Selenium deficiency, which often occurs in association with vitamin E deficiency, is a relatively common trace mineral deficiency in Ireland. Both selenium and vitamin E are important components of the animal’s antioxidant defence mechanisms.
Selenium is an essential component of glutathione peroxidise (GSH-Px), an enzyme which detoxifies lipid peroxides and limits the build-up of oxygen free radicals which can cause cellular destruction in the body.
Vitamin E plays a similar role in protecting cell membranes. Enormous quantities of free radicles can be produced in muscle during times of peak physical exertion, such as in calves running around a field following turnout.
If young calves, or lambs, are deficient in selenium, then there is a risk of severe muscular damage and the disease called ‘‘White Muscle Disease’’. Selenium also plays an important role in maintaining immune function and selenium deficiency has certainly been associated with immunosuppression.
Selenium deficiency can certainly lead to an increased incidence of retained placenta, a disease which has been shown to occur due to depression of the immune system around calving. There is also some evidence linking selenium deficiency to an increased susceptibility to mastitis and a moderate rise in somatic cell count (SCC) in dairy herds.
‘‘White Muscle Disease’’, or nutritional myopathy, mainly affects young, rapidly growing calves and lambs. This disorder occurs most commonly at 2-4 months of age but can occur in younger and older animals. Disease may occur in outbreaks with up to 15% of a group of susceptible animals affected and mortality rates can approach 100%.
The clinical symptoms seen with nutritional myopathy depend to a large extent on the muscles affected. If the heart muscle or muscles of respiration (breathing) are affected, then death can occur very suddenly.
Most commonly, it is the large muscle masses that are affected, i.e. the shoulder, gluteal or hamstring regions. Therefore, calves are most commonly found down in sternal recumbency (sitting up but not able to stand) but appear bright and alert, unlike with diseases such as Blackleg. On palpation, the affected muscles are usually firm and swollen. Affected animals also usually have an increased heart rate.
Selenium deficiency can be diagnosed by blood sampling animals from the at risk group, i.e. calves in the case of ‘‘White Muscle Disease’’ and dry cows in the case of a high incidence of retained placenta.
Measuring blood selenium will give a picture of the status of the individual animal on the day of testing, while measuring GSH-Px will give information about the selenium status of the animals over the previous number of weeks, which may be more valuable diagnostically.
Post mortem examination of animals that die will usually demonstrate a white discolouration of degenerative muscle in the affected areas.
In the face of an outbreak of ‘‘White Muscle Disease’’, all calves in the group should be treated with a single injection of vitamin E/selenium (Vitesel). In terms of the affected animals, if the heart or respiratory muscles are affected, then death is assured within hours despite treatment.
In severely affected cases, with involvement of large amounts of muscle, the prognosis may also be guarded. However, most moderately affected cases will cure in 2-5 days.
In herds where selenium deficiency has been diagnosed, dietary supplementation is necessary on an on-going basis to prevent further clinical disease.
Dry cows should be fed a mineral mix containing the recommended levels of selenium. Alternatively, selenium may be delivered to cows via boluses, injections of longacting barium selenate or via mineral licks.
During lactation and the breeding season, selenium may be supplemented in concentrates if boluses are not used on the farm. It is recommended to consult your veterinary practitioner, nutritionist or Teagasc adviser in order to obtain advice on trace element feeding, taking into account the type of diet and the level of production in each herd.
Source: Farmers Journal