Selenium supplementation strategies for livestock in Oregon

Selenium (Se) is an essential trace mineral for livestock. Selenium deficiencies have been described in many species, including cattle, sheep, goats, horses, swine, white-tailed deer and elk.

Clinical Se deficiency can cause nutritional myodegeneration , or white muscle disease. The correlation between white muscle disease and selenium deficiency was first discovered in 1958 by O.H. Muth and others at Oregon State University. The disease is characterized by muscle weakness, heart failure, unthriftiness — failure to grow or put on weight — and death. Se deficiency also causes effects that are not immediately observable and result in poor livestock performance (see Table 1).

Figure 1. Young animals are particularly vulnerable to selenium deficiency.

Credit: Lynn Ketchum, © Oregon State University.

Selenium is the only micronutrient regulated as a livestock feed additive by the Food and Drug Administration because of its potential toxic effects. The FDA first approved Se supplementation of feedstuffs in 1974 but only for use in swine, chicken and turkey diets. From 1974 to 1986, the FDA amended regulations for supplementing inorganic Se in feed, including recommendations for sheep, beef and dairy cattle, chickens and ducks. In 2003, FDA included organic Se yeast as a feed additive for livestock.

The Oregon Department of Agriculture requires labeling of Se-supplemented feedstuffs because of potential toxicity when mishandled. Selenium, although essential for animals, can be toxic when animals consume certain Se formulations in excess. Thus, it is important that livestock producers understand Se supplementation strategies to protect the health of their herd.

The purpose of this publication is to provide information and discussions on:

The role of Se in the livestock diet.
Supplementation rates for livestock.
Forms of Se.
Methods of supplementation.
Economic analysis of different types of Se supplementation.
Guidelines for Se supplementation in livestock.
Research and references useful to Oregon livestock producers.

Role of selenium in the livestock diet

Selenium in soil and related forage

Selenium deficiency in livestock is caused by low intake of bioavailable Se. Livestock forage — whether range, pasture or hay reflects the available Se content of the soil on which it is grown (see Figure 2). Selenium levels in soil vary regionally. Detailed information on Se in the soil can be found in the National Geochemical Survey database.

Selenium exists in soil in various forms, including selenides, elemental Se, selenites, selenates and organic Se compounds. Soil pH influences the bioavailability of Se for plants, meaning the degree to which plants can take up Se. Acidic soil (lower pH) decreases plant uptake of Se, whereas alkaline conditions (higher pH) increase Se uptake. In addition, different plant species may incorporate soil Se at varying rates. For example, alfalfa has been shown to take up Se much better than red clover in Se-poor soils.

Selenium’s role in livestock health

In animals, Se is found in greatest concentrations in kidney and liver tissues but also is stored in muscle. Selenium works closely with antioxidants, such as vitamin E. Disorders caused by Se deficiency often are characterized by low concentrations of both Se and vitamin E.

Research has shown that the skeletal and cardiac muscles of very young livestock (3 to 8 weeks of age) are more often affected by low Se intake than those of older livestock. Signs of Se deficiency include muscle stiffness and tremors, motor disturbances, hind-end paralysis and heart failure.

Figure 2. Regional distribution of forages and grain containing low, variable or adequate levels of selenium in the United States

Reprinted with permission from Selenium in Nutrition, 1983 by the National Academy of Sciences, courtesy of the National Academy Press, Washington, D.C.

OSU studies highlighting beef Se research

OSU researchers fed Se-fortified alfalfa hay to weaned beef calves and compared their growth rate to control animals. Calves fed Se-fortified alfalfa hay had higher blood Se concentrations that corresponded to the amount of Se applied to the fields. The calves fed Se-fortified alfalfa hay also weighed up to 10% more than calves fed alfalfa without Se fortification. Calves on the Se-enriched forage also showed increased antibody titers to a common cattle vaccine, which resulted in an improved vaccination response. Subsequently, in the feedlot, calves previously fed the highest Se concentration in fortified hay had lower death rates and greater slaughter weights compared with other groups in the trial. See References 1 and 2.

Selenium deficiency also can manifest in older animals as a subclinical disease (a disease or condition that has no obvious signs).

**Table 1. Effects of Se deficiency or suboptimal Se concentrations, and benefits of Se supplementation in livestock.**
Livestock	Selenium deficiency	Benefits of supplementation
Cattle
	• Poor calf health	• Control of mastitis in dairy herds
	• Decreased immune function	• Control of retained placenta
	• Failure to thrive	• Improved calf weight gain
	• Uterine infection	• Improved immune system
	• Mastitis	• Improved fertility
	• Retained placenta
	• Reduced fertility in cows and bulls
Sheep
	• Unthriftiness (failure to grow or put on weight)	• Increased fertility
	• Growth depression	• Increased lamb weight gain
	• Decreased twinning	• Increased lamb vigor
	• lmmunosuppression	• Increased reproductive performance in hot weather
	• Increased susceptibility to bacterial and viral infections	• Increased antibody response
	• Foot rot	• Increased ewe colostral antibodies
		• Improved innate immunity to footrot
Goats
	• Likely similar to cattle and sheep	• Reduced level of mastitis in dairy goats
Horses
	• Delayed or reduced immune response to vaccination	• Improved immune function
	• Decreased immune function	• Improved fertility
	• Myopathy, difficulties in locomotion, suckling, swallowing, respiration and cardiac function

White muscle disease is the most well-known disease caused by absolute Se deficiency. In necropsied animals, greyish-white streaking is evident in skeletal muscle myodegeneration and myocardial lesions. In cattle, sheep and goats, Se deficiency also can cause abortion, stillbirth or death shortly after birth. Table 1 summarizes some of the effects of Se deficiency and the benefits of Se supplementation in livestock diets.

Find additional information on the in-depth biological functions of Se in “References” listed at the end of this publication or or in a review on trace mineral metabolism by Swecker and Van Saun.

Liver biopsy samples are useful in assessing Se status but not necessarily better than whole-blood samples. Tissue Se concentrations can be measured in small liver biopsy samples obtained using a Tru-Cut-type biopsy instrument. However, tissue biopsies may be expensive and time- consuming for livestock producers.

