Selenium for ruminants: comparing organic and inorganic selenium for cattle and sheep
Published: July 20, 2007
By: R. L. KINCAID, M. ROCK, and F. AWADEH (Courtesy of Alltech Inc.)
Nutritional deficiencies of selenium (Se) in ruminants result in whitemuscle disease (Muth et al., 1958), loss of glutathione peroxidase activity and selenoproteinW (Yeh et al., 1997), and suppression of immunity (Yamini and Mullaney, 1985). Newborn ruminants are dependent upon the dam for selenium transfer via the placenta or mammary gland.
Because feeds grown in many areas of the world are deficient in selenium for livestock, selenium supplementation is often necessary. Methods that have been used for selenium supplementation include injection, drenching, administering selenium-laden boluses and trace mineral salt mixes. Inorganic selenium salts, primarily sodium selenite, are generally used in selenium supplements.
Organic selenium sources, such as plants and selenium yeast (Sel- Plex) contain selenoamino acids that are beneficial as selenium supplements.
Differences exist in the utilization of dietary selenium from the various chemical forms. Selenium in sodium selenite can be chemically reduced to insoluble forms by rumen microorganisms, thus lowering selenium absorption. Selenoamino acids can be nonspecifically incorporated directly into body protein (Kincaid, 1995) and presumably serve a selenium storage capacity.
Glutathione peroxidase (GSH-Px) was the first selenoprotein identified (Rotruck et al., 1973), but several additional selenoproteins since have been isolated. Among these selenoproteins are Types I, II, and III deiodinases responsible for peripheral deiodination of thyroxine (T3) to 3,5,3 tri-iodothyronine (T3) and other metabolites. Rats that are selenium deficient have significantly lower concentrations of T3 (Beckett et al., 1987; Behne et al., 1992; and Beckett et al., 1992).
Studies by Arthur et al. (1988) andWichtel et al. (1996) found that selenium-deficient dairy heifers also have lower concentrations of T3 and elevated T3, resulting in a lower ratio of T3 to T3. Tri-iodothyronine is the metabolically active thyroid hormone and is involved in growth, thermogenesis, and nutrient metabolism. Thus, lowered concentrations of T3 caused by selenium deficiency may contribute to health problems in ruminants.
Selenium is also involved in the immune function of animals. Larsen (1988) observed a trend for increased IgG concentrations in seleniumsupplemented ewes and lambs. Calves failing to absorb enough IgG have higher risk of morbidity (McGuire et al., 1976). In addition, Larsen (1988) reported significantly increased titers to tetanus toxoid in selenium supplemented lambs. Similarly, Turner and Finch (1990) reported a decreased lymphocyte response in lambs deficient in vitamin E and selenium.
Thus, there are biological measures beside GSH-Px activity that should be considered when evaluating selenium status of ruminants. Accordingly, two experiments were conducted to determine the effects of level and chemical form of dietary selenium on concentrations of thyroid hormones, selenium in tissues, and immunoglobulin status in dams and newborns.
Selenium supplementation of beef cows
PROCEDURES
Sixty mature beef cows were assigned to one of four dietary treatments consisting of free-choice access to salt mixes containing 20, 60, or 120 ppm Se as sodium selenite. The fourth treatment was 60 ppm Se as organic selenium from yeast (Sel-Plex).
Cows were fed their experimental diets from 90 days prepartum and were maintained on their respective treatments for two calving and breeding seasons. The cows were separated by treatment and rotationally grazed grass pastures during the summers and in winter were fed haylage, a concentrate, and ryegrass seed screening pellets in the first year and cereal graining screenings in the second year. Intakes of the salt mixes were recorded for each group (Awadeh et al., 1998b).
RESULTS AND DISCUSSION
The concentration of selenium in blood of cows at parturition differed significantly (P £0.01) among treatment groups with cows fed the 20ppm Se salt mixture having lower concentration of selenium (Table 1).
Concentrations of selenium in colostrum in year 1 were similar for all cows, but in year 2, concentrations of selenium in colostrum were higher (P £ 0.01 for cows given salt with 60 ppm Se as Sel-Plex than for control cows. Hemken et al. (1998) reported milk selenium tended (P£ 0.06) to be increased more by selenium in Sel-Plex than selenite.
