In sheep up to 15 months of age selenium deficiency can manifest as slow growth and poor wool production, non specific signs of deficiency.
It may cause infertility in ewes and poor sperm motility in rams, and have an adverse effect on the immune system, meaning other diseases are more likely.
Clinical effects include white muscle disease in new born lambs or lambs 3-6 weeks old, but clinical disease is rarely seen now in New Zealand.
How do they become deficient?
30% of New Zealand’s pasture will not provide adequate levels of selenium to grazing animals. Plant level of selenium is dependent on soil level, though some plants are better absorbers than others – legumes tend to be lower in selenium than grasses.
Soil acidity (pH) and rainfall are also important factors that can affect selenium levels; alkaline soils encourage the absorption of selenium into the plant while selenium soil concentrations are lowest in spring when rainfall is highest.
Selenium levels can be checked by testing either blood or liver samples.
Prevention of deficiency
Drench: Many anthelmintics contain selanised drench, and this is the simplest way of supplementing young animals. Six weekly treatments are ideal. If dosing adults, four weeks prior to mating, then four weeks prior to lambing will protect lambs to docking.
Injectable: Treating ewes premating with a long-acting product will mean lambs don’t need treating until weaning.
Intraruminal boluses: These can protect for 3-4 months and have other elements also.
Topdressing with selenium prills in autumn will also provide sufficient selenium from mating to docking.
Take care as toxicity can occur- stick to the dose rate described!
Subclinical Cobalt (B12) deficiency
Signs of cobalt deficiency include poor growth, low appetite, pale gums, watery eye discharge and increased lamb loss at lambing. This used to be called ‘bush sickness’. Lambs are the most susceptible, then adult sheep, then calves.
What is the difference between cobalt and B12?
Cobalt is an essential component of Vitamin B12, which is made in the rumen by bacteria. Vitamin B12 is then absorbed into the blood stream in the small intestine, and stored in the liver.
How do they become deficient?
13% of New Zealand’s pasture will not provide adequate levels of cobalt to grazing animals. Sheep grazing pasture with cobalt concentrations <0.08mg/kg DM will become deficient.
Vitamin B12 Blood or liver samples will both give good indications of B12 status, pasture cobalt concentration is a less accurate predictor of vitamin B12 status since soil contamination can increase “pasture” cobalt concentrations.
Options for preventing deficiency include:
Treating lambs with vitamin B12 as an injection given subcutaneously in the neck region once at docking. The products available are Smartshot which lasts three to four months or up to eight months depending on dose amount, or Prolaject B12 which lasts four to six weeks.
Treating the ewes during late gestation with Prolaject gives a period of three to four weeks protection to their lambs, while Smartshot if given at mating lasts 10 months in the ewe and protects the lambs until a month old.
Topdressing with cobalt sulphate annually in the spring; please note that this approach is unsatisfactory on some soils because high manganese (Mn) levels can interfere with cobalt uptake by plants. From a management point of view, pasture must not be grazed for at least four weeks to allow the cobalt to be ‘washed’ into the soil and taken up by the pasture.