Vitamin E and Selenium on dairy cattle

The changing trends in animal production require the owner/manager to become more efficient in all aspects of the production cycle. Major contributors to economic returns include reproduction and nutritional management of the herd. While both of these issues are important in their own right, recent data indicate substantial interrelationships between them. To maintain high milk output cows should give birth at shortest possible intervals, which means that there is a very tight schedule, taking account of postpartum uterine involution, anoestrus, successful conception rates and duration of pregnancy in the cow. The time of rebreeding may coincide with a period of high milk production and possibly with a period of negative energy balance. These nutritional stresses can affect the reproductive system and may be manifested as delayed return to cyclicity and failure to become pregnant. Nutrition influences ruminant fertility directly by the supply of specific nutrients required for the processes of oocyte and spermatozoa development, ovulation, fertilization, embryo survival and the establishment of pregnancy. It also influences fertility indirectly through its impact on the circulating concentrations of the hormones and other nutrient-sensitive metabolites that are required for the success of these processes. The impact of trace minerals in this context needs no exaggeration. The antioxidant system of living body safeguards the incidence of aforesaid abnormalities.

Antioxidant and Oxidative Damage

Normal cell processes, environmental insults, and inflammatory responses produce compounds called reactive oxygen species or free radicals. Environmental insults include solar radiation, certain mycotoxins, nitrates, and a host of other toxic compounds. The major free radicals found in biological systems are superoxide, hydrogen peroxides, hydroxyl radical, and fatty acid radicals. Hydrogen peroxide is found primarily in the cytosol of cells and fatty radicals are found primarily in cell membranes. Superoxide and hydroxyl radicals can be found in both cell components. Because free radicals are extremely toxic to the cells, the body has developed a sophisticated antioxidant system (Table-1).

Table 1: Antioxidant systems of mammalian cells.

Role of Vitamin E and Selenium in Bovine Fertility

Male fertility and conception in bovines

Sperm motility, sperm membrane integrity in female reproductive tract plays a vital role in increasing conception rates in cows. In this context it can be said that beneficial effects of ‘supra-nutritional’ supplementary trace minerals (Zn, Co and Se) on sperm motility, percentage of live sperm and sperm membrane integrity in bovines have been observed by Kendall et al. (2000). These benefits, which were accompanied by an improved antioxidant status in the form of increased concentrations of glutathione peroxidase in seminal plasma, were attributed to selenium. A beneficial effect of selenium supplementation (50 mg as barium selenate by S.C. injection) of bovines on the viability and motility of their semen has also been observed by Anderson et al. (1996). Interestingly the beneficial effect in terms of the proportion of normal sperm was more pronounced following freezing and thawing than in fresh semen.

In bulls, significant reductions with age in their sperm concentrations of the polyunsaturated fatty acids, arachidonic 20:4n-6 and docosahexaenoic 22:6n-3, along with an associated reduction in the antioxidant enzyme systems in their seminal plasma (Kelso et al., 1997) have stimulated commercial interest in the use of dietary fish oil supplements and higher inclusion rates for the antioxidant, Vitamin E, to improve fertility. These fatty acids are important for sperm membrane integrity, sperm motility and viability, as well as cold sensitivity. Where there are known adverse effects on sperm production and quality caused by dietary ingredients such as cottonseed which contains the toxic polyphenolic pigment, gossypol, there is evidence from studies with bulls that these can be reversed by feeding 4000 IU per day of Vitamin E (Velasquez-Pereira et al., 1998). Amongst other mechanisms this protection by Vitamin E may be through the prevention of lipid-membrane damage (antioxidant mechanism).


Effect on the oocyte

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 oocyte.

Effect on embryo development and survival

                                                                           Figure 1
                                                                   J. J. Robinson et al.



As a result of stimulating effect on follicle growth (Fig-1) improved preovulatory nutrition increases the size of the ovulatory follicle and the progesterone-secreting ability of the resulting corpus luteum. However, following ovulation high plane feeding can suppress blood progesterone concentrations to levels that compromise embryo survival (Robinson et al., 2002a). In the more controlled feeding systems applied to dairy cows dietary inclusions of calcium soaps of saturated fatty acids which enhance progesterone through increased cholesterol provision (Staples et al., 1998) are easily implemented. However, with growing interest in the use of dietary polyunsaturated fatty acids (PUFA) to increase the unsaturated fatty acid content of milk for improved human health, research is now focused on the effect of dietary PUFA supplementation on dairy cow fertility. However linoleic acid supplementation reduced early luteal progesterone concentrations despite there being a larger dominant follicle and higher IGF-1 and cholesterol concentrations. Care should thus be taken lest some fatty acid-rich supplements compromise embryo survival. This concern is also relevant at the earliest stages of development because, on the basis of in vitro research findings, bovine embryos are sensitive to the adverse effects of fatty acid accumulation unless given adequate antioxidant protection (Reis et al., 2003).


Involvement of various micronutrients in embryo development and survival is shown in below:

                                                                            Figure 2
                                                        Underwood, E. J. shuttle, 1999



Thus it is observed that there is an overwhelming impact of trace minerals and vitamin E on bovine reproduction. Following table shows the direct and indirect effect of selenium on bovine reproduction.

Table 2:

Effect of complexed trace minerals (Zn, Cu, Mn, Se) on bovine reproduction

Marginally mineral deficient animals will abort or calves will be weak and unable to stand or suckle. Research indicates that selenium supplementation reduce the incidence of retained placenta, cystic ovary, mastitis and metritis. In addition cattle that maintain adequate blood selenium levels have reduced incidence of abortion, stillbirths and periparturient recumbency. Compromised selenium status has also been associated with poor uterine involution, and weak or silent heats. Following figure compares the days to conception and conception rates with and without complexed trace mineral supplementation.