Selenium concentrations in blood of newborn calves were increased by additional selenium in salt for the pregnant cows and were highest for calves of cows fed Sel-Plex in year 1 and higher than 20 and 60 ppm Se as selenite in year 2 (Table 2). In year 1, activity of GSH-Px in blood was increased by additional selenium supplementation of cows. The concentrations of selenium in liver of newborn calves were not affected by treatments.
Table 1. Effect of level and form of supplemental selenium in salt mixes fed free-choice to pregnant cows on selenium and thyroid hormones in blood and colostrum samples taken immediately postpartum.1
1Adapted from Awadeh et al., 1998b.
abcMeans followed by different superscripts differ, P<0.05.
Table 2. Effect of maternal intakes of selenium on selenium status and thyroid hormones in day-old calves1.
1Adapted from Awadeh et al., 1998b.
EU = nmol NADPH oxidized/min/mg hemoglobin.
abMeans followed by different superscripts differ, P<0.05.
Treatments affected (P £ 0.01) the concentration of T3, but not of T3, in serum of cows (Table 1). In addition, the ratio of T3:T3 was increased in cows given added selenium. Calves born to cows supplemented with 60 ppm Se as Sel-Plex had higher T3 concentrations at birth than calves from cows supplemented with 20 and 60 ppm Se as selenite (Table 2).
The ratio of T3:T3 in calves of cows supplemented with 120 ppm Se in the salt mix was higher than that in calves of cows fed salt with 20 and 60 ppm Se. The concentrations of T3 in calves is important because T3 enhances the synthesis of uncoupling protein, necessary for brown adipose tissue thermogenesis (Carstens, 1994).
Concentrations of IgG and IgM in serum of cows and their calves were significantly lower when given salt with 20 ppm Se (Table 3). Serum IgM concentrations were higher (P£ 0.05) in cows given salt with 60 ppm Se as Sel-Plex compared to cows supplemented with 60 ppm Se as selenite.
In the present study, salts with 60 or 120 ppm Se enhanced transfer of IgG from cow serum to colostrum but did not affect synthesis of IgM in the mammary gland. Swecker et al. (1995) found that cows supplemented with selenium had increased colostral IgG and their calves had increased IgG, but there was no effect of dietary selenium on IgM.
Table 3. Effect of maternal intakes of selenium on immunoglobulin concentrations in serum and colostrum of cows and serum of day-old calves.1
1Adapted from Awadeh et al., 1998b.
abcMeans followed by different superscripts differ, P<0.05.
Selenium supplementation of pregnant ewes
PROCEDURES
Pregnant ewes (n = 21) of mixed Ramboulliet and Polypay breeding, 5-6 years old, with an average body weight of 62.7 kg were randomly assigned to treatment. Ultrasound tests were conducted previously (about 60 days gestation) and only ewes suspected of being twin-bearing were used for the study.
Ewes were housed in pens of 7 according to treatment groups and fed a mid-gestation diet containing less than 0.02 ppm Se. Treatments were applied via trace mineralized salt mixes and consisted of: 1) control, no supplemental Se; 2) inorganic, 90 ppm Se as Na2SeO3; and 3) organic, 90 ppm Se as Sel-Plex.
Because of a treatment difference in the consumption of the trace mineral salts with added selenium during the first month of the trial, 50% ground corn was added to the trace mineral salt and the ewes were limit-fed the salts to allow for selenium intakes equivalent to about 0.3 mg Se/kg of diet dry matter for ewes supplemented with selenium.
At lambing, rectal temperature and body weight of each newborn lamb were recorded and a colostrum sample was collected from the ewe. One twin lamb was removed before suckling the ewe for eventual tissue collection.
The lamb was fed pooled bovine colostrum (25 ml colostrum/kg of body weight) initially and again 6 hrs later. At 12 hrs, blood samples were taken and lambs were euthanized with sodium pentobarbitol. Liver, kidney, heart, gastrointestinal tract and brown adipose tissue from the perirenal and pericardial regions were removed, weighed and frozen.
RESULTS AND DISCUSSION
Intake of selenium was increased by selenium supplementation and was similar between the two supplemented groups. Feed intakes and body weights were similar among treatment groups.
Concentrations of selenium in serum were depressed (P £ 0.05) in ewes receiving no selenium supplementation (Table 4). Overall, there was a linear decrease in concentrations of selenium in serum for ewes with length of gestation. The chemical form of the selenium supplement did not significantly affect the concentration of selenium in serum.
