Minerals and vitamins play an important role in reproduction and productivity of animals through their involvement in various enzyme systems. Reproductive performance of farm animals depends on adequate balanced levels of vitamins and essential peroxides minerals due to their important roles in cellular metabolism, maintenance and growth (Shweta and Bhavava, 2009) to water (Zini et al. 2000). Also, these Production nutrients have specific roles and requirements in reproductive tissues (Agarwal et al. 2006). Vitamin E molecules constitute a major part of the antioxidant system as they act as membranes protectant to maintain the integrity of phospholipids against oxidative damage (Greco et al. 2005).The imbalance and/or deficiency of minerals and vitamins leads to inactive ovaries and repeat breeding in dairy animals (Rogers 1992). Anoestrus is one of the most important functional ovarian disorders in livestock affecting adversely the economics of dairy animals by delaying age of first calving and calving interval. Causes of anoestrus have been attributed to many factors viz. nutritional deficiency, seasonal changes, environmental and lactation stress, ageing and pathological disorders ultimately leading to endocrine disturbances.  Though some of the research reports have conflicting opinions of the role of Vitamin E and selenium in anoestrus and conception in farm animals, yet majority of the scientific information is supporting the positive influence of Se and vitamin E on reproductive disorders (Hidiroglou 1979; McDowell 1992). Selenium was found to be an essential dietary nutrient in 1957 (Schwarz and Foltz 1957). Selenium deficiency is responsible for a number of specific degenerative diseases in livestock; and it is increasingly clear that adequate selenium is necessary for basic processes such as growth and reproduction (Levander 1986; Oldfield 1997). In animals, Selenium has long been associated with a wide range of practical and costly problems including both male and female fertility.

Vitamin E

Vitamin E is very important antioxidant essential for growth, reproduction, prevention of various diseases and integrity of tissues (Quereshi et al 1997). The NRC requirement for selenium is 0.1 mg/kg but a more practical level is 0.2mg/kg. Deficiency symptoms include white muscle disease, loss of condition, retained placenta, reproductive disorders. Vitamin E is a biological antioxidant which is essential for optimum nutrition. a tocopherol, the major component of vitamin E, is the most important free radical scavenger. Production of free radicals could represent a source of infertility, because ovarian steroidogenic tissue (Crowe 2008), spermatozoa (Sanocka and Kurpisz 2004) and preimplantation embryos (Fujitani 1997) are sensitive to free radicals damage. In some studies, administration of carotene or vitamin E and selenium (Ahmed et al 2010) improved fertility of bovine, while in other studies, providing high amount of these antioxidants showed no beneficial effects on fertility (Stowe yet al 1988). Supplementation bovine, while in other studies, providing high amount of of chain breaking antioxidants in the nutrition of high producing cows has been shown to be essential for optimizing production (Miller and Madsen 1994). A reduction in retained placenta follwing treatmnt of cows in late pregnancy with Vit E and Se (Trinder Hall and Renton 1973).

Selenium

The function of selenium has only recently been revealed which functions through glutathione peroxidase (active in cytosol), which reduces hydrogen peroxide and other organic peroxides to less damaging end products. Selenium deficiencies have been reported to suppress the immune response in various species (Reffett et al 1988) which may also contribute indirectly to the reproductive inefficiencies. Selenium along with Vitamin E function as preventive and chain breaking anti oxidant, and inactivates peroxidise formed during cell metabolic process. (Hine 1992). Commonly recorded selenium responsive reproductive disorders of cattle are retained placenta, abortion, still birth, irregular estrous cycle, early embryonic mortality, cystic ovaries (Randhawa and Randhawa 1994,) silent heats and poor fertilization (Corah and Ives 1991). Reproductive performance may be reduced with increased number of services needed per conception and a retained fetal membrane in sub clinical selenium deficiency and this may be due to the impaired functioning of neutrofils (Goff 2005). The NRC beef cattle publication (1984) recommends 0.20 ppm selenium in the diet and selenium can be included in beef cattle diets up to 0.3 ppm which is the maximum legal limits in the United States (NRC 1996).

Role of Vitamin E and Selenium in oxidative Damage

Research into methods of improving the efficiency of ruminant multiple ovulation and embryo transfer programmes and, more recently, in vitro systems of embryo production from oocytes obtained by aspirating ovarian follicles is providing new information on the impact of oocyte-donor nutrition on oocyte quality. Besides other factors of improving the quality of oocytes and thereby fertility of cows, impact of antioxidants is overwhelming. The beneficial role of vitamin E and selenium in this context is via antioxidant mechanism. It works simultaneously, keeps biological membrane intact and assures quality of oocyt. During parturition and after heavy milk yield causes stress to the animal. In stress condition, normal cell processes, environmental insults, and inflammatory responses produce compounds called reactive oxygen species or free radicals.  Vitamin E and to a lesser extent carotene reacts with fatty acid radicals and stops the chain reaction. Free radicals can react with nucleic acids causing mutations, they can react with enzymes and render them inactive, and they can react with fatty acids in membranes causing membrane instability.  Free radicals can eventually kill cells and damage tissues.  Systems for protection against reactive oxygen metabolites pathway (Miller et al 1993) is given below.

