Introduction

Selenium has attracted much attention recently in animal and human nutrition. Even though selenium in excess is toxic, in trace amounts it exerts various beneficial effects in vivo. Selenium supplementation was found to improve the growth and muscle development. Selenium influences the immune response by the activation of phagocytosis, increased antibody production and enhanced lymphocyte proliferation. Supplementation of selenium had increased the blood globulin level indicating the improved immunity status in male buffalo calves of 8 to 9 months of age (Mudgal et al. 2008).

Selenium is an effective antioxidant in animal body being the key component in the antioxidant enzyme, glutathione peroxidase (GSH-Px) which protects cells and unsaturated fatty acids in cell membranes from damage by oxidizing materials. Selenium dependent enzymes deiodinases are responsible for the formation of biologically active thyroid hormone T₃ from T₄, deficiency of which affects the production performance of the animal. Selenium has been approved as a feed additive for cattle ration since 1979, first at an added level of 0.1 mg/kg of DM (FDA, 1979) and at 0.3 mg/kg of DM (FDA, 1987).

Growth

Selenium plays an important role in the formation of thyroid hormones. Enzyme 5 iodothyronine deiodinase is a selenium dependent enzyme, which helps in the activation of T₄ (tetra iodothyronine). Selenium influences the growth performance through the formation and activation of thyroid hormones. Selenium and Vitamin E functions are inter dependent. Selenium and Vitamin E, both are excellent anti oxidants as they form part of the major antioxidant enzyme glutathione peroxidase. Selenium deficiency can be partially compensated by Vitamin E supplementation. So the deficiency of Selenium and Vitamin E results in thyroid malfunction which inturn results in retarded growth. Selenium requirement for calves is 100 µg/kg DM and Vitamin E about 40-60 IU (NRC, 2001).

Gleed et al. (1983) from his studies on the effects of selenium and copper supplementation on the growth of beef steers reported that by supplementing 0.15 mg selenium/kg body weight increased growth rate by 0.041 and 0.060 kg/day respectively in two experiments. Phillips et al. (1989) reported increased weight gain by selenium supplementation in suckling beef calves in the 90 to 120 days period of their test but gains were not significantly different for the whole 120 days period. Tsai and Bukas (2003) also observed 14.1 per cent increase in the body weight gain of calves aged from two to three months when supplemented with 0.2 mg sodium selenite/kg feed. Similarly, Reiss et al. (2008) also observed higher weight gain in twelve month old Nellore calves when supplemented with 5.4 mg of selenium/ animal/ day.

Selenium supplementation can be done through different routes. Studies were also done regarding supplementation of selenium through intra ruminal and parenteral routes. Results will be quicker while supplying through parenteral route compared with that of oral route. Wichtel et al. (1996) got higher mean daily body weight gain for Friesian calves on supplementation with selenium as intra ruminal pellets than that of the non supplemented group.

Increased growth response on parenteral supplementation of selenium was reported by different authors. Spears et al. (1986) noticed increased weaning weight in calves when injected with 5.5mg selenium and 75 IU Vitamin E /100 kg body weight at 60 days intervals from first to fifth or seventh month of age when compared with un supplemented calves. Reffett et al. (1986) found that selenium injection at 15 mg/head increased calf weight gains in first fourteen days after weaning. Yuhua et al. (1996) also got similar result in goats. Castellan et al. (1999) obtained higher average daily gain than the control group on parenteral administration of selenium to suckling beef calves at the rate of 0.05 mg/kg within two days of birth and on days 70, 114 and 149.

Selenium is available in inorganic and organic form. Common inorganic forms include Sodium selenite and selenate. Organic form exists as Seleno methionine. The organic source of selenium yeast is more digestible than commonly used inorganic selenium (sodium selenite) (Pagan et al., 1999). Guyot et al. (2007) observed higher growth in calves fed diets with organic selenium (Y-Se) when given at the rate of 0.5 ppm compared to those fed diets containing inorganic selenium as sodium selenite. Lambs fed diet with 0.15 ppm selenium as sodium selenite or organic selenium (Jevsel-101) recorded improved growth rate, humoral immune response and antioxidant status compared to non supplemental control (Kumar et al., 2009) and the effect being higher for organic selenium group than those fed inorganic selenium supplemented diet.