Van Ryssen et al. (1989) reported that while selenium from organic sources increased concentrations of selenium in whole blood of sheep, chemical form of selenium did not significantly affect plasma selenium. This also was reported in cattle by Awadeh et al. (1998a).
Accordingly, the concentrations of selenium in whole blood were increased (P £ 0.0001) by selenium supplementation with ewes supplemented with Sel-Plex tending to have the highest concentrations of selenium in blood at lambing. The difference in response between serum and whole blood to the selenium supplements indicated greater uptake by the red blood cell of selenium from Sel-Plex than selenite.
As expected, GSH-Px activities were greater in ewes given selenium supplements.
Body temperatures and birth weights were not affected by maternal treatments. Concentrations of selenium in whole blood of newborn lambs were increased (P£ 0.0001) 2-fold and 4-fold by the selenite and Sel-Plex supplements, respectively (Table 5).
The data are consistent with results of Schamberger (1986), providing further evidence that organic forms of selenium are more readily transported across the placenta. Concentrations of selenium in the liver of lambs were also significantly increased by selenium supplementation.
Although the difference between the selenite and Sel-Plex treatments in concentrations of selenium in liver was not statistically different, the trend is consistent with selenium from organic sources being more readily incorporated into protein than inorganic selenium (Kincaid, 1995).
Table 4. Effect of level and source of dietary selenium on concentrations of selenium, thyroid hormones, glutathione peroxidase activity, and immunoglobulins in ewes at lambing.1
1Blood samples were taken within 12 hr of parturition, approximately day 100 of the trial. EU = (moles of NADPH oxidized/min/ml of whole blood.
*P<0.05 **P<0.001 ***P<0.0001.
Table 5. Effect of maternal intake of selenium on concentrations of selenium, thyroid hormones, immunoglobulins and activity of glutathione peroxidase in newborn lambs.
EU = (moles of NADPH oxidized/min/ml of whole blood.
NS = nonsignificant, P £0.1; *P£ 0.1; **P £ 0.005; ***P£ 0.001; ****P £ 0.0001.
Concentrations of selenium in whole blood of lambs were positively correlated to the selenium concentrations in liver (r = 0.77). Activities of GSH-Px in blood of lambs were greatly increased (P £ 0.0001) when the dams were supplemented with selenium during gestation. In addition, ewes given the Sel-Plex had lambs with significantly higher GSH-Px activity than the lambs of ewes given selenite. The GSH-Px activity was highly correlated (r = 0.88) to selenium concentrations in whole blood of lambs.
Interactions of selenium and thyroid hormones
The concentrations of T3 in serum of control ewes were 39% lower in ewes supplemented with selenium (Table 4). Interestingly, the concentrations of T3 in the control ewes were also lower, thereby resulting in no change in the ratio of T3 to T3. Supplementation of ewes with selenium tended to increase T3 concentrations in the newborn lambs.However, there was no effect due to the chemical form of the added selenium (Table 5).
Selenium and measures of immunity
Lambs of control ewes had lower IgG concentrations in serum than lambs of ewes supplemented with selenium (Table 5).
Because all lambs were fed equivalent amounts of pooled bovine colostrum, the difference in IgG in the lambs was due to an effect of selenium on the lamb’s ability to absorb the IgG from the small intestine. Maternal IgG levels in serum and colostrum were not affected by selenium intake (Table 4). However, IgM was significantly increased in serum of ewes given added selenium.
These data indicate that selenium intake during pregnancy can affect maternal synthesis of IgM and the absorption of IgG by the newborn.
Summary
Some differences in results of these two trials are due to the greater selenium depletion in the ewes compared to the cows, and perhaps due to species differences.
In both trials, supplementation of pregnant cows and ewes with selenium generally improved the selenium status and increased concentrations of T3 and immunoglobulins in both the dams and their newborns. Thus, maternal selenium supplementation improved some of the measures predictive of susceptibility of newborn ruminants to disease.
The data further showed that selenium in Sel-Plex was transferred more readily to ovine fetus and colostrum than selenium in sodium selenite.
Thus, supplements containing Sel-Plexmay be particularly beneficial when total intakes of selenium are limited.