DAYS TO CONCEPTION AND CONCEPTION RATES (%) @150d POSTPARTUM OF CATTLE

                                                                                     Figure 3
                                                                               Uchida et al, 2001

Recommendation

Selenium

Essentially all dairy animals should be fed the maximum allowable amount of supplemental selenium (current FDA regulation is 0.3 ppm). Potential benefits are reduced prevalence of retained fetal membranes, reduced abortion rates, increased conception rates and embryo quality. Diets fed to animal at all stages of life (calves, heifers, and lactating and dry cows) should be supplemented with 0.3 ppm selenium. Often heifers are not supplemented properly and are in marginal selenium status when they calve. Sodium selenite and sodium selenite are two approved sources of supplemental selenium for animal diets. Limited data suggests that the selenate may have greater bioavailability than selenite (FDA, 1987). In most situations, feeding 0.3 ppm pro vides adequate selenium, but occasionally that amount is not adequate. Certain conditions (high sulfate in the feed or water, excessive dietary copper, zinc, or iron, and diets with very high or very low concentrations of calcium) reduce the availability of selenium or increase its requirement.


Vitamin E

Most concentrate feeds contain very little vitamin E. Raw soybeans can be a good source of vitamin E, but roasting destroys most of the vitamin E. Fresh green forage is an excellent source of vitamin E and may contain more than 100 IU /lb. of dry matter. Numerous research studies have shown that NRC recommendation for that vitamin E typically exceeds 7IU/lb of dry matter. Based on current data, it is recommended that all dry cows not consuming fresh forage be fed 1000 IU/day of supplemental vitamin E. Researchers think that lactating cows should be fed about 500 IU/day of supplemental vitamin E when fed stored forages. If cows are consuming at least 25% of their diet as pasture, supplemental vitamin E is probably not needed. When cows were in marginal selenium status, very positive results were obtained when dry cows within 2 weeks of calving were fed 4000 IU/day of supplemental vitamin E. No positive results were found when high levels of vitamin E were fed to peripartum cows that were adequate in selenium. If adequate blood concentrations of selenium cannot be obtained because of interfering compounds, extra vitamin E supplementation during the peripartum period may be beneficial.

Conclusion

The function of trace minerals including selenium and vitamin E in reproduction and overall animal performance is of considerable economic concern. Supplemental vitamin E and selenium improve immune function of dairy cattle, especially during the peripartum period. An inadequate intake of selenium and vitamin E is related with an increased incidence of retained fetal membranes, mammary gland infections, and abortion. While gross or major deficiencies may not be seen, lesser problems still may be serious in nature. Meeting the needs of vitamin E and selenium along with other trace minerals requires knowledge of animal requirements. Additionally those factors that affect the availability of the needed minerals must also be considered. Aforesaid nutrients on long term basis are required to maintain normal cellular activity, reproductive function, growth development, mammary and claw health. Improving overall nutrient status by feeding highly bioavailable trace minerals , such as complexed minerals (Zn, Se, Cu, Mn), is one way livestock producer can ensure that their cattle have adequate trace mineral status to help maximize health, fertility and productivity.


References

Underwood, E.J., Suttle, N.F., 1999. The Mineral Nutrition of Livestock, 3rd ed. CAB International, Wallingford, UK, 614 pp.

Kendall, N.R., McMullen, S., Green, A., Rodway, R.G., 2000. The effect of zinc, cobalt and selenium soluble glass bolus on trace element status and semen quality of ram lambs. Anim. Reprod. Sci. 62, 277–283.

Anderson, J.M.L., Ap Dewi, I., Axford, R.F.E., 1996. The effect of selenium supplementation on fresh and frozen ram semen. Anim. Sci. 62, 672.

Kelso, K.A., Redpath, A., Noble, R.C., Speake, B.K., 1997. Lipid and antioxidant changes in spermatozoa and seminal plasma throughout the reproductive period of bulls. J. Reprod. Fert. 109, 1–6.

Rooke, J.A., Shao, C.-C., Speake, B.K., 2001. Effects of feeding tuna oil on the lipid composition of pig spermatozoa and in vitro characteristics of semen. Reproduction 121, 315–322.

Velasquez-Pereira, J., Chenoweth, P.J., McDowell, L.R., Risco, C.A., Staples, C.A., Prichard, D., Martin, F.G., Calhoun, M.C., Williams, S.N.,Wilkinson, N.S., 1998. Reproductive effects of feeding gossypol and VitaminE to bulls. J. Anim. Sci. 76, 2894–2904.

Robinson, J.J., Rooke, J.A., McEvoy, T.G., 2002a. Nutrition for conception and pregnancy. In: Freer, M., Dove, H. (Eds.), Sheep Nutrition. CAB International, Wallingford, UK, pp. 189–211.

FDA-1987. Food Additives Permitted in Feeds and Drinking Water of Animals: Selen ium. Federal Register 52:10887 (Monday, April 6), 1987.

Staples, C.R., Burke, J.M., Thatcher, W.W., 1998. Influence of supplemental fats on reproductive tissues and performance of lactating cows. J. Dairy Sci. 81, 856–871.

Reis, A., Rooke, J.A., McCallum, G.J., Staines, M.E., Ewen, M., Lomax, M.A., McEvoy, T.G., 2003. Consequences of exposure to serum, with or without Vitamin E supplementation, in terms of the fatty acid content and viability of bovine blastocysts produced in vitro. Reprod. Fert. Dev. 15, 275–284.

Uchida, K, P. mandevbu, C. S. Ballard, C. J. Sniffen and M. P. Carter. 2001. Anim. Feed. Sci. Technol. 93:191-203.