Dr Barry Patten B.V.Sc., PhD
Selenium is an essential trace mineral in sheep and cattle (Barragry 1994).
Oral selenium is absorbed mainly from the duodenum, absorbed selenium is carried in the plasma and undergoes a transformation in erythrocytes (Barragry 1994). Oral dosing, at a recommended dose of 0.1mg selenium per kilogram bodyweight, successfully combats selenium deficiency in the short term (Barragry 1994, Booth and McDonald). Some risk of toxicity is present if the dose of selenium is exceeded, more particularly when selenium is given by injection rather than by oral administration (Masters and White, 1996). The risk of toxicity of selenium in cattle is raised if parenteral treatment (selenium by injection) is used, where the toxic dose is 1.2mg/kg, whereas the toxic dose for oral administration is 9mg/kg. (Barragry 1994).
Sodium selenate and sodium selenite are widely used as short term selenium supplements and both are biologically available when given by oral or subcutaneous administration (Meads et al., 1980). In Australia mineralized anthelmintic drenches, containing cobalt, selenium and copper are marketed for use in sheep and for cattle . The recommended dose is 0.1mg of selenium as sodium selenate for sheep and 0.1mg/kg to 0.15mg/kg for cattle. Oral doses of selenium as sodium selenite or sodium selenate are absorbed rapidly by the animal and the effect may be from 2 weeks to 3 months (Hoskins et al., 1986, Tasker 1992).
Other forms of oral selenium supplements include long acting/sustained release intra-ruminal selenium pellets that provide 10g of elemental selenium that is absorbed over a 6 to 9 month period. Cattle can tolerate single doses of multiple selenium pellets without selenium toxicity (Judson and McFarlane 1984, Wilson et al., 1991).
A heavy pellet containing selenium was developed by CSIRO in 1967 by Kunckel and Buckley (CSIRO Rural Research 86; 19). The most effective pellet for sheep contained 5% elemental selenium (Kunckel and Buckley 1969).
The effectiveness of selenium intra-ruminal pellets has been demonstrated over several studies. Kunckel and Buckley (1969) showed that sheep administered 5% selenium pellets (10g gross weight) showed raised blood selenium levels at least twice the level of pre-treatment controls and the blood selenium levels remained high for at least 12 months post-treatment.
Judson et al., (1991) showed that 5% selenium pellets (10g gross weight) administered to sheep grazing selenium deficient pasture in South Australia showed raised blood selenium levels for up to 200 weeks. Lambs born from the treated ewes showed raised selenium levels for 4 to 6 months after birth (Judson et al., 1991). Langlands et al., (1990) showed that a 5% selenium pellet, especially when administered to sheep in conjunction with a metal grinder increased blood selenium levels for up to 2 years.
A 10% selenium pellet was later developed for cattle (Judson et al., 1980). Judson et al., (1980) demonstrated that 10% selenium pellets (30g gross weight) were effective in raising blood selenium levels in cattle grazing pasture for up to 18 months. Hidiroglou et al., (1985) showed that 30g 10% selenium pellets administered to cross-bred cows in Ontario Canada raised plasma selenium and blood glutathione peroxides levels in the treated cows and controlled muscular dystrophy in calves born from the treated cows.
Kunckel and Buckley (1969) showed no toxic effects over a 12-month period in sheep given 4 times the normal dose of selenium pellets (4 x 5% selenium pellets 10g gross each). Radositis Blood and Gay (1990) indicated that the average delivery of selenium from the 10g selenium pellet was 1mg/day indicating no danger of toxicity using the pellet in sheep. Donald et al., (1993) fed grazing sheep 10g gross weight selenium pellets containing 5%, 10% or 15% elemental selenium. The sheep were monitored for 4 years and showed no adverse effects from any of the selenium pellets.
Wilson et al., (1991) showed that 300-350kg growing cattle administered 2, 3 and 4 times the recommended dose of 10% selenium pellets (30g gross weight) showed no signs of toxicity and that selenium levels in tissues from these animals posed no risk to humans who may consume the tissue.
Barragry T., (1994) Veterinary Drug Therapy. Lea and Febiger USA.
Booth N.H., and McDonald L.E., Veterinary Pharmacology and Therapeutics 6th edition, Iowa State Univ. Press.
CSIRO A selenium pellet for sheep. Rural Research 86; 19-22.
Donald G.E., Langlands J.P., Bowles J.E., Smith A.J Burke G.L (1993) Selenium supplements for grazing sheep. 3. Development of an intra-ruminal pellet with an extended life. Animal feed Science and Technology 40: 295-308.
Hoskins W.J., Caple I.W., Halpin C.G., Brown A.J, Paynter D.I., Conley D.N., Northcoombes P.L., (1986), Trace Elements for Pasture and Animals in Victoria. Vic Govt Printing Office
Judson G.J., Mattschoss K.H., Clare R.J., (1980) Selenium pellets for Cattle Aust. Vet J 56: 304.
Judson G.J., and McFarlane J.D., (1984) Aust Vet J 61, 333
Judson G.J., Ellis N.J.S., Kempe B.R., Shallow M., (1991) Long-acting selenium treatments for sheep. Aust. Vet. J. 68: 263-265.
Kunckel R.R. and Buckley R.A., (1969) The provision of Selenium to Sheep by means of Heavy Pellets. Aust. J. agric. Res 20; 1099-1107.
Langlands J.P., Bowles J.E., Donald G.E., Smith A.J., (1990) Selenium supplements for grazing sheep 2. Effectiveness of intra-ruminal pellets. Animal Feed Science and Technology 28: 15-28
Masters D.G., White C.L (1996) Detection and Treatment of Mineral Nutritional Problems in grazing Sheep. ACIAR Australia.
Meads W.J., Osborn J., Grant A.B., (1980) New Zealand Veterinary Journal 28, 20-22
Radositis, Blood and Gay (1994) Diseases Caused by Deficiencies of Minerals: Selenium Veterinary Medicine pg 1423.
Wilson D.J., Norman B.B., Hird D.W., Wilson C.B., Oliver M.N., (1991) Amer J Vet Research 52, 1866-1870
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