Because feeds grown in many areas of the world are deficient in selenium for livestock, selenium supplementation is often necessary. Methods that have been used for selenium supplementation include injection, drenching, administering selenium-laden boluses and trace mineral salt mixes. Inorganic selenium salts, primarily sodium selenite, are generally used in selenium supplements.
Organic selenium sources, such as plants and selenium yeast (Sel- Plex) contain selenoamino acids that are beneficial as selenium supplements.
Differences exist in the utilization of dietary selenium from the various chemical forms. Selenium in sodium selenite can be chemically reduced to insoluble forms by rumen microorganisms, thus lowering selenium absorption. Selenoamino acids can be nonspecifically incorporated directly into body protein (Kincaid, 1995) and presumably serve a selenium storage capacity.
Glutathione peroxidase (GSH-Px) was the first selenoprotein identified (Rotruck et al., 1973), but several additional selenoproteins since have been isolated. Among these selenoproteins are Types I, II, and III deiodinases responsible for peripheral deiodination of thyroxine (T3) to 3,5,3 tri-iodothyronine (T3) and other metabolites. Rats that are selenium deficient have significantly lower concentrations of T3 (Beckett et al., 1987; Behne et al., 1992; and Beckett et al., 1992).
Studies by Arthur et al. (1988) andWichtel et al. (1996) found that selenium-deficient dairy heifers also have lower concentrations of T3 and elevated T3, resulting in a lower ratio of T3 to T3. Tri-iodothyronine is the metabolically active thyroid hormone and is involved in growth, thermogenesis, and nutrient metabolism. Thus, lowered concentrations of T3 caused by selenium deficiency may contribute to health problems in ruminants.
Selenium is also involved in the immune function of animals. Larsen (1988) observed a trend for increased IgG concentrations in seleniumsupplemented ewes and lambs. Calves failing to absorb enough IgG have higher risk of morbidity (McGuire et al., 1976). In addition, Larsen (1988) reported significantly increased titers to tetanus toxoid in selenium supplemented lambs. Similarly, Turner and Finch (1990) reported a decreased lymphocyte response in lambs deficient in vitamin E and selenium.
Thus, there are biological measures beside GSH-Px activity that should be considered when evaluating selenium status of ruminants. Accordingly, two experiments were conducted to determine the effects of level and chemical form of dietary selenium on concentrations of thyroid hormones, selenium in tissues, and immunoglobulin status in dams and newborns.
Selenium supplementation of beef cows
PROCEDURES
Sixty mature beef cows were assigned to one of four dietary treatments consisting of free-choice access to salt mixes containing 20, 60, or 120 ppm Se as sodium selenite. The fourth treatment was 60 ppm Se as organic selenium from yeast (Sel-Plex).
Cows were fed their experimental diets from 90 days prepartum and were maintained on their respective treatments for two calving and breeding seasons. The cows were separated by treatment and rotationally grazed grass pastures during the summers and in winter were fed haylage, a concentrate, and ryegrass seed screening pellets in the first year and cereal graining screenings in the second year. Intakes of the salt mixes were recorded for each group (Awadeh et al., 1998b).
RESULTS AND DISCUSSION
The concentration of selenium in blood of cows at parturition differed significantly (P £0.01) among treatment groups with cows fed the 20ppm Se salt mixture having lower concentration of selenium (Table 1).
Concentrations of selenium in colostrum in year 1 were similar for all cows, but in year 2, concentrations of selenium in colostrum were higher (P £ 0.01 for cows given salt with 60 ppm Se as Sel-Plex than for control cows. Hemken et al. (1998) reported milk selenium tended (P£ 0.06) to be increased more by selenium in Sel-Plex than selenite.
Selenium concentrations in blood of newborn calves were increased by additional selenium in salt for the pregnant cows and were highest for calves of cows fed Sel-Plex in year 1 and higher than 20 and 60 ppm Se as selenite in year 2 (Table 2). In year 1, activity of GSH-Px in blood was increased by additional selenium supplementation of cows. The concentrations of selenium in liver of newborn calves were not affected by treatments.
Table 1. Effect of level and form of supplemental selenium in salt mixes fed free-choice to pregnant cows on selenium and thyroid hormones in blood and colostrum samples taken immediately postpartum.1
1Adapted from Awadeh et al., 1998b.
abcMeans followed by different superscripts differ, P<0.05.
