Oxidative stress is one of the major causes of the decrease in viability and development of embryo
1. Embryo is highly sensitive to injury to oxidant molecules because of its low antioxidant capacity
2. In the various researchs, studies focused on studying antioxidant strategies to prevent oxidative stress induced damage to gametes and developing embryos
3. It is known that vitamin E (vit E) and selenium (Se) are powerful free-radical scavenger and antioxidants. Vit E prevents the oxidative chain from proliferating prior to the alteration of neighboring molecules by being oxidized into harmless compounds
4,5. Selenium is important in inhibiting nitric oxide production in cells
6 and is an essential element of several enzyme systems, including glutathione peroxidase (GSH-Px) and deiodinase
7. These enzymes have been shown to be important in embryonic development, through their antioxidant functions and regulatory effects on metabolic rate
8. In addition to, plasma GSH-Px activity is assumed to be indicative of oxidative stress
9. Vit E and Se are capable of improving the developmental capacity of bovine embryos in vitro
10,11. Vit E and Se may suppress these oxidants. Several studies have shown that administration of Se, vit E or vit E and Se in combination resulted in higher pregnancy rates
12-14. However, other studies have shown little or no beneficial effect of administration of vit E and/or Se
15-17. Oxidative stress and maternal low blood progesterone levels during early embryonic development are a major cause of decreased pregnancy rate in dairy cows. Vierk et al.
18 suggested that luteolysis of the corpus luteum is due to accumulation of oxidative species. Circulating progesterone concentrations are critical for maintenance of pregnancy. It has been suggested that some of early pregnancy losses in livestock may be due to insufficient circulating progesterone concentrations
19. Hence, use of appropriate antioxidants can help to improve conception rate by preventing accumulation of oxidative species during early embryonic development in dairy cows. However, whether vit E and Se posses similar benefits on the conception rate in cows has yet to be determined.
The objective of this study was to investigate the effect of a single subcutaneous injection of vit E and Se administered just before ovsynch on erythrocyte GSH-Px and superoxide dismutase (SOD) activities and plasma progesterone levels and pregnancy rates of lactating dairy cows.