A whole-blood analysis is a quicker and simpler form of testing Se status in an animal. Whole-blood Se is considered a more desirable measure of long-term Se status (Se storage) than serum or plasma Se concentrations, which are sensitive to short-term changes in diet. In cattle fed free- choice minerals, intake can vary greatly from day to day; this can cause plasma or serum Se concentrations to inaccurately reflect Se status.

Hemolysis of red blood cells during processing will also falsely increase serum Se concentrations, because 60% to 70% of the total Se in blood is present in erythrocytes. Because of the slow turnover of erythrocytes, whole-blood Se gives a better overall measure of long-term Se status. Most of Se in erythrocytes is present in hemoglobin and the enzyme, glutathione peroxidase (GSHpx). Whole blood Se positively correlates (r = 0.85) with whole blood GSHpx activity.

Liver Se concentrations also reflect Se status. However, concentrations of liver Se that suggest deficiency in adult cattle and sheep vary greatly in the literature. Selenium liver concentrations are greater in fetuses and young calves than in adults. Fetal liver Se concentrations are at least twice as high as maternal levels but positively correlated with maternal liver Se.

Table 2 lists the normal range of whole-blood Se concentrations in livestock. In most regions of Oregon, except for some areas on the eastern side of the state, whole-blood Se concentrations are generally below the normal range.

**Table 2. Reference ranges for selenium concentrations in whole blood (WB) and liver biopsy (dry tissue basis) in livestock.**
Livestock	Age class	WB-Se concentration (ng/mL)	Liver biopsy Se concentration (µg/g)
Cattle	Calves (0-30 days) Older than 30 days	100-250 120-300	1.5-3.5 0.7-2.5
Sheep	Lambs to adults	120-350	0.8-3.0
Goats	Kids to adults	170-300
Horses	Foals (0-30 days) Older than 30 days	70-200 160-275

Source: Diagnostic Center for Population and Animal Health, Michigan State University

Selenium toxicity and livestock death can occur when animals receive excessive amounts of Se in their diet (for example, if sodium selenite is added to a concentrate or feed over tolerable levels). Death also can occur when excessive amounts of inorganic Se are injected. Consuming Se-accumulator plants, high in methyl-selenocysteine (Me-SeCys), can also poison animals. These plants, including Astragalus, Brassica and Stanleya species, survive in soils high in Se. Although livestock do not typically eat these plants, take care when pasturing animals in areas where they grow.

The ODA requires a label on all commercial feeds. Feeds that contain 0.5 ppm Se or more must guarantee the minimum and maximum Se levels listed on the label. This rule applies to both feed ingredients and mixed feed. It pertains to feeds produced in Oregon, Oregon-based labelers and feed imported into Oregon from other states or countries. The ODA does periodic testing of feeds to monitor Se content. For more information on the Oregon supplemental label and on testing of commercial feeds, go to the ODA website.

At OSU’s Soap Creek Ranch, mature beef cows that grazed Se-fertilized forage (13.5 g Se/acre mixed with nitrogen fertilizer) for six weeks had significantly higher whole blood-Se concentrations post-grazing compared with cows that received six weeks of sodium selenite supplementation (200 mg Se/kg salt) through a free choice salt-mineral mix, and compared with a third group of cows that had unlimited access to sodium selenite supplementation (120 mg Se/kg salt) in a salt-mineral mix. Whole blood-Se concentrations in Se-forage-fed cows remained higher for the next four to five months compared with Se-salt-supplemented cows. In this study, the short-term exposure of cattle to Se-fertilized forage increased whole blood-Se concentrations within several weeks. These cows maintained adequate Se blood concentrations, even without additional Se supplementation, throughout the grazing period. See Reference 3.

Supplementation rates for livestock

In 1987, the FDA increased Se supplementation rate from 0.1 to 0.3 mg Se/kg (ppm) in feed for cattle, sheep, swine, chickens, turkeys and ducks. For cattle, salt-based trace mineral supplements can contain up to 120 ppm Se. They must not exceed a daily supplemental maximum intake of 3 mg Se/head. For sheep, salt-based mineral supplements can have up to 90 ppm and Se intake must not exceed the maximum daily dose of 0.7 mg Se/head. In 2003, the organic form of Se in yeast was approved for addition to beef cattle diets at 0.3 mg Se/kg in feed. These amounts are for supplemental Se and do not consider natural Se concentrations already present in feed. That is why it is important to know the Se content of feeds.

The FDA does not regulate the rate of Se administered to horses; the rate for horses is set through industry standards. However, according to the National Research Council, 0.1 mg/kg (ppm) in feed is sufficient for the mature horse. This is equivalent to 1 mg for a 400 kg horse. Up to 3 mg per day has been shown to improve immune function in active equine.

Forms of selenium

Selenium supplements are commercially available in two broad chemical forms, inorganic and organic.

Inorganic Se

Sodium selenite and sodium selenate salts are the two inorganic sources of Se that are approved for use in livestock. The selenite form is used most commonly because of its commercial availability. The effects of inorganic Se are variable and often of short duration. Compared with organic, inorganic Se sources are less incorporated into rumen microorganisms for later digestion in the small intestine and instead are metabolized to Se forms that are not bioavailable.

During the last eight weeks before calving, dairy cows at the Columbia River Dairy in Boardman, Oregon, were supplemented with Se-yeast once weekly and received sodium selenite in their ration. Selenium-supplemented cows had 52% higher Se concentrations in whole blood at calving and at 14 days of lactation. In addition, Se-yeast supplementation improved antioxidant status and immune responses in cows after calving without negatively impacting other micronutrients and energy status. Calves born to Se-yeast-supplemented cows had higher whole blood-Se concentrations for the first two weeks, higher IgG absorption efficiency, higher serum-IgG concentrations and higher total serum-IgG content compared with calves born to Se-adequate control cows. Overall, feeding cows supranutritional Se-yeast supplement during the dry period improved whole blood-Se concentrations and IgG status of their calves. See References 4 and 5.