Table 2. Effect of maternal intakes of selenium on selenium status and thyroid hormones in day-old calves1.
1Adapted from Awadeh et al., 1998b.
EU = nmol NADPH oxidized/min/mg hemoglobin.
abMeans followed by different superscripts differ, P<0.05.
Treatments affected (P £ 0.01) the concentration of T3, but not of T3, in serum of cows (Table 1). In addition, the ratio of T3:T3 was increased in cows given added selenium. Calves born to cows supplemented with 60 ppm Se as Sel-Plex had higher T3 concentrations at birth than calves from cows supplemented with 20 and 60 ppm Se as selenite (Table 2).
The ratio of T3:T3 in calves of cows supplemented with 120 ppm Se in the salt mix was higher than that in calves of cows fed salt with 20 and 60 ppm Se. The concentrations of T3 in calves is important because T3 enhances the synthesis of uncoupling protein, necessary for brown adipose tissue thermogenesis (Carstens, 1994).
Concentrations of IgG and IgM in serum of cows and their calves were significantly lower when given salt with 20 ppm Se (Table 3). Serum IgM concentrations were higher (P£ 0.05) in cows given salt with 60 ppm Se as Sel-Plex compared to cows supplemented with 60 ppm Se as selenite.
In the present study, salts with 60 or 120 ppm Se enhanced transfer of IgG from cow serum to colostrum but did not affect synthesis of IgM in the mammary gland. Swecker et al. (1995) found that cows supplemented with selenium had increased colostral IgG and their calves had increased IgG, but there was no effect of dietary selenium on IgM.
Table 3. Effect of maternal intakes of selenium on immunoglobulin concentrations in serum and colostrum of cows and serum of day-old calves.1
1Adapted from Awadeh et al., 1998b.
abcMeans followed by different superscripts differ, P<0.05.
Selenium supplementation of pregnant ewes
PROCEDURES
Pregnant ewes (n = 21) of mixed Ramboulliet and Polypay breeding, 5-6 years old, with an average body weight of 62.7 kg were randomly assigned to treatment. Ultrasound tests were conducted previously (about 60 days gestation) and only ewes suspected of being twin-bearing were used for the study.
Ewes were housed in pens of 7 according to treatment groups and fed a mid-gestation diet containing less than 0.02 ppm Se. Treatments were applied via trace mineralized salt mixes and consisted of: 1) control, no supplemental Se; 2) inorganic, 90 ppm Se as Na2SeO3; and 3) organic, 90 ppm Se as Sel-Plex.
Because of a treatment difference in the consumption of the trace mineral salts with added selenium during the first month of the trial, 50% ground corn was added to the trace mineral salt and the ewes were limit-fed the salts to allow for selenium intakes equivalent to about 0.3 mg Se/kg of diet dry matter for ewes supplemented with selenium.
At lambing, rectal temperature and body weight of each newborn lamb were recorded and a colostrum sample was collected from the ewe. One twin lamb was removed before suckling the ewe for eventual tissue collection.
The lamb was fed pooled bovine colostrum (25 ml colostrum/kg of body weight) initially and again 6 hrs later. At 12 hrs, blood samples were taken and lambs were euthanized with sodium pentobarbitol. Liver, kidney, heart, gastrointestinal tract and brown adipose tissue from the perirenal and pericardial regions were removed, weighed and frozen.
RESULTS AND DISCUSSION
Intake of selenium was increased by selenium supplementation and was similar between the two supplemented groups. Feed intakes and body weights were similar among treatment groups.
Concentrations of selenium in serum were depressed (P £ 0.05) in ewes receiving no selenium supplementation (Table 4). Overall, there was a linear decrease in concentrations of selenium in serum for ewes with length of gestation. The chemical form of the selenium supplement did not significantly affect the concentration of selenium in serum.
Van Ryssen et al. (1989) reported that while selenium from organic sources increased concentrations of selenium in whole blood of sheep, chemical form of selenium did not significantly affect plasma selenium. This also was reported in cattle by Awadeh et al. (1998a).
Accordingly, the concentrations of selenium in whole blood were increased (P £ 0.0001) by selenium supplementation with ewes supplemented with Sel-Plex tending to have the highest concentrations of selenium in blood at lambing. The difference in response between serum and whole blood to the selenium supplements indicated greater uptake by the red blood cell of selenium from Sel-Plex than selenite.
