Selenium deficiency has been associated with a range of disorders in grazing animals. In its most serious form it causes white muscle disease, a myopathy which affects kids, lambs, calves and foals in some higher rainfall areas of Victoria.
Selenium deficiency has also been associated with illthrift and poor wool growth in sheep and reduced resistance to disease in a number of species.
In New Zealand, selenium supplementation has resulted in significant improvements in lambing performance in low selenium areas. Similar responses have not been observed in a number of trials in Victoria.
Other factors are significant in the induction of white muscle disease: stress, mustering, increased levels of unsaturated fatty acids in spring pastures and poor vitamin E nutrition have been directly involved. Both selenium and vitamin E have roles in the prevention of muscle damage by oxidants produced during metabolism. White muscle disease occurring in weaner lambs grazing cereal stubbles, or dry autumn pastures, is responsive to vitamin E but not selenium supplements.
Low selenium areas of Victoria include the acid oils on and about the Great Dividing Range, particularly the Central Highlands, and the high rainfall areas of the west and south-east coastal fringe. It must be emphasized that selenium nutrition is subject to marked variation between years, between seasons, and even between soil types within farms and paddocks: specific regional information is available from your State Department of Agriculture Offices. Selenium deficiency can be prevented by a range of treatments.
Drenches and Injections: Kids affected with white muscle disease are treated with intramuscular injections or oral drenches of selenium. Selenium injections can be administered with pulpy kidney-tetanus vaccines and mixed preparations have been registered commercially for use in sheep, but not as yet in goats.
Selenium can also be combined with some worm drenches. It is wise to check compatibility with the drench manufacturers and these mixtures should always be used immediately. It is important that an assessment of selenium nutrition be made before animals are treated because selenium compounds are toxic. Selenium in excess is a poison and is therefore obtained only on veterinary prescription.
All breeds of sheep and goats are suceptible to White Muscle Disease (WMD) an example for the Disease
Bullets: Selenium bullets are administered to individual animals, lodge in the rumen and should provide the small requirements of selenium for the life of the animal. However, some batches of commercial bullets were shown to provide adequate selenium for only a few months.
Topdressing: A mixture of selenium and superphosphate from Pivot Fertilizers, Selecote, has now been registered for use in Victoria and similar products may be available from your fertilizer supplier. This has proved a useful alternative method of supplementing grazing livestock in low selenium areas.
SelenIum in the fertilizer is encapsulated within water-soluble prills, which readily break down upon application to pasture. Selenium priIls penetrate the pasture canopy and must be absorbed back through the root system to increase herbage selenium concentrations.
With the registered fertilizer mixtures there is very little possibility of animals receiving a toxic dose. The continual supply of organic selenium for 6 months, combined with reserve capacity of body tissues ensures adequate selenium nutrition for 12 months with the fertilizer; selenium drenches and vaccines are only effective for around 3 months.
Selenium deficiency mostly affects young animals in spring. It is therefore recommended that the fertilizer application be timed so as to optimise the selenium nutrition of these animals; an autumn application will benefit the developing foetus and ensure protection during spring.
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