Beef cows were fed Se-enriched alfalfa hay (amendment rate was 45 or 90 g Se/ha as sodium selenate) during the third trimester of gestation to determine if passive transfer of antibodies in colostrum to their calves was enhanced. Data showed that feeding Se-biofortified alfalfa hay to beef cows during the last trimester of pregnancy resulted in increased whole blood-Se concentrations in cows and calves, increased colostral Se and IgG1 concentrations, but no effect on serum IgG1 concentrations in calves. Using ovalbumin as a surrogate marker for IgG absorption and a model for IgG1 passive transfer, results showed that if calves do not receive adequate colostrum within the first 12 hours of age to reach maximum pinocytosis, prior supranutritional Se supplementation of the mother improves absorption efficiency in their calves. See References 6 and 8.

Organic Se

When Se replaces sulfur in an amino acid, it is in the organic form. The Se in forages exists mainly as selenomethionine. Because of its organic form, this Se is less toxic than the inorganic form. When consumed by animals, it can be incorporated into body proteins, such as muscle tissue, in place of methionine. This unique property of selenomethionine results in Se being released with protein turnover — that is, during muscle growth. Thus, it is available to the animal for much longer than Se from traditional inorganic salt forms, such as sodium selenite.

Organic Se has been shown to have greater bioavailability for ruminants than inorganic sources. Research shows that ruminants grazing forages fortified with organic Se (agronomic biofortification), compared with ruminants having free choice access to selenite-containing mineral premixes, have higher whole-blood Se concentrations that persist for longer periods. Furthermore, supplementation with organic Se can have effects on whole-blood Se status many months beyond the end of the supplementation period. The increased bioavailability with organic Se sources leads to greater body reserves of Se. Supranutritional dosages of organic Se for a short time in the production cycle may also decrease or eliminate the need for year-round supplementation, as organic Se is stored as selenomethionine (SeMet) in proteins and released with normal protein turnover in the body.

The nasopharyngeal microbiota in cattle plays an important role in overall respiratory health, especially when stresses associated with weaning, transport and adaptation to a feedlot affect the normal respiratory defenses. Three studies were conducted to determine whether feeding weaned beef calves Se-enriched alfalfa hay for nine weeks in a preconditioning program prior to entering the feedlot altered nasal microbiota. In the first study, we concluded that feeding Se-biofortified alfalfa hay to weaned beef calves prior to entering the feedlot is a strategy for increasing nasopharyngeal microbial diversity. In the second trial, we showed that feeding Se-biofortifed alfalfa hay for nine weeks was effective at increasing whole blood-Se concentrations, increasing the body weight of weaned beef calves and increasing slaughter yield grades. Feeding Se-enriched alfalfa hay diversified the nasal microbiome and improved health and growth in the feedlot. It resulted in greater carcass weight and quality at slaughter. The third study was conducted to determine whether Se supplementation of dams during pregnancy improved health and performance of calves at weaning. We found that Se supplementation of pregnant cows is effective at increasing the whole blood-Se concentration of newborn calves, and the increase can be sustained until weaning for calves born to dams supplemented during the third trimester of pregnancy. However, the increase in WB-Se concentrations is small by weaning time. It does not result in beneficial changes in the nasal microbiome. Thus, calves should be fed Se-biofortified forages again at weaning in a preconditioning program to diversify the nasal microbiome before entering the feedlot, and consequently, to see benefits in carcass measurements at slaughter. See References 7, 9 and 11.

Methods of selenium supplementation

How much Se an animal absorbs and uses depends, in part, on the form of Se provided. Convenience and cost are two factors that determine the methods for administering Se. These methods include:

Injections
Salt-mineral mixes
Se yeast
Se-fortified feed
Se amended forage crops (currently only approved in Oregon and abroad)
Rumen boluses (currently only approved in California)

Injections

Injectable preparations containing Se can be given either subcutaneously (just below the skin) or intramuscularly (into the muscle) and must be obtained through approval from a veterinarian. When a labeled product gives you the option, choose sub-Q delivery for meat quality purposes. A Se injection can prevent white muscle disease in young livestock because it will quickly raise the blood levels of Se. Selenium injections are short-term fixes for both young and older livestock. Different concentrations of injectable, inorganic Se are available for different species and sizes of animals.

Be sure to follow label recommendations; overdose can be toxic. Some animals have died due to the wrong product or the wrong dosage being given.

Preparing an injection.

Credit: Pennstatenews/CC BY

Mineral supplement and premixes

Frequent intake of a Se-containing mineral mix provides continuous Se supplementation as long as the mineral supplement is available. Premixes are a concentrated source of Se and other minerals that require dilution with salt or other feeds in the ration. Be careful not to oversupply minerals by using these improperly. Salt-mineral mixes exposed to excessive rainfall may cause Se to leach out of the mix or convert to insoluble compounds, which can greatly reduce the intake of usable Se in the diet. When this occurs, it is possible that animals in a herd or flock will not consume a consistent amount of Se. Additionally, animals differ in their consumption of supplements. As a result of these factors, a wide range of whole-blood Se concentrations may exist in a group of animals consuming Se-fortified salt-mineral mixes.

Se-yeast

Se yeast can be mixed in diets, top-dressed onto feeds, placed in gelatin capsules and given as boluses or administered as a drench for individual animal consumption. For example, sheep and goats can be treated once a week rather than daily. Cows can be given gelatin capsules filled with Se-yeast, which are then administered orally with a balling gun weekly. Seven daily doses are compressed into one weekly dose for ease of administration. The organic Se-yeast can be purchased from a commercial source, typically with a guaranteed analysis of 2 g/kg of organically bound Se, with about 80% being SeMet. For sheep, the weekly dose can be mixed with water and administered orally as a drench.

Fortified feed supplements

You can also use commercial feeds supplemented with Se. However, it is important to know whether the Se in the feeds is inorganic or organic. Animals that consume organic Se retain more Se because it is better absorbed in the intestinal tract and there are fewer concerns about toxicity. Feeding Se-fortified feed can provide a more consistent intake of Se.

Fertilization

For over 25 years, research at OSU has demonstrated the potential for using Se as an amendment added to fertilizer to increase Se content in forage (pasture or hay) for livestock. This approach adds organic Se to an animal’s diet through agronomic biofortification. Agronomic biofortification increases concentrations of essential elements (such as Se) in the edible portions of crop plants. This practice can overcome the inconsistent intake of salt-mineral mixes and the short-term effects of injected Se. Because of its organic form, higher amounts of Se can be provided safely with Se fertilization. Not every pasture on the ranch needs to be amended with Se. One pasture in a grazing rotation can supply enough Se for the livestock.

