Review/Oorsig Volume 23, Issue 01 - Page 8

Oorsig/Review their function which can lead to sperm damage and male infertility. Reactive oxygen species are produced by living organisms as a result of: • • Normal cellular processes (sperm production), inflammatory events (disease conditions), stressful events (weaning, mating). Environmental factors (heat stress, drought). Controlled quantities (low to moderate concentrations) of ROS have been shown to be essential for sperm physiological processes that are necessary to ensure fertilization. The maintenance of suitable ROS levels is therefore essential for adequate sperm functionality to ensure fertilization. Regulating and reducing ROS to physiological levels, is thus critical for cell viability, organ function and early embryo development. Oxidative stress in the reproductive system is thought to have an effect on the fertilizing ability of sperm. Poor sperm motility, rather than low sperm concentration, is most often the cause of male infertility. Therefore, an antioxidant that reduces oxidative stress and improves sperm motility could be useful in the management of male infertility. Trace minerals play an important role as co- enzymes in various metabolic processes, antioxidants, immune responses and minimizing the effect of stress in ruminants by supporting the antioxidant defence mechanisms designed to keep the reactive oxygen species (ROS) in balance. Oxidants can either be from endogenous sources of ROS or from exogenous sources of oxidants. Endogenous sources of ROS Two of the main factors contributing to ROS accumulation, are the absence of endogenous defence mechanism and environmental conditions that can lead to generation of OS. The fluctuations in ROS might be due to transient subclinical infection, transient abnormalities in spermatogenesis or periodic presence of abnormal spermatozoa in semen. Reactive oxygen species are produced from molecular oxygen as a result of normal cellular metabolism or during phagocytosis and destruction of microorganisms by neutrophils and can be divided into 2 groups: 8 1. Free radical: Molecules containing one or more unpaired electrons (and thus giving reactivity to the molecule) are called free radicals and they are able to cause DNA mutations, as seen with hypochlorous acid (HOCI) generated by phagocytes. 2. Non-radicals: When 2 free radicals share their unpaired electrons, non-radicals forms are created. ROS is produced by both sperm and leukocytes contaminating seminal fluid. There are four major ROS that are of physiological significance by adversely affecting sperm motility and impairing fertilization ability, namely: • • • • Superoxide anion (O 2 ), Hydroxyl radical (OH), Hydrogen peroxide (H 2 O 2 ) Hypochlorite radical (OHCl). Previous research has demonstrated that high hydrogen peroxide concentrations reduces bull sperm motility in vitro and may impair fertilization and embryo development. In bovine semen ROS are generated primarily by dead spermatozoa while leukocytes, particularly neutrophils and macrophages, as well as immature spermatozoa are the two main sources of ROS that causes sperm dysfunction. Exogenous sources of oxidants Exogenous sources like smoke, dust, heavy metals and heat stress lead to the release of inflammatory mediators as well as accumulation of neutrophils and macrophages which increase the oxidative injury. Chauhan et al indicated that heat stress impairs animal performance and it has been implicated in promoting OS. Therefore a robust antioxidant network capable of preventing oxidative damage of biological molecules holds promise for improving the health and performance of animals during heat stress. Antioxidant enzymes, such as glutathione peroxidase (GSH-Px) can be inhibited by various exogenous sources. Low levels of Zinc (Zn), which serves as a cofactor for many of these enzymes, can lead to inactivation of such enzymes. Antioxidants The role of chemical elements in natural antioxidant structures has recently attracted much scientific interest. The body is equipped