Selenium Fertilization on Southwestern Oregon Pastures

By Amy Peters and Shelby Filley

OSU Extension Agents

CCES 207
September 1, 2005

Introduction

Selenium (Se) is an essential micronutrient for livestock. However, forages grown in southwestern Oregon are Se deficient due to the low Se content of the volcanic soils.

Deficiencies in dietary Se can have detrimental effects on livestock. White muscle disease is most commonly recognized, but other problems such as reproductive and production (weight gain) losses, as well as immune system dysfunction, can all impact efficient livestock production.

Selenium has commonly been supplemented in livestock through injections and mineral mixes. These strategies often do not provide adequate blood selenium levels for an extended amount of time and are expensive. Injections provide only short-term increases in Se blood levels (about 30 days) and animal consumption of mineral mixed is inconsistent. Mineral mixes commonly contain inorganic forms of selenium, which are poorly utilized by the animal.

Another way to supply Se to livestock is through the pasture plants. The plants take the inorganic Se and convert it to organic form. The animals easily utilize this. Plant materials and yeast extracts contain the organic form of Se, which is absorbed and utilized with greater efficiency compared to inorganic forms. The addition of Se to commercial fertilizers has been used successfully in countries outside of the United States for many years.

Pasture Se Trials in SW Oregon

Through experiments conducted by Oregon State University Extension Service, Se regulations now allow the use of Se as a commercial fertilizer addition. Selenium deficient pastures were fertilized with Se in the springtime. Levels of Se addition, pounds per acre, were 0 (control), 0.5, 1.0, and 2 lb of Se as selenite, and 0.5 lb of Se as selenate.  Pasture plots were sampled prior to grazing, whenever pasture height reached 10-12”, and analyzed for Se (years 1 and 2). The addition of Se as fertilizer increased selenium content in the forage. Pasture clippings showed adequate levels of Se for two years (Table 1).

Discussion and Conclusion

Se fertilization of pasture or hay ground increases Se content of forage for approximately two years. Although some Se levels in the pasture were high, animals grazing in that field for a short amount of time should have no detrimental effects.  Other studies in western Oregon have shown adequate blood Se levels by livestock grazing the Se enriched forage. Work at the Union Experiment Station showed that even lambs and calves from dams grazing the pasture had adequate blood selenium levels.  Selenium is consumed with each bite of pasture or hay. The Se is highly utilizable by the animals since it has been converted to the organic form, and provides adequate blood Se levels over a sustained period. Selenium applied with fertilizer is an effective way to provide adequate levels of dietary Se for livestock. 

Cost and Effectiveness

Selenium supplementation via forage fertilization is a very cost effective way to provide dietary Se to livestock. Selenium, as an added ingredient to fertilizer, is available commercially at a cost of about $2.50 per acre, with forage sustaining adequate levels of Se for approximately two years. In comparison, 30-day supplies of Se through injectables cost $0.325 per lamb, while mineral blocks cost about $0.077 and mineral mixes cost $0.05 per lamb (30-day supplies). So, costs for 100 sheep on 20 acres for two years would be $50 for selenium fertilizer, $780 for injectables, $185 for mineral blocks, and $120 for mineral mixes.  However, the different methods of supplementation differ in effectiveness of providing Se to the animals. Often, Se blood levels are deficient when livestock are supplemented through mineral block and premixes because they do not consume the required amount of the blocks, loose mineral mixes, or premixes. Selenium-enriched forage through fertilization sustains animal blood Se levels for a significantly extended period compared to these other methods.

Availability - where to get it

Some fertilizer dealers in western Oregon have Se available as part of a fertilizer mixture. The Se is a commercial preparation called Selcote. Selcote is a mixture of readily available Se along with encapsulated Se that is a slow-release Se. This way some Se is immediately available to the plant, while the remaining Se is available over an extended period of time.  Private producers are using this already and find improved Se levels in their livestock blood.

Precautions

Although Se is a required nutrient, it can also be toxic if consumed in large quantities. Researchers in eastern OR tested the possibility of toxicity in cattle receiving multiple methods of Se supplementation, including injections, and were found to have safe blood Se levels.  You should not provide other forms of supplemental Se if pastures are fertilized with Se every other year.  You should, however, continue to provide other minerals needed by the animals.  It is a good idea to include blood mineral level screenings during routine health exams on your livestock, not only for Se, but also for other required minerals.

Table 1. Pasture forage selenium concentrations compared to dietary requirements.

 

Average Forage Se (ppm)

Adequate Dietary Se Levels (ppm)

Toxic Dietary Se Level (ppm) Long Term

Treatment

Year 1

Year 2

 

0.1 – 0.3

 

3.0

Control

0.09

0.06

½ lb Se as Selenite

1.17

0.20

1 lb Se as Selenite

3.11

0.20

2 lb Se as Selenite

4.24

0.51

½ lb Se as Selenate

8.44

0.43

References

Hathaway, R., G. Pirelli, S. Paxton, and J. Oldfield.  2001.  Selenium fertilization of pastures.  Western Section, American Society of Animal Science.  Bozeman, Montana.

Pulsipher, G., R. Hathaway, W. Mosher, G. Pirelli, and T. DelCurto.  2004.  The effect of fertilizing with sodium selenite on selenium concentration of hay and drain water and serum selenium concentrations in beef heifers and calves.  Proceedings, Western Section, American Society of Animal Science, Vol. 55.

Nutrient Requirements of Beef Cattle. 7th Revised Edition. 1996. National Academy Press. Washington, D.C.

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