Research in New Zealand, confirmed by OSU trials, found that sodium selenate is taken up more efficiently by plants than is sodium selenite. The recommended application level is 5 to 10 grams of actual Se per acre to achieve adequate levels of Se in forage. Sodium selenate is 42% Se. An application rate of 12 to 24 grams of sodium selenate per acre will provide the recommended 5 to 10 grams of actual Se per acre.

To determine the effects of Se-supplementation during different pregnancy stages on fetal programming, cows were given Se-yeast filled boluses (105 mg of Se/wk for 13 weeks; 5× the level recommended by NRC) during the first (TR1), second (TR2), or third (TR3) trimester of gestation. Blood and muscle tissue samples were collected from calves at birth. Whole-blood Se concentrations of newborn calves were progressively higher from CTR, TR1, TR2 to TR3. In contrast, muscle Se concentrations of newborn calves were only increased in the TR3 group. Selenium supplementation downregulated genes involved in adaptive immunity in calves from all Se treatment trimesters. Selenium supplementation in the last trimester of pregnancy resulted in the upregulation of myosin and actin filament-associated genes, potentially allowing for optimal muscle function and contraction. These findings suggest a beneficial effect of supranutritional maternal organic Se supplementation during late gestation on Se-status and muscle development and function of newborn calves. We also looked at the gene expression of monocyte blood cells collected from these cows at parturition. The main effects of supranutritional Se-supplementation on gene expression were downregulation of immune-related pathways and their regulatory elements, and limitation of both the immune response to microbial stimuli and collateral damage to adjacent healthy tissue. See References 10 and 14.

A pelleted material from New Zealand (called Selcote Ultra®) contains 25% sodium selenate (quick-release) and 75% barium selenate (slow-release), which is 4.5 grams of actual Se per pound. This product is approved for use in Oregon by the ODA. It can only be mixed with fertilizer by a licensed fertilizer dealer. Recommended application rates of Selcote Ultra are 1 to 2 pounds per acre. Late winter or early spring applications are most effective; however, there is some evidence that a fall application will provide sufficient Se for plant uptake in the spring. Hay produced from Se-fertilized forage is another excellent source of organic Se. You may obtain Selcote Ultra through your fertilizer dealer.

An animal technician administers a bolus to a cow.

Credit: Scott Bauer, USDA

Se used as a fertilizer can increase Se concentrations in forage for livestock.

Credit: Gene Pirelli, © Oregon State University

Selenium-fortified boluses

These small, Se-containing cylinders are only approved for use in cattle in California. The bolus stays in the rumen, where it gradually releases Se. A bolus can provide Se to animals in grazing areas where supplementation is not feasible.

Economic analysis of Se supplementation methods

Amending pasture with Se during fertilizer application is a cost-effective way to provide livestock with dietary Se (Table 3).

In a scenario where Selcote Ultra® is $10/lb (plus any blending fee) and the application rate is 1 lb/acre, a 5-acre pasture costs approximately $50 for a year’s worth of Se in that pasture. If the carrying capacity is 5 animal unit months (AUM) per acre, the 5-acre Se pasture has 25 AUM. With rotational grazing, about 10 cows (or 63 sheep) can graze there for two months (60 days or three 21-day rotations). The livestock will receive enough Se to meet their requirements throughout the grazing season even though Se has not been applied to the other pastures they graze. Se supplementation for 10 cows would cost $5 per cow for a 12-month supply.

Table 3. Cost comparison of different Se supplementation methods.*
Cost for 30-day supply of selenium supplementation ($/hd.)
Animal	Pasture	Injection	Block	Pre-mix
1,200-lb cow	$0.40	$3.00	$0.58	$0.66
150-lb ewe	$0.07	$1.50	$0.14	$0.15

*This analysis is based on 2024 prices. It does not account for other nutrients contained in the different products nor the effectiveness of different methods to maintain adequate blood Se levels in the animals. Review the information in the previous sections for the pros and cons of each method.

Guidelines for providing selenium supplementation

The following guidelines will help to:

Assess the current Se status of your herd or flock. Using pooled whole blood samples can reduce costs.
Calculate the daily consumption of Se and other minerals from base feed and supplements.
Develop a Se-supplementation program that takes into account the health of your animals and the economics of your farm or ranch.

An important first step in this process is to contact local resource people, such as university Extension faculty or a local veterinarian, to learn more about Se-supplementation methods and costs.

Do you live in an area where soil concentrations of Se are low?
Suggestion: Check the map in this publication (Figure 2), or check with your local Extension or National Resources Conservation Service office.
Do you know if Se levels on your range or pastures are adequate, low or high?
Suggestion: Consider sending a sample of your forage to a laboratory that measures Se by the ICP-MS method (for example, Michigan State University’s Diagnostic Center for Population and Animal Health or Utah State Diagnostic Lab).
Are you seeing any signs of Se deficiency in your animals?
Suggestion: Refer to Table 1 for signs of Se deficiency in livestock.
Consider testing blood from your entire herd or a representative subsample to look at Se concentrations.
Suggestion: Work with your veterinarian to determine a plan for obtaining and submitting samples. Analysis of blood samples is often the most practical way to determine if Se intake from forages and feeds is adequate.
Are you feeding Se-supplemented feed in addition to range/pasture grazing? If so, where is that feed from?
Suggestion: Check labels for Se concentration in feed. If that is not available, consider testing the feed.

By following these guidelines, you can take the necessary steps to accurately determine the Se status of your livestock herd. Once you have this information, you can develop a plan for Se supplementation that is tailored to your specific needs. Wise use of Se supplementation will benefit livestock producers and contribute to their livestock’s overall health.

