The Role of Selenium Yeast in
Ruminant Feeding Programs

 

In livestock, selenium (Se) deficiency appears to compromise immune function and is associated with a higher incidence of health-related problems including mastitis, retained fetal membranes, uterine infections, cystic ovaries, and poor conception rates. In some geographic areas, marginal soil Se concentrations can result in Se deficiency, even when rations are fortified with 0.3 ppm of supplemental Se, the FDA maximum inclusion level.

Selenium yeast (Se-yeast) has recently received FDA approval as a source of supplemental Se for beef and dairy cattle. Numerous suppliers have suggested Se-yeast has a higher biological availability than the industry's universal inorganic Se source, sodium selenite. The cost of Se-yeast could be at least 10 times greater than that of inorganic Se. For example, complete replacement of supplemental inorganic Se with Se-yeast increases ration cost about $2.00 per ton of treated feed or about 4¢ per cow per day. Because of the high cost of Se-yeast as a Se source, its biological and economic benefit must be evaluated carefully for each livestock operation.

The Biological Role of Selenium and the Bioavailability of Selenium Sources
The most consistent biological response to enhanced Se status in animals is improved immune function. Improved immune function can result in lower metabolic problems, as mentioned previously. The source of Se supplementation is unlikely to produce significant growth or milk yield responses and production studies are usually insensitive to improved Se status of growing or lactating ruminants.

Many organic trace minerals (e.g., chelates, proteinates) have higher bioavailabilities than their inorganic counterparts. It is logical to assume organic Se would also have higher bioavailability compared with inorganic Se. However, Se has very specific biological roles that must be considered when measuring relative bioavailability of Se sources. There are a number of functional selenoproteins in the body but only the selenoenzyme, glutathione peroxidase (GSH-Px), has a nutritionally meaningful role in metabolism. Blood GSH-Px activity or whole blood Se is commonly used to detect bioavailability differences among Se sources. The assumption for these methods is that organic Se (e.g., Se-methionine) is more "bioavailable" compared with inorganic Se.

Under normal dietary conditions, sodium selenite is readily absorbed, converted to Se-cysteine, and then incorporated into the GSH-Px enzyme. In contrast, supplemental Se-methionine is stored as body protein and later extracted for further conversion to Se-cysteine. This is a multi-step process that generally slows the movement of Se to GSH-Px. Data exist showing that, across livestock species maintained in typical production situations, feeding sodium selenite and Se-yeast result in similar blood GSH-Px activity. Weiss (2002) suggested that in typical dairy rations, Se in Se-yeast may be about 20% more available for promoting GSH-Px activity than Se from sodium selenite.

About 65% of the Se in Se-yeast is in the form of Se-methionine. When Se-yeast is fed, the body uses Se-methionine as a source of methionine for body protein synthesis. Enrichment of meat and milk proteins with Se when Se-yeast is fed can have useful production implications but this does not necessarily indicate higher bioavailability. Se enrichment of milk occurs when Se-yeast is fed because Se-methionine is used as a methionine source for protein synthesis. Weiss (2003) summarized nine studies with lactating ruminants and reported that milk Se concentration was 1.18 times greater when animals were fed Se-yeast compared with inorganic Se.

Conditions Where Selenium Yeast May Be Beneficial
Safety and Regulatory Restrictions: Certain markets do not permit the use of inorganic Se. In addition, because Se-methionine is primarily directed toward deposition in body tissues, Se-yeast will be much less likely than sodium selenite to result in toxicity to the animal if excess Se is consumed.

Presence of Dietary Antagonists: Considerable evidence shows certain dietary antagonists may reduce the availability of sodium selenite in ruminants. This may become important when supplemental mineral intake is low and in low soil-Se geographies. Sulfur is the most important antagonist in ruminants and has been shown to result in linear decreases in Se digestibility from inorganic Se, when sulfur concentrations were within ranges typically encountered.

Increasing Selenium in Key Tissues: Increasing Se concentration in the proteins of fetal tissues and in colostral milk may yield health benefits. As such, there should be measurable benefits to including Se-yeast in the diets of animals during gestation and early lactation.

Economic Analysis and Recommended Usage Rates for Se-Yeast
Complete replacement of supplemental Se from inorganic Se with Se-yeast increases ration cost about $2.00 per ton of treated feed or about 4¢ per dairy cow per day. Cost for beef cattle would be about 2.6¢ per day because of lower feed intake levels. Assuming a possible 20% greater GSH-Px activity when Se-yeast is fed compared with inorganic Se, complete replacement of inorganic Se with Se yeast is probably not cost-effective, even considering FDA limits on supplemental Se.

The ADM technical service staff offers the following suggestions for optimizing usage of organic Se from Se-yeast in ruminant diets:

  • Total dietary Se must not exceed the FDA maximum of 0.3 ppm. There seems to be a consensus among Se-yeast suppliers that 50% replacement of inorganic Se with Se-yeast may be an economically appropriate. As such, it is suggested that no more than 0.15 ppm of Se from Se-yeast be included in ruminant diets and that no more than 1 mg/day of supplemental Se as Se-yeast be included in beef rations and no more than 3 mg/day of supplemental Se be included in the rations of dairy cattle.
     

  • Late pregnant and early lactation animals will likely derive the highest economic benefit from the use of Se-yeast, because Se stores in the fetus and colostrum will also be increased with probable health benefits for the offspring.
     

  • Across all classes of growing and breeding livestock, Se-yeast should probably be restricted to only to those animals experiencing high stress with potentially low feed intake.
     

  • Vitamin E and Se have overlapping roles in cellular protection against the damaging effects of superoxides in the body. As such, a high level of diet fortification with vitamin E will likely offset some of the potential benefits of a more bioavailable Se source. For a cost that is equal to that of replacing 50% of the inorganic Se with Se-yeast, the level of supplemental vitamin E in the ration can be increased 3 to 5 times. In a dairy ration, for example, supplemental vitamin E could be increased from 1,000 to 3,000 IU per cow daily at equal cost to replacing 50% of the inorganic Se.

Differentiating Among the Selenium Yeast Products on the Market
Currently, there are at least five Se-yeast suppliers with products on the market. All of these products should be equally safe and all have FDA approval for use in animal feeds. It is the ADM position that, on the basis of equal Se-methionine levels, all of these products should have similar biological efficacy.

 

Suggested Maximum Feeding Rates for Se-Yeast

 

Se-Yeast, ppm
in ration

Se-Yeast, mg/day

Dairy

 

 

Calves

0.15

1

Heifers

-

-

Close-up Dry Cows

0.15

1 to 2

Lactating cows (<120 DIM)

0.15

3

Lactating cows (>120 DIM)

-

-

Beef

 

 

Brood cows (late gestation to breeding)

0.15

1 to 2

Stocker cattle

-

-

Feedlot cattle

 

 

Arrival period

0.15

1

Growing/finishing

-

-

 

 

 

For more information Call Toll Free 1-866-666-7626
or E-Mail us at AN_AnimalHealthTeam@adm.com

 

ADM Animal Nutrition, a division of Archer Daniels Midland Company