Several works showed no effects of selenium supplementation on growth. Mehdi and Dufrasne (2016) explained that the selenium dependent selenoprotein, 5 iodo thyronine deiodinase is one of the last protein to be affected due to selenium deficiency, which may be the reason for this non effect of Selenium on growth performance. Dietary supplementation of selenium at 0, 0.1 and 1 ppm in Holstein calves of 120 days of age for a period of 28 days by Kincaid et al. (1977) could not observe any significant difference in calf weight gains. Growth studies conducted in sheep and crossbred steers by Ullrey et al. (1977) also could not obtain any significant improvement in average daily gain by dietary supplementation of selenium at 100 and 200 ppb as sodium selenite for six weeks. Ammerman et al. (1980) supplemented selenium at 0.1 or 0.2 ppm as sodium selenite to beef cows and suckling calves along with soybean meal, corn and linseed meal and observed that selenium supplementation did not significantly influence live weight of the cows or birth weight of calves, but had an increasing trend in weaning weight of the calves. Siddons and Mills (1981) tested three basal diets containing 0.05, 0.025, and 0.024 ppm of selenium as sodium selenite on four week old Friesian bull calves and noticed no significant difference in average daily gain during the feeding trial of 36 weeks. When calves were fed skim milk powder based milk replacer containing either 0.2, 1, 3, 5 or 10 ppm selenium added as sodium selenite from 3 to 45 days of age to estimate the lowest amount of dietary selenium that would reduce calf performance and feed utilization by Jenkins and Hidiroglou (1986), only the highest selenium (10 ppm) fed calves showed reduced average daily gain. They also opined that preruminant calves were very tolerant of high inorganic selenium concentration in skim milk powder based milk replacer.

McClure and Mahan (1988) had not observed any effect on the growth rate of growing and finishing lambs received diet with 0.25, 1or 2 ppm of selenium as selenium yeast. When calves were supplemented with sodium selenite, selenium enriched yeast and live yeast culture, Nicholson et al. (1991a) obtained no difference in weight gain due to treatment. Nursing cows when supplemented with 113 g/day of free choice mineral mixture containing 26 ppm selenium as sodium selenite or selenium yeast (selplex), Gunter et al.(2003) noticed no significant improvement in average daily gain of nursing calves. Lawler et al. (2004) also reported that dietary selenium supplementation (2.84ppm) had no effect on the average daily gain of crossbred steer heifers. Slavik et al. (2008) observed no significant increase in weight gain in the calves that were supplemented with both organic and inorganic forms of selenium at the rate of 1mg per head per day. Juniper et al. (2008) noticed no treatment effect on body weight by giving selenium at varying levels (0.15 to 6.63 ppm) as selenium enriched yeast to cattle, calves and lambs. Feeding calves on torula yeast based diet with or without sodium selenite (0.1 to 0.45 ppm selenium) did not influence growth rate and feed intake (Lum et al., 2009). Richards et al. (2011) had given 0.34 ppm of supplemental selenium from selenium yeast for a 130 day finishing period to beef cattle and obtained no improvement in body weight gain.

In calves received 0, 1 or 2 injections of selenium and vitamin E at a dose rate of 0.078 mg and 5.4 IU/ 100 kg respectively during a period of 14 to 56 days of age, Weiss et al. (1983) had not observed any improvement in weight gain in treatment groups. Afzal et al. (1988) had not obtained any significant difference in weight gain when newborn jersey calves and buffalo calves were supplemented with 500mg of vitamin E and 200 µg selenium daily from birth to 30 days of age. Effect of preweaning parenteral supplementation of vitamin E and selenium at the rate of 300 U and 6mg/45 kg body weight to new born calves at 24 to 48 hours and 14 days after birth up to three months of age was studied by Mohri et al. (2005) and observed no significant differences for weight gain from birth to three months compared to un supplemented control. Non significant effect of dietary supplementation of selenium enriched yeast and vitamin E at varying levels on body weight gain was also reported by Skrivanova et al. (2007) in calves. Supplementation of selenium at 0.3 ppm alone or vitamin E at 300 IU/ day plus selenium at 0.3 ppm as sodium selenite had not improved the growth performance and nutrient utilization in male buffalo calves of 10 to 12 months of age (Shinde et al., 2008). Swecker et al. (2008) found no effect on weight gain in weaned beef calves when fed with 0.1 mg of selenium and 0.22 IU vitamin E/kg of body weight.