This pathway may be more active when it is deficient in Se or vitamin E. The resulting destruction of glutathione increases consumption of reducing equivalents, thus competing with other metabolic pathways that depended on NADPH. Chain-breaking antioxidants interrupt peroxicative chains initiated by reactive oxygen metabolites that escaped enzymatic degradation. Vitamin E serves as a chain-breaking antioxidant by reacting directly with free radicals. Although vitamin E is consumed when free radicals are quenched.

Animals require adequate levels of both Se and vitamin E because of their interrelated functions. The amount of either needed by the animal depends on the availability of the other as illustrated in Figure 2.

Role in Anoestrus and Conception

The relationship of selenium to male fertility involves three different factors; anti-oxidant activity, sperm structure and the development of the fertile cell in the testis (Marin-Guzman et al 1997). Selenium deficiency has been linked to testicular degeneration, low sperm count and reduced motility. In ruminants, reproductive disorders for Se deficiency are generally manifested by weak or silent heat periods, delayed conception, poor fertilization, cystic ovaries, reduced sperm motility, decreased uterine motility, mastitis and retained fetal membrane. A selanoprotein has been identified which is a major component of the sperm cell capsule or tail mid-piece and there is association between sperm cell motility and dietary selenium (Arthur 1997). The testis has a high priority for selenium and is having highest selenium concentration. Spermatozoa contain high concentration of polyunsaturated fatty acids (PUFA) in phospholipids, an important risk factor for peroxidative damage to spermatozoa membranes and are considered to be the cause of male sub fertility. Besides a number of functions, selenium with vitamin E play an important role in reproductive processes of both males and females of livestock animals. High concentrations of selenium in testes and epididymides indicates its importance for the processes of production and maturation of spermatozoa The  reports on studies performed on boars have demonstrated that an addition of 0.5 ppm selenium to feed rations applied in young boar raising significantly and positively influenced both semen quality (sperm motility, concentration, and morphology) and the conception rate. E in conjunction with selenium has an essential role in the protection of spermatozoan lipids against peroxidation (Surai 2000).

Majority of the clinical trials on Se and vitamin E responsive reproductive disorders have indicated existence of positive interaction between Se intake and availability of vitamin E. Deficiency has been found to decrease the fertilization rate and causes in retained placenta (Robinson 1986). Vitamine E is promoting release of FSH, ACTH and LH. Supplemental vitamin E and selenium reduced the incidence of anoestrus or subestrus in cattle (Jukola et al. 1996). Selenium could also influence uterine involution and postpartum ovarian activity through its postulated effect on immune function, uterine contractility, thyroid hormone metabolism and synthesis of prostaglandins ( Wichtel et al. 1996). Supplementation of vitamin E along with selenium for anoestrus buffalo resulted increase erythrocytic glutathione peroxidase activity and lipid peroxidation and improve the antioxidant status as well as reproductive performance (Nayyer et al. 2005). Harrison et al (1984) reported that Se status of the dairy animal at calving has an effect on uterine health and ovarian function during the early postpartum period. He also reported also recorded that the incidence of cystic ovaries and metritis was significantly reduced in Se administered group as compared to untreated controls.  Deficiency of Se during the prepartum period has a continuing effect and predisposes the dairy animal to increased risk of mettritis and Cystic ovarian disease in the subsequent postpartum period. Providing supplemental vitamin E during the prepartum period appears to be an important factor in the efficacy of Se treatment for prevention of RP in dairy cattle. A study with beef heifers in 1991 found a high correlation between serum concentrations of α-tocopherol and pregnancy rate. Few positive relationships between plasma (or serum) α-tocopherol concentrations and measures of mammary gland health have been found when concentrations are greater than about 4 mg/liter. Based on these data, plasma concentration of α–tocopherol might be useful in assessing vitamin E status of dairy and beef cattle, and current data suggest the concentrations should exceed 3 to 3.5 mg/liter at calving. In sub-clinical Se deficiency, performance may be reduced with slower body weight gains and lowered reproduction associated with an increased number of services needed per conception. Abortion and infertility have also been commonly recorded in dairy animals affected with subacute to chronic form of selenosis (Rogers et al. 1990)

Recommended Concentration in Total Ration Dry Matter

Trace Minerals

Iron                                          50 ppm

Cobalt                                      0.10 ppm

Copper                                     10 ppm

Manganese                               40 ppm

Zinc                                         40 ppm

Iodine                                      0.60 ppm

Selenium                                  0.30 ppm

Vitamins

Vitamin A                                  1450 IU/lb

Vitamin D                                  450 IU/lb

Vitamin E                                  7 IU/lb

Taken from: Nutrient Requirements for Dairy Cattle. 6th Revised Edition. 1989. National Academy Press.

Conclusion

Relationship between reproductive function and Selenium and vitamin E has been well established. Though the mechanism of selenium and vitamin E in reproduction interaction is not fully understood but they act directly on the gonads and other reproductive organs. Reproductive efficiency is influenced by many factors including plane of nutrition, rate of weight gain, level of stress and level of milk production. Improvement in dietary nutrition with Selenium and Vitamin E of dairy cattle should be part of an effective programme to improve reproductive performance, as these play vital roles in reproduction.

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