We are currently summarizing research findings in beef cows to determine the best time during pregnancy to supplement with Se to optimize humoral immunity at parturition. All beef cows had access to a mineral supplement containing 120 mg/kg of Na selenite. In addition, cows received Se supplementation of 105 mg Se/week from Se-yeast boluses administered once weekly during their specific treatment trimester (TR1, TR2, or TR3) for 13 weeks. Blood was collected at parturition. Results showed that supranutritional Se-yeast supplementation increased whole blood-Se concentrations regardless of the trimester of supplementation. Some vaccine titers were higher in cows at parturition who received Se supplementation during later trimesters of pregnancy. Complement-mediated bacterial killing percentages were greater in TR2 and TR3 cows compared with TR1 and CTR cows. These findings suggest that Se supplementation during TR2 or TR3 may help combat infectious disease challenges during the periparturient period in beef cattle. See Reference 15.

OSU studies highlighting sheep Se research

Thirty ewes from the OSU Sheep Center were sorted randomly into two groups. One group of 15 ewes grazed Se-fertilized pasture (13.5 g Se/acre mixed with nitrogen fertilizer) for 40 days with no salt mineral supplement provided. Whole blood-Se levels were significantly higher for nine months for ewes grazing the Se-supplemented forage than for ewes receiving only the salt mineral supplement containing sodium selenite at 200 mg/kg. See Reference 17.

In another study, 240 ewes were divided into eight groups and drenched with inorganic and organic forms of Se, respectively. A control group received no Se supplement. Selenium concentrations in ewe blood and milk and in their lambs were greater in ewes drenched with organic Se yeast than ewes drenched with inorganic sodium selenite. In addition, concentrations of Se in lambs’ whole blood, blood serum and skeletal muscle increased in a dose-response manner based on the dose of Se received by ewes. Weekly oral drenching of ewes with organic Se yeast during gestation and lactation resulted in a more efficient transfer of Se from ewe to lamb than did weekly oral drenching with inorganic sodium selenite. See References 20, 21, 22 and 23.

In a study involving sheep affected by footrot, the affected animals were split into two groups. Once monthly, one group was injected with inorganic Se (sodium selenite) and the other with saline solution. The animals were checked for footrot lesions periodically over 15 months and rated on a scale of lesion severity. The footrot-affected sheep that received Se injections showed a decrease in footrot lesions over time compared with the group that did not receive Se injections. In addition, adaptive immune responses in Se-supplemented sheep were higher than in non-Se-supplemented sheep. See References 18 and 19. Subsequent studies showed that supranutritional Se yeast supplementation does not prevent footrot, but does alter whole blood neutrophil gene expression profiles associated with innate immunity, including reversing those impacted by footrot. Se supplementation restores innate and humoral immune response in footrot-affected sheep. See References 24 and 25.

Stress during transport may be linked to increased generation of reactive oxygen species, the removal of which requires glutathione and Se. Feeder lambs were studied to determine the effect of transport for eight hours followed by another 16 hours of feed deprivation. Body weight was transiently decreased. Results showed that transport and feed deprivation resulted in fatty acid and Se mobilization from tissue stores, with a coincident decrease in glutathione concentrations. See Reference 26.

To evaluate the effect of Se-yeast supplementation on gastrointestinal parasites, 30 ewes per treatment group were drenched weekly with Se yeast at 4.9 mg Se/week (maximum FDA-allowed concentration), or supranutritional concentrations (14.7 and 24.5 mg Se/week) starting in early fall for 85 weeks. During breeding season (fall), ewes were kept on pasture. Ewes receiving 24.5 mg Se/week had lower fecal trichostrongyle egg counts compared with ewes receiving no Se or ewes receiving 4.9 mg Se/week as Se yeast. In winter, fecal trichostrongyle egg counts decreased, and group differences were not apparent. During lambing season (spring), ewes were kept in the barn and fecal trichostrongyle egg counts increased again, although no group differences were observed. However, none of the ewes receiving supranutritional Se yeast, but four of the ewes receiving lower Se dosages, had H. contortus egg counts greater than or equal to 1,000 eggs/g feces. These results suggest that supranutritional Se-yeast supplementation may enhance resistance to naturally occurring H. contortus gastrointestinal parasitism in sheep. See Reference 27.

Despite being readily available, we have observed low Se status in cattle and sheep offered traditional inorganic Se supplements in mineral mixtures. A study was undertaken to determine whether rumen microbes alter the bioavailability of Se sources commonly used in mineral Se supplements. Rumen microorganisms were isolated from ewes and incubated in the lab with different forms of inorganic (Na selenite; Na selenate) and organic Se (selenomethionine, SeMet). Total Se incorporated into rumen microbes and the amount of elemental Se formed were measured. Incorporation of Se into microbial mass was 13-fold greater for SeMet than no-Se control. No differences were observed between inorganic Se sources (both threefold greater than no-Se control). Formation of nonbioavailable elemental Se was less for rumen microbes incubated with SeMet compared with inorganic Se sources. Thus, oral bioavailability of organic SeMet is greater compared with inorganic Se sources because of greater microbial incorporation of Se and decreased formation of elemental Se. See Reference 28.

OSU studies highlighting forage Se research

Research conducted in several counties around Oregon determined that sodium selenate (1.3 lb/acre) and sodium selenite (1.3, 2.4 and 4.8 lb/acre) applied to pastures in early spring increased forage Se concentrations throughout the grazing season. Sodium selenate provided the highest forage Se content in year 1. Plots with selenite treatments gave a dose-dependent increase in forage Se content compared with the control. Two years after Se application, plots that were previously treated with selenate or the highest rate of selenite, had forage Se concentrations higher than the control. Applications of Se had no effect on forage yield. These data suggest that selenite and selenate fertilization increase forage Se concentrations for up to two years. See Reference 36.