Immune Response and Health

Relationship between selenium and udder health due to its antioxidant properties are well known. Selenium supplementation can improve humoral and cellular immune responses. Selenium supplementation cause improved expression of natural killer (NK) cells. Phagocytic activity of neutrophils also increases by selenium supplementation.

Glutathione Peroxidase Activity

Siddons and Mills (1981) observed that in calves, the plasma and whole blood activity of GSH-Px was reduced to a minimum level of approximately 15 units/g haemoglobin at 16 weeks in low selenium group where as in the selenium supplemented group, activity increased continuously during the first 22 weeks to a maximum level of approximately 300 units/g haemoglobin. Stabel et al. (1989) from his studies on effect of selenium on GSH-Px and the immune response of stressed calves challenged with Pasteurella hemolytica,noticed a higher GSH-Px activity for selenium supplemented group. The GSH-Px of whole blood was numerically higher in cows fed with selenium fertilized silage than that with inorganic selenium though the differences were not significant (Nicholson et al., 1991b). Gerloff (1992) observed that when selenium was given at 0.3 and 6mg per day, the whole blood GSH-Px increased from 15 mU to 25 mU/mg of haemoglobin. Walsh et al. (1993) noted that erythrocyte GSH-PX activity in calves fed on diets supplemented with selenium increased steadily reaching a plateau of between 250 and 320 IU/g haemoglobin compared to that of erythrocyte GPX activity (55 IU/g Hb) in calves fed on diets low in selenium. Rowntree et al. (2004) also found that dairy cows drenched with 20 mg selenium as sodium selenite weekly once for two months showed significant increase in GSH-Px, the values being 14.91 vs 24.61 EU/g of haemoglobin. Lum et al. (2009) observed that GSH-Px activity was greater for calves fed selenium adequate diet than for selenium deficient calves by 84 days of age. Edward et al. (1985) observed that selenium treated calves showed higher blood GSH-Px concentrations (143 units/g haemoglobin) when compared to non supplemented control. Activities of superoxide dismutase and GSH-Px were significantly increased by selenium supplementation at 0 or 1 ppm level in Liaoning cashmere goats (Qin et al., 2011).

Influence of organic and inorganic selenium supplements on GSH-Px activity was also studied by several authors and organic selenium was found to have higher GSH-Px activity. Significant increase in GSH-Px activities were noticed by Gunter et al. (2003) in calves born to cows supplemented with selenium yeast compared to those fed selenium as sodium selenite. In Belgium blue cows and calves Guyot et al. (2007) obtained higher GSH-Px activity in erythrocytes for 0.5 ppm selenium yeast diet against 0.1 ppm sodium selenite. Beef cattle fed diets supplemented with 6.47 ppm of selenium as selenium yeast showed significant GSH-Px activity of 1283 compared to 844 units per gram haemoglobin in control which received 0.2 ppm selenium diet (Juniper et al., 2008). Kumar et al. (2009) by giving 0.15 ppm of selenium through sodium selenite and organic selenium (Jevsel 101) found increased RBC GSH- Px activity in lambs when fed diets supplemented with 0.15 ppm of selenium as sodium selenite.

But in contradiction to these results Ortman and Pehrson (1997) reported that calves fed diets supplemented with sodium selenite (3mg) and selenium in yeast (0.75 and 3mg) showed similar GSH-Px activity in erythrocytes. Slavik et al. (2008) also reported significantly higher GSH-Px activity in late pregnant beef cows and calves fed diet supplemented with organic and inorganic selenium.

