Selenium

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1. Se deposited from emissions as declined with the decrease in the use of coal as a fuel

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1. Use of ammonium sulphate fertiliser may reduce selenium uptake by lowering soil pH- Se is more available on higher pH soils

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1. Severe deficiency can cause respiratory distress and death of the animal. Deficiency may also reduce fertility and increase abortions.

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1. Both Selenate and selenite can be absorbed and translocated throughout the plant

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1. Both Se 4+ and Se 6+ can act as S analogues

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1. Inside the plant Se6+ moves unchanged to the leaves, Se 4+ is converted to inorganic Se 6+ and organic Se compounds prior to translocation

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1. Selenate can oxidise to selenite in a few weeks in soil

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1. Selenate is more readily leached than selenite

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1. standard rate 10g Se/ha depending on soil/tissue analysis

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Selenium in the UK

Changes in fossil fuel usage from coal to gas and oil have resulted in long term reductions in the atmospheric input of Se to herbage inthe UK. The increasing grain yield also has a tendency to dilute the level ofSe. The atmosphere is identified as playing an important role in the balance of Se in grassland ecosystems, potentially governing the critical levels for grazing livestock. ( Haygarth, Fowler, Sturup, Davison, Jones)

Application of sulphur-containing materials e.g. sulphate of ammonia or gypsum, can reduce the levels of Se in herbage. In a cutting trial in Co. Meath, heavy applications of gypsum (12 tonnes/ac) reduced herbage Se from 18 to 2 mg/kg DM. Sulphate of ammonia (1 tonne/ac) reduced herbage Se from 10 to 1.4 mg/kg DM. Sulphate of ammonia probably acts in three ways: dilution effect from increased grass growth; SO₄^2-/SeO₄^2- antagonism and NH₄⁺/SeO₄^2- antagonism

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Pastures may become Se deficient as a result of grazing management. Deficiency occurs when animal ingestion and absorption exceeds the rate of endogenous excretion (ca 100 days half life). For example if young lambs are removed from pasture at ages less than 100 days, then equilibrium between gut Se absorption and endogenous excretion will not have been achieved(animal is in a state of net Se accumulation) and removal of the animal to market will result in a net loss of Sefrom the grassland.

Pasture deficiency is also exacerbated by high stocking rates or grazing by larger animals with high rates of ingestion. Losses will also occur by removal of animal products such as sheep wool or cows milk.

Since levels of Se in UK wheat are generally low feed containing grain from the UK is also likely to be deficient in Se unless supplements are added

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Selenium deficiency in feed or food crops can be overcome by the addition of Se to fertilisers, studies being done in New Zealand, Denmark and Finland. The fertilisation practices have proved both effective and safe and have led to widespread application (with government support) in both New Zealand and Finland

The addition of Se to fertiliser ensures sheep do not require individual handling and do not escape treatment. Free choice feeding of mineral salt supplements generally results in non-uniform dosage with some animals receiving insufficient Se. Application in fertiliser also ensures that young livestock in Se deficient areas are protected throughout their early life.

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There is no apparent accumulation of toxic amounts of selenium occurring from the use of Se amended fertilisers. No build €“up has been found in New Zealand where Se has been added to fertilisers for 20 years

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Selenium fertilisers do not have to be applied evenly to the paddock as the sheep will graze across the area and ingest Se treated grass.

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Work in New Zealand and Australia has shown that application of 5-10g/ha Se as sodium selenate elevates forage Se to levels acceptable for animal health

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Selenium deficiency causes white Muscle disease (stiff lamb disease). This affects cattle, sheep, goats, pigs, horses and poultry.

Severe deficiency can affect the respiratory muscles causing respiratory distress and death of the animal.

Degeneration may affect the heart can result in sudden death of the animal.

Deficiency may also reduce fertility and increase abortions. It also causes stillbirth and embryonic resorption in sheep.

General disease resistance may be reduced

Symptoms usually develop progressively but Selenium deficiency generally causes reduction in productivity of livestock and ill-thrift

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TEAGASCPhilip A M Rogers

3 categories of cattle (cull dairy cows, cull beef cows, finished cows)

This report concludes that

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Irish vet journal 1990

Rogers, Arora, Fleming, Crinion, McLaughlin

Se toxicity occurs in counties Dublin, Limerick, Meath and Tipperary. Se toxic soils also occur in Carlow, Kerry and Kilkenny. Toxicity is uncommon but deficiency is very common

Supplements high in Se should not be given to livestock within 5km of known toxic farms unless blood samples from the stock are found to be low in Se