After finding that forage Se content could be increased using soil-applied Se (selenate and selenite), OSU researchers investigated the effects of Se amendments applied at the time of traditional nitrogen-phosphorus-potassium-sulfur (NPKS) fertilizer in a split-plot design experiment. Treatments were sodium selenate (0, 45 and 90 g Se ha-1) and springtime fertilizer (none, NPK for grasses/PK for alfalfa and NPKS/PKS fertilization at amounts adapted to meet local forage and soil requirements). Forage dry matter yield; N, S and Se (concentrations and yield); and agronomic efficiencies were determined. This two-year study was conducted on four representative forage fields: orchard grass in Terrebonne (Central Oregon), grass-clover mixture in Roseburg (Southwestern Oregon) and both grass mixture and alfalfa fields in Union (Eastern Oregon). Fertilization promoted forage growth and increased forage N concentrations. Selenate amendment linearly increased forage Se concentration without adversely affecting forage yields, N and S concentrations, or N and S agronomic efficiencies. Nearly all incorporated Se was contained in the first two cuts (87% and 9% in first and second cuts, respectively) as selenomethionine. Without Se amendment, forage Se concentrations were low and further decreased with fertilization (dilution effect). This confirms observations by farmers in Oregon that fertilizer containing sulfur decreases forage Se concentrations in non-Se amended fields. Importantly, S fertilization did not interfere with Se uptake in Se-amended plots. Among forages, alfalfa had greater Se concentrations under low soil Se conditions. In contrast, grass-dominated forages had higher Se concentrations after Se-amendment. In conclusion, the co-application of NPKS/PKS fertilizers and foliar sodium selenate in spring is an effective strategy to increase forage total Se concentrations, and highly bioavailable selenomethionine concentrations, while maintaining optimal growth and quality of Oregon forages. See References 33, 35 and 37.

Less was known about how forage Se species and Se concentrations were affected by high selenate amendment rates and by method of selenate application. Researchers conducted two experiments across Oregon, one with high and low Se amendment rates (900 vs. 90 g Se ha-1) and another with two forms of Se application (liquid foliar sodium selenate vs. granular slow-release Selcote Ultra) applied at 0, 45 and 90 g Se ha-1. The high amendment rate (900 g Se ha-1) resulted in 6.4× higher forage Se concentrations in the first cut (49.19 vs. 7.61 mg Se kg−1 plant DM, respectively) compared with the 90 g ha−1 amendment rate, indicating that forages can tolerate higher selenate amendment rates. Most of the Se was incorporated as SeMet (75%), and only a limited amount was stored in the selenate reserve pool in the leaves. The higher application rate of selenate amendment increased forage Se concentrations in the first and second cuts, but carry over in the subsequent year was negligible. The application of foliar selenate or the granular soil amendment both resulted in a linear, dose-dependent increase in forage Se concentration. The first-cut forage Se concentrations were higher with foliar selenate amendment, but second, third and residual (following spring) cut forage Se concentrations were higher with granular soil amendment. Given the linear relationship between forage Se concentrations and whole-blood Se concentrations in livestock consuming Se-biofortified forage, we conclude that targeted grazing or other forage feeding strategies will allow producers to adapt to either selenate-amendment form. See Reference 34.

Selenium uptake by different types of forage was studied in Western Oregon as part of a larger study. Sodium selenate was foliar applied at 0 and 45 g Se ha-1 to plots of alfalfa, birdsfoot trefoil, red clover, sainfoin and chicory as monocultures and intercropped with either subterranean clover or balansa clover. Chicory was most responsive to Se-fertilization in the two-year project, with a higher concentration of Se than other perennial species. In year one, birdsfoot trefoil and red clover were intermediate, whereas alfalfa had the lowest Se concentration after Se amendment. By year two, alfalfa and birdsfoot trefoil were intermediate and red clover was lowest in Se concentration. Despite having lower annual dry matter yields, both chicory and birdsfoot trefoil provided quantities of Se similar to that of alfalfa and more than or equal to that of red clover on a per-acre basis. See Reference 38.

Research and references

The following research findings may be useful to Oregon livestock producers. Many of these studies have been conducted at Oregon State University.

General science

Muth, 0. H. White muscle disease, a selenium-responsive myopathy: Journal of American Veterinary Medical Association.1963. v. 142, p. 272-277.

Swecker, W.S. and R.J. Van Saun (eds). Trace Minerals in Ruminants, Veterinary Clinics of North America: Food Animal Practice 2023; 39(3) (https://doi.org/10.1016/j.cvfa.2023.08.011).

Beef

1. Hall, J.A., G. Bobe, W.R. Vorachek, H. Hugejiletu, M.E. Gorman, W.D. Mosher, and G.J Pirelli. Effects of feeding selenium-enriched alfalfa hay on immunity and health of weaned beef calves. Biological Trace Element Research. 2013; 156:96–110. https://doi.org/10.1007/s12011-013-9843-0.

2. Hall, J.A., G. Bobe, J.K. Hunter, W.R. Vorachek, W.C. Stewart, J.A. Vanegas, C.T. Estill, W.D. Mosher, G.J. Pirelli. Effect of feeding selenium fertilized alfalfa hay on performance of weaned beef calves. PLoS ONE. 2013; 8(3):e58188. https://doi.org/10.1371/journal.pone.0058188.

3. Hall, J.A., A.M. Harwell, R.J. Van Saun, W.R. Vorachek, W.C. Stewart, M.L. Galbraith, K.J. Hooper, J.K. Hunter, W.D. Mosher, G.J. Pirelli. Agronomic biofortification with selenium: Effects on whole blood selenium and humoral immunity in beef cattle. Animal Feed Science and Technology. 2011; 164:184–190. https://doi.org/10.1016/j.anifeedsci.2011.01.009.

4. Hall, J.A., G. Bobe, W.R. Vorachek, C.T. Estill, W.D. Mosher, G.J. Pirelli, M. Gamroth. Effect of supranutritional maternal or colostral selenium supplementation on passive absorption of immunoglobulin G in selenium-replete dairy calves. Journal of Dairy Science. 2014; 97(7): 4379-91. https://doi.org/10.3168/jds.2013-7481.

5. Hall, J.A., G. Bobe, W.R. Vorachek, K. Kasper, M.G. Traber, W.D. Mosher, G.J. Pirelli, M. Gamroth. Effect of supranutritional organic selenium supplementation on postpartum blood micronutrients, antioxidants, metabolites, and inflammation biomarkers in selenium-replete dairy cows. Biological Trace Element Research. 2014; 161(3): 272- 87. https://doi.org/10.1007/s12011-014-0107-4.

