Vaccinations ineffective if selenium levels low
By Jonathan Long
INVESTING time and money in vaccination programmes may be a false economy when animals selenium levels are inadequate, says one Welsh vet.
Ian Jones, who is based in Newtown, Powys, says that when animals are selenium deficient they cannot gain the full benefits of vaccination programmes because their immune systems are compromised.
"Selenium has a large effect on the immune status of livestock. Animals with low levels of selenium will be more susceptible to infections than those with selenium levels," says Mr Jones.
Selenium deficiency also greatly reduces stocks reproductive ability. When cows lack selenium they do not bull or stand for service and fail to hold to service, consequently increasing the calving cycle and upsetting herd routine.
"In selenium-deficient herds calves will be slow to suckle, fail to thrive and are more susceptible to infections. Calves will be more prone to scour and calves which suffer from scours will be three times more likely to develop pneumonia," warns Mr Jones.
Suckler cows suffering from selenium deficiency are best treated with an injectable product, such as Deposel, which should guarantee that selenium levels are right for at least 12 months, says Mr Jones. "The best time to treat cows lacking selenium is mid pregnancy. This ensures both cow and calf receive adequate selenium and cows have sufficient selenium in their bloodstream at bulling."
Sheep producers are less likely to realise flocks have a selenium deficiency. Problems caused by a deficiency may be put down to other causes, such as a vaccine break down or poor nutrition.
"Sheep are less inclined to be treated, as symptoms are often masked by a number of factors, including the large numbers in which sheep are kept. A producer with one barren cow in 50 will notice, however, if 10 in 500 sheep are barren it may be ignored or dismissed for another reason."
But selenium deficiency in sheep will result in similar problems to cattle. Lambs will be weakly and more susceptible to infection, ewes will fail to cycle or hold to service and the flock may respond less well to vaccination programmes, says Mr Jones.
"All of these problems reduce flock profitability and result in under-performance. While treating sheep with an injectable product, such as Deposel, may be expensive, new evidence suggesting the treatment may cover sheep for two years, means it could be justifiable."
Selenium is often the fundamental building block on which health programmes should be built. Mr Jones believes flocks and herds with correct selenium levels will respond better to all health treatments and producers will see increases in prolificacy and lamb and calf survival. *