rumen-protected methionine (RPM), alone or combined with rumen-protected choline (RPC) and betaine (RPB), during the periconceptional and prepartum periods on reproductive outcomes and offspring performance in Chios ewes. One hundred synchronized ewes were assigned to three groups—control (no supplementation), M (5.50 g RPM/day), and MCB (3.50 g RPM, 1.60 g RPC, 0.49 g RPB/day)—from day −14 to +14 relative to mating. Blood was collected on days −14, 0, and +14 for ABTS (2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), ferric-reducing ability (FRAP), and malondialdehyde (MDA), on days 18 and 21 for progesterone, and on day 26 for pregnancy-associated glycoprotein (PAG) detection. Thirty days before and up to lambing, the ewes were further divided into C-C, C-M, C-MCB, M-M, M-C, MCB-MCB, and MCB-C subgroups. Embryonic loss did not differ between groups. FRAP was higher (p < 0.001) in MCB ewes, and ABTS was lower (p < 0.05) in M ewes, in the periconceptional period. Offspring in the C-M, C-MCB, M-M, M-C, and MCB-MCB groups had higher birth weights (p < 0.01), along with increased MDA levels (p < 0.05). The results suggest that maternal methyl donor supplementation during early and/or late gestation enhances antioxidant status, supports embryonic development, and increases birth weight.