6. Wallace, L.G., G. Bobe, W.R. Vorachek, B.P. Dolan, C.T. Estill, G.J. Pirelli, J.A. Hall. Effects of feeding pregnant beef cows selenium-enriched alfalfa hay on selenium status and antibody titers in their newborn calves. Journal of Animal Science. 2017; 95(6):2408–2420. https://doi.org/10.2527/jas2017.1377.

7. Hall, J.A., A. Isaiah, C.T. Estill, G.J. Pirelli, J.S. Suchodolski. Weaned beef calves fed selenium-biofortified alfalfa hay have an enriched nasal microbiota compared with healthy controls. PLoS ONE. 2017; Jun 8; 12(6): e0179215. https://doi.org/10.1371/journal.pone.0179215.

8. Apperson, K.D., W.R. Vorachek, B.P. Dolan, G. Bobe, G.J. Pirelli, J.A. Hall. Effects of feeding pregnant beef cows selenium-enriched alfalfa hay on passive transfer of ovalbumin in their newborn calves. Journal of Trace Elements in Medicine and Biology. 2018; Dec; 50: 640-645. https://doi.org/10.1016/j.jtemb.2018.05.014.

9. Hall, J.A., A. Isaiah, G. Bobe, C.T. Estill, J.K. Bishop-Stewart, T.Z. Davis, J.S. Suchodolski, G.J. Pirelli. Feeding selenium-biofortified alfalfa hay during the preconditioning period improves growth, carcass weight, and nasal microbial diversity of beef calves. PLoS ONE. 2020; Dec 1; 15(12): e0242771. https://doi.org/10.1371/journal.pone.0242771.

10. Diniz, W.J.S., G. Bobe, J.J. Klopfenstein, Y. Gultekin, T.Z. Davis, A.K. Ward, J.A. Hall. Supranutritional maternal organic selenium supplementation during different trimesters of pregnancy affects the muscle gene transcriptome of newborn beef calves in a time-dependent manner. Genes. 2021; 12(12):1884. https://doi.org/10.3390/genes12121884.

11. Hall, J.A., A. Isaiah, E.R.L. McNett, J.J. Klopfenstein, T.Z. Davis, J.S. Suchodolski, G. Bobe. Supranutritional selenium-yeast supplementation of beef cows during the last trimester of pregnancy results in higher whole-blood selenium concentrations in their calves at weaning, but not enough to improve nasal microbial diversity. Animals. 2022, 12, 1360. https://doi.org/10.3390/ani12111360.

12. Herdt, T.H. and B. Hoff. The use of blood analysis to evaluate trace mineral status in ruminant livestock. Veterinary Clinics of North American Food Animal Practice. 2011; 27, 255–283. https://doi.org/10.1016/j.cvfa.2011.02.004.

13. Spears, W., V. L. N. Brandao, and J. Heldt. NUTRITION: Invited Review: Assessing trace mineral status in ruminants, and factors that affect measurements of trace mineral status. Applied Animal Science. 2022; 38:252–267. doi:10.15232/aas.2021-02232. https://doi.org/10.15232/aas.2021-02232.

14. Diniz, W.J.S., G. Bobe, J.J. Klopfenstein, J.D. Remy, T.Z. Davis, and J.A. Hall. Supranutritional selenomethionine during different trimesters of gestation in beef cows benefits gene expression in monocytes at parturition. In preparation for Genes.

15. Hall, J.A., G. Bobe, W.R. Vorachek, J.J. Klopfenstein, I.O. Thompson, C.L. Zurita-Cruz, B.P. Dolan, L. Jin, T.Z. Davis. Effects of supranutritional selenium supplementation during different trimesters of pregnancy on humoral immunity in beef cattle at the time of parturition. Biological Trace Element Research. 2024, https://doi.org/10.1007/s12011-024-04457-1

Sheep and goats

16. Sánchez, J., P. Montes, A. Jiménez, S. Andrés. Prevention of clinical mastitis with barium selenate in dairy goats from a selenium-deficient area. Journal of Dairy Science. 2007; 90:2350–2354. https://doi.org/10.3168/jds.2006-616.

17. Hall, J.A., R.J. Van Saun, T. Nichols, W. Mosher, G. Pirelli. Comparison of selenium status in sheep after short-term exposure to high-selenium fertilized forage or mineral supplement. Small Ruminant Research. 2009; 82:40–45. https://doi.org/10.1016/j.smallrumres.2009.01.010.

18. Hall, J.A., D.P. Bailey, K.N. Thonstad, R.J. Van Saun. Effect of parenteral selenium administration to sheep on prevalence and recovery from footrot. Journal of Veterinary Internal Medicine. 2009; 23:352–358. https://doi.org/10.1111/j.1939-1676.2008.0253.x.

19. Hall, J.A., R.S. Sendek, R.M. Chinn, D.P. Bailey, K.N. Thonstad, Y. Wang, N.E. Forsberg, W.R. Vorachek, B.V. Stang, R.J. Van Saun, G. Bobe. Higher whole blood selenium is associated with improved immune responses in footrot-affected sheep. Veterinary Research. 2011; 42:99. https://doi.org/10.1186/1297-9716-42-99.

20. Hall, J.A., R.J. Van Saun, G. Bobe, W.C. Stewart, W.R. Vorachek, W.D. Mosher, T. Nichols, N.E. Forsberg, G.J. Pirelli. Organic and inorganic selenium: I. Oral bioavailability in ewes. Journal of Animal Science. 2012; 90:568–576. https://doi.org/10.2527/jas.2011-4075.

21. Stewart, W.C., G. Bobe, W.R. Vorachek, G.J. Pirelli, W.D. Mosher, T. Nichols, R.J. Van Saun, N.E. Forsberg, J.A. Hall. Organic and inorganic selenium: II. Transfer efficiency from ewes to lambs. Journal of Animal Science. 2012; 90:577–584. https://doi.org/10.2527/jas.2011-4076.

22. Stewart, W.C., G. Bobe, G.J. Pirelli, W.D. Mosher, J.A. Hall. Organic and inorganic selenium: III. Ewe and progeny performance. Journal of Animal Science. 2012; 90:4536–4543. https://doi.org/10.2527/jas.2011-5019.

