The Effect of Selenium and Vitamin E Injection Times in Late Pregnant Ewes on Thyroid Hormones Metabolism, Ewe's Blood Biochemical Parameters and Their Lambs Performance after Birth

Introduction Selenium and vitamin E are of the micronutrients that may have an impact on immune functions and health. They protect biological membranes from oxidative damage by acting as scavengers of reactive oxygen species (ROS). Metabolic functions of vitamin E are closely linked to the selenium-containing enzyme glutathione peroxidase (GPx). Optimal serum concentrations of vitamin E are difficult to maintain in the period around lambing due to an increased need for antioxidants during this time. In addition, selenium levels of many soil of Iran are low; this makes the situation gets worse. Therefore, excessive accumulations of ROS affects placental development and function both in early pregnancy and towards lambing, and may subsequently impact both the fetus and dam. Additionally, selenium is also essential for the conversion of T4 to T3, as deiodinase enzymes (those enzymes that remove iodine atoms from T4 during conversion) are selenium-dependent. T3 is the active form of thyroid hormone, and low T3 can cause hypothyroid symptoms. Therefore the aim of this experiment was to investigate the effect of selenium and vitamin E injection times in late pregnant ewes on thyroid hormones metabolism, ewe's blood biochemical parameters and their lambs performance after birth. Material and Methods To perform this experiment, 9 weeks before parturition, 24 head pregnant ewes of Mehraban breed were allocated to 4 treatments (n=6). Treatments included: Tr1) Did not received any supplement until end of the experiment (Control); Tr2) Received one time an injectable form of vitamin E+selenium (E+Se) at 9 week before parturition; Tr3) Received two times E+Se injection at 9 and 6 week before parturition; Tr4) Received three times E+Se injection at 9 and 6 weeks before and 1 week after parturition. During each time of injection, 5 ml E+Se per ewe was injected that each ml contains 0.5mg Se as sodium selenite and 50 IU vitamin E as DL-alpha tocopheryl. Before each time of injection, blood samples of all ewes were collected by jagular vein. Hormones concentration of T4 and T3, lipid parameters such as triglyceride (TG), total cholesterol (CHOL), VLDL, LDL, HDL and also aspartate transaminase (AST), creatine phosphokinase (CPK) and Iron (Fe), copper (Cu) and Zinc (Zn) elements concentrations in serum were determined 6 week before and 1 and 2 week after parturition. Lambs performance parameters were recorded until 45 days of age.Results and Discussion According to results of this experiment, 6 weeks before parturition, T4 concentration reduced and T3 to T4 ratio and also Zn concentration increased significantly (P