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Highest levels of soil Se are found in high pH low-lying peaty swamps Se toxic herbage is less palatable to stock

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Location of Se-toxic soils in Ireland

The location of Se-toxic soils is sporadic. Most are in Counties Carlow, Dublin, Kerry, Kilkenny, Limerick, Meath and Tipperary. Most affected farms are also high in Mo. Mo-induced copper deficiency is common in cattle on these farms. Small areas extend eastward from south Co. Limerick, through Clonmel (south Co. Tipperary) to Piltown (Co. Kilkenny). These are related to sporadic pockets of Namurian shale deposits, which influence soils in the immediate vicinity. However, the high-Se soils near Piltown are not molybdeniferous. This is the only instance of a seleniferous but not molybdeniferous soil known to date in Ireland.

Co. Carlow: near Castletown.

Co. Dublin: Pockets of high-Se, high-Mo soils from Namurian black shale occur near Garristown.

Co. Kerry: near Ardfert.

Co. Kilkenny: near Piltown.

Co. Limerick: The area between Foynes and Ardagh contains high Se, high Mo soils from the Clare shale.

Co. Meath: Many fields in the flood plain of the Skane river are Se-toxic. Stock in the Dunsany-Warrenstown area have shown sporadic signs of Se-toxicity for decades and similar signs were noted in stock in the area more than 100 years ago (Fream 1890). Mo-induced copper deficiency is common in the area also. Other Se-toxic areas occur in localised fields south of the Boyne and Blackwater rivers near Athboy, Navan, Slane, Drogheda, Dunshaughlin, Grange and Trim.

Co. Tipperary: near Boulick, Clonmel, Clogheen, and Rathronan.

There may be a few other locations, as yet unknown

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Concentration of Se in grain throughout the UK is in the region of 0.013-0.018mg/kg whereas levels in the US are reported to be 0.37-0.45 mg/kg

Changes in fossil fuel usage from coal to gas and oil have resulted in long term reductions in the atmospheric input of Se to herbage in the UK. The increasing grain yield also has a tendency to dilute the level of Se. The atmosphere is identified as playing an important role in the balance of Se in grassland ecosystems, potentially governing the critical levels for grazing livestock. ( Haygarth, Fowler, Sturup, Davison, Jones)

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Application of sulphur-containing materials e.g. sulphate of ammonia or gypsum, can reduce the levels of Se in herbage. In a cutting trial in Co. Meath, heavy applications of gypsum (12 tonnes/ac) reduced herbage Se from 18 to 2 mg/kg DM. Sulphate of ammonia (1 tonne/ac) reduced herbage Se from 10 to 1.4 mg/kg DM. Sulphate of ammonia probably acts in three ways: dilution effect from increased grass growth; SO₄^2-/SeO₄^2- antagonism and NH₄⁺/SeO₄^2- antagonism

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Pastures may become Se deficient as a result of grazing management. Deficiency occurs when animal ingestion and absorption exceeds the rate of endogenous excretion (ca 100 days half life). For example if young lambs are removed from pasture at ages less than 100 days, then equilibrium between gut Se absorption and endogenous excretion will not have been achieved(animal is in a state of net Se accumulation) and removal of the animal to market will result in a net loss of Se from the grassland.

Pasture deficiency is also exacerbated by high stocking rates or grazing by larger animals with high rates of ingestion. Losses will also occur by removal of animal products such as sheep wool or cows milk.

Since levels of Se in UK wheat are generally low feed containing grain from the UK is also likely to be deficient in Se unless supplements are added

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1. <!--[if gte vml 1]> Addition of Se to Fertiliser Effects on Livestock
   
   1. current national inputs of Cu, I and Se are inadequate to maintain normal trace element status in finished steers and cull (especially beef) cows at slaughter, and
   2. current national inputs of Cu, I and Se are inadequate to maintain normal trace element status in finished steers and cull (especially beef) cows at slaughter, and
   3.  
   4. Cattle at risk of trace element deficiencies include all dairy and suckler cows, and beef animals fed unsupplemented forages (pasture, silage, hay or straw).
2. <!--[if gte vml 1]> Addition of Se to Fertiliser Effects on Livestock
   
   1. current national inputs of Cu, I and Se are inadequate to maintain normal trace element status in finished steers and cull (especially beef) cows at slaughter, and
   2. current national inputs of Cu, I and Se are inadequate to maintain normal trace element status in finished steers and cull (especially beef) cows at slaughter, and
   3. Cattle at risk of trace element deficiencies include all dairy and suckler cows, and beef animals fed unsupplemented forages (pasture, silage, hay or straw).

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