23. Stewart, W.C., G. Bobe, W.R. Vorachek, B.V. Stang, G.J. Pirelli, W.D. Mosher, J.A. Hall. Organic and inorganic selenium: IV. Passive transfer of immunoglobulin from ewe to lamb. Journal of Animal Science. 2013; 91:1791–1800. https://doi.org/10.2527/jas.2012-5377.

24. Hugejiletu, H., G. Bobe, W.R. Vorachek, M.E. Gorman, W.D. Mosher, G.J. Pirelli, J.A. Hall. Selenium supplementation alters gene expression profiles associated with innate immunity in whole blood neutrophils of sheep. Biological Trace Element Research. 2013; 154:28–44. https://doi.org/10.1007/s12011-013-9716-6.

25. Hall, J.A., W.R. Vorachek, W.C. Stewart, M.E. Gorman, W.D. Mosher, G.J. Pirelli, G. Bobe. Selenium supplementation restores innate and humoral immune responses in footrot-affected sheep. PLoS ONE. 2013; 8(12):e82572. https://doi.org/10.1371/journal.pone.0082572.

26. Hall, J.A., G. Bobe, B.K. Nixon, W.R. Vorachek, H. Hugejiletu, T. Nichols, W.D. Mosher, G.J. Pirelli. Effect of transport on blood selenium and glutathione status in feeder lambs. Journal of Animal Science. 2014; 92(9): 4115-22. https://doi.org/10.2527/jas.2014-7753.

27. Hooper, K.J., G. Bobe, W.R. Vorachek, J.K. Bishop-Stewart, W.D. Mosher, G.J. Pirelli, M.L. Kent, and J.A. Hal. Effect of selenium yeast supplementation on naturally acquired parasitic infection in ewes. Biological Trace Element Research. 2014; 161(3): 308-17. https://doi.org/10.1007/s12011-014-0134-1.

28. Galbraith M.L., W.R. Vorachek, C.T. Estill, P.D. Whanger, G. Bobe, T.Z. Davis, and J.A. Hall. Rumen microorganisms decrease bioavailability of inorganic selenium supplements. Biological Trace Element Research. 2016; 171: 338-343. https://doi.org/10.1007/s12011-015-0560-8.

Horses

29. Brummer, M., S. Hayes, S.M. McCown, A.A. Adams, D.W. Horohov, and L.M. Lawrence. Selenium depletion reduces vaccination response in horses. Journal of Equine Veterinary Science. 2011; 31:250-356. https://doi.org/10.1016/j.jevs.2011.03.074.

30. Brummer, M., S. Hayes, A.A. Adams, D.W. Horohov, K.A. Dawson, and L.M. Lawrence. The effect of selenium supplementation on vaccination response and immune function in adult horses. Journal of Animal Science. 2013; 91:3702-3715. https://doi.org/10.2527/jas.2012-5819.

31. NRC. Nutrient Requirements of Horses. 6th rev. ed. Washington, DC: National Academy Press. 2007; pp 94-97.

32. Pitel, M.O., E.C. McKenzie, J.L. Johns, and R.L.Stuart Influence of specific management practices on blood selenium, vitamin E, and beta-carotene concentrations in horses and risk of nutritional deficiency. Journal of Veterinary Internal Medicine. 2020; 34(5):2132-2141. https://doi.org/10.1111/jvim.15862.

Forage

33. Wang, G., G. Bobe, S.J. Filley, G.J. Pirelli, M.G. Bohle, T.Z. Davis, G.L. Bañuelos, and J.A. Hall. Effects of springtime sodium selenate foliar application and NPKS fertilization on selenium concentrations and selenium species in forages across Oregon. Animal Feed Science and Technology. 2021; 276. https://doi.org/10.1016/j.anifeedsci.2021.114944.

34. Hall, J.A., G. Bobe, S.J. Filley, G.J. Pirelli, M.G. Bohle, G. Wang, T.Z. Davis, and G.L. Bañuelos. Effects of amount and chemical form of selenium amendments on forage selenium concentrations and species profiles. Biological Trace Element Research. 2023; https://doi.org/10.1007/s12011-022-03541-8.

35. Hall, J.A., G. Bobe, S.J. Filley, M.G. Bohle, G.J. Pirelli, G. Wang, T.Z. Davis, and G.L. Bañuelos. Impact of selenium biofortification on production characteristics of forages grown following standard management practices in Oregon. Frontiers in Plant Science. 2023; 14:1121605. https://doi.org/10.3389/fpls.2023.1121605.

36. Filley, S.J., A. Peters, C. Bouska, G. Pirelli, and J. Oldfield. Selenium fertilization of pastures for improved forage selenium content. The Professional Animal Scientist. 2007; 23, 144-147. https://doi.org/10.15232/S1080-7446(15)30954-2.

37. Filley, S.J., G. Wang, J. Hall, G. J. Pirelli, M. G. Bohle, S. Ates, and T.Z. Davis. Selenium and fertilizer application schemes in hay fields. Sustainable Meat and Milk Production from Grasslands. 2018; 23, 185-187. https://www.europeangrassland.org/fileadmin/documents/Infos/Printed_Matter/Proceedings/EGF2018.pdf.

38. Seeno, E., J. MacAdam, A. Melathopoulos, S. Filley, and S. Ates. Management of perennial forbs sown with or without self-regenerating annual clovers for forage and nectar sources in a low-input dryland production system. Grass and Forage Science. 2023; 78, 462-479. https://doi.org/10.1111/gfs.12640.

Acknowledgments

The authors would like to thank Dr. Bret Taylor (research animal scientist, USDA Agricultural Research Service, Dubois, Idaho) and Dr. Robert Van Saun, DVM (Extension veterinarian, Penn State) for their technical review and assistance in preparing the original and revised versions of this publication.

About the authors

Shelby Filley

Professor, Animal and Rangeland Science, Area Livestock and Forages Faculty

Hayley White

Extension Forages and Livestock Assistant Professor of Practice

Gene Pirelli

Academic Wage Appointment, Animal and Rangeland Sciences (Emeritus)

Jean A. Hall

Professor, Biomedical Sciences, Carlson College of Veterinary Medicine

Oregon State University

This piece is part of the collection Forage Resources

OSU Extension Service

Selenium supplementation strategies for livestock in Oregon