Combinations of selenium and Vitamin E also showed similar results as they work in an interdependent manner. When selenium (5.5 mg) and vitamin E (75 IU) injections were given in calves, Spears et al. (1986) also noticed improved whole blood GSH-Px activity than that of control group. Kennedy et al. (1987) studied the experimental myopathy in vitamin E and selenium depleted calves with and without added dietary polyunsaturated fatty acids as a model for nutritional degenerative myopathy in ruminant cattle and reported high GSH-Px activity in vitamin E-selenium supplemented group with no clinical abnormalities or evidence of myo degeneration.

Immune Response

Highest density of selenium is found in kidney, while it is found in highest amount on muscles. So the first organs to be affected due to selenium deficiency are heart, skeletal muscle and liver (Meschy, 2010). Nutritional muscular dystrophy is a common occurrence due to selenium deficiency. Hidiroglou et al. (1985) found that administration of intraruminal pellets to cows during last three months of pregnancy had reduced the case of nutritional muscular dystrophy in calves. Along with kidney, liver, testis and lungs also store large amount of selenium. Reffett et al. (1988) noticed the effect of dietary selenium on the primary and secondary immune response in calves challenged with infectious bovine rhinotracheitis virus found that whole blood and plasma GSH-Px activity increased in selenium supplemented group (0.2 mg/kg diet) but not in selenium deficient calves. Gill and Walker (2008) reported that mice fed with high selenium diet (121 µg/100g feed) for 49 days showed proliferation of spleen lymphocytes compared to that fed selenium sufficient control (18 μg/100g feed) indicating improved immune response of selenium fed animals. Vinu et al., (2012) observed lower incidence of disease in crossbred calves when supplemented with selenium yeast at the rate of 0.3 ppm.

Spears et al. (1986) found that selenium- vitamin E injections reduced calf death losses. Oxidative stress is associated with the production of free radicals and the inability of body to counteract or detoxify these harmful substances. Antioxidant activity of selenium prevents the production of free radicals due to peroxidation reactions. Reffett et al. (1986) concluded that selenium or zinc supplementation may individually improve an animal’s response to stress. Selenium improves neutrophil activity. Arthur et al.(2003) reported significantly higher candidacidal activity of neutrophils when selenium deficient mice were given intra peritoneal injection of sodium selenite at > 10 µg per kilogram body weight in 0.9 per cent sodium chloride solution.

But certain studies showed non-significant effect of selenium supplementation on immunity. Weiss et al.(1983) studied the role of selenium/vitamin E in disease prevention and weight gain of neonatal calves by injecting 0.078 mg selenium and 5.4 IU vitamin E/kg body weight and reported no reduction in the incidence of respiratory diseases. Effect of vitamin E (500 mg) and selenium (200µg) supplementation on immunity was studied in newborn jersey and buffalo calves from birth to 30 days by Afzal et al. (1988) could not found any significance in total leucocyte count, differential leucocyte count, antibody titre and susceptibility to disease on supplementing vitamin E (500mg) and selenium (200µg) to new born jersey and buffalo calves. Hoshino et al. (1989) from their studies on serum tocopherol, selenium levels and blood GSH-Px activities in calves with white muscle disease observed that white muscle disease in calves was attributable to nutritional muscular dystrophy caused by deficiencies in tocopherol and selenium in feed stuffs supplied to their dams.

Conclusion

Selenium was first given importance because of its toxicity, later it was identified that selenium is essential for animals for various life activities and also for developing proper immune mechanism against the invaders. There is only a narrow gap between toxic dose and dietary essential dose in case of selenium. Deficiency of selenium leads to white muscle disease in calves and toxicity leads to alkali disease. So it is better to follow FDA guidelines during supplementation of selenium (0.3 ppm) in the diet. As of now research works had proved the efficiency of organic form of selenium over inorganic selenium. Proper supplementation of selenium keeps the animal in good growth and health condition.

Conflicts of Interests

The author have not declared any conflict of interests

Reference

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