As expected, GSH-Px activities were greater in ewes given selenium supplements.
Body temperatures and birth weights were not affected by maternal treatments. Concentrations of selenium in whole blood of newborn lambs were increased (P£ 0.0001) 2-fold and 4-fold by the selenite and Sel-Plex supplements, respectively (Table 5).
The data are consistent with results of Schamberger (1986), providing further evidence that organic forms of selenium are more readily transported across the placenta. Concentrations of selenium in the liver of lambs were also significantly increased by selenium supplementation.
Although the difference between the selenite and Sel-Plex treatments in concentrations of selenium in liver was not statistically different, the trend is consistent with selenium from organic sources being more readily incorporated into protein than inorganic selenium (Kincaid, 1995).
Table 4. Effect of level and source of dietary selenium on concentrations of selenium, thyroid hormones, glutathione peroxidase activity, and immunoglobulins in ewes at lambing.1
1Blood samples were taken within 12 hr of parturition, approximately day 100 of the trial. EU = (moles of NADPH oxidized/min/ml of whole blood.
*P<0.05 **P<0.001 ***P<0.0001.
Table 5. Effect of maternal intake of selenium on concentrations of selenium, thyroid hormones, immunoglobulins and activity of glutathione peroxidase in newborn lambs.
EU = (moles of NADPH oxidized/min/ml of whole blood.
NS = nonsignificant, P £0.1; *P£ 0.1; **P £ 0.005; ***P£ 0.001; ****P £ 0.0001.
Concentrations of selenium in whole blood of lambs were positively correlated to the selenium concentrations in liver (r = 0.77). Activities of GSH-Px in blood of lambs were greatly increased (P £ 0.0001) when the dams were supplemented with selenium during gestation. In addition, ewes given the Sel-Plex had lambs with significantly higher GSH-Px activity than the lambs of ewes given selenite. The GSH-Px activity was highly correlated (r = 0.88) to selenium concentrations in whole blood of lambs.
Interactions of selenium and thyroid hormones
The concentrations of T3 in serum of control ewes were 39% lower in ewes supplemented with selenium (Table 4). Interestingly, the concentrations of T3 in the control ewes were also lower, thereby resulting in no change in the ratio of T3 to T3. Supplementation of ewes with selenium tended to increase T3 concentrations in the newborn lambs.However, there was no effect due to the chemical form of the added selenium (Table 5).
Selenium and measures of immunity
Lambs of control ewes had lower IgG concentrations in serum than lambs of ewes supplemented with selenium (Table 5).
Because all lambs were fed equivalent amounts of pooled bovine colostrum, the difference in IgG in the lambs was due to an effect of selenium on the lamb’s ability to absorb the IgG from the small intestine. Maternal IgG levels in serum and colostrum were not affected by selenium intake (Table 4). However, IgM was significantly increased in serum of ewes given added selenium.
These data indicate that selenium intake during pregnancy can affect maternal synthesis of IgM and the absorption of IgG by the newborn.
Summary
Some differences in results of these two trials are due to the greater selenium depletion in the ewes compared to the cows, and perhaps due to species differences.
In both trials, supplementation of pregnant cows and ewes with selenium generally improved the selenium status and increased concentrations of T3 and immunoglobulins in both the dams and their newborns. Thus, maternal selenium supplementation improved some of the measures predictive of susceptibility of newborn ruminants to disease.
The data further showed that selenium in Sel-Plex was transferred more readily to ovine fetus and colostrum than selenium in sodium selenite.
Thus, supplements containing Sel-Plexmay be particularly beneficial when total intakes of selenium are limited.
| Conclusions The finding that low, but not deficient, intakes of selenium by pregnant cows and ewes affect Ig and T3 levels has large significance for health and survival of newborns. Passive immunity and heat production from brown adipose are required for newborn survival; and both events may be influenced by maternal selenium intakes. |
References
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Authors: R. L. KINCAID1, M. ROCK1, and F. AWADEH2
1 Department of Animal Sciences, Washington State University, Pullman, Washington, USA
2 NCARTT, Ammon, Jordan.
1 Department of Animal Sciences, Washington State University, Pullman, Washington, USA
2 NCARTT, Ammon, Jordan.
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