It’s elementary, dear friends

Deficiency of the trace elements cobalt, iodine, selenium, and copper are major factors in the raising of healthy livestock. Tom Ward writes.

Trace elements in animals, not in the soil, are the subject of this article although the two topics can be interrelated. It is not exhaustive in its scope and I caution against relying on it for onfarm decisions – consult your vet or other animal health professional before deciding on a course of action onfarm.

Cobalt essential

Cobalt is essential for the synthesis of vitamin B12. A deficiency of vitamin B12 prevents conversion of propionic acid to glucose, meaning energy cannot be ingested, causing appetite loss.

Symptoms are usually low growth rates and loss of appetite in lambs, and in some cases discharges from the eyes. It is often misdiagnosed as worms.

Deficiency tends to occur in growthy seasons when trace element levels in pasture are diluted, and less soil is ingested. Prevention by injection is generally cheaper than testing although liver biopsies from slaughtered animals could be worthwhile.

There are short acting injectables, e.g. Prolaject B12 which lasts six or seven weeks with 1-2ml required; or long-acting injectable, for example Smart Shot, which contains selenium and lasts six or seven months which requires 0.5ml at docking (lasting six or seven weeks) followed by 1ml at weaning lasting another eight months. Also, there are rumen capsules which last a year, and a 10g implanted pellet.

Cobalt sulphate can be applied with the fertiliser in spring (70g cobalt), although this can be unsatisfactory on soils where high manganese can interfere with cobalt uptake by plants. Pasture must be spelled for four weeks. Cobalt deficiency is common on greywacke and sandstone soils.

Iodine deficiency

This is rare, can be very seasonal and is often associated with pregnant ewes grazing brassicas. Iodine is an element of the thyroid hormones, which control metabolism, heat, and growth of various tissues such as the brain, and foetal development.

Clinical signs are an enlarged thyroid (goitre). There will be an increase in lamb mortality, especially in cold weather and lambs will be small and possibly hairless.

There are no reliable tests for iodine deficiency in the live animal.

The best test is to post-mortem new-born dead calves/lambs to determine the ratio of thyroid weight to body weight; any lamb with thyroid greater than 0.80g/kg is deficient in iodine.

In addition, general observation of the weight of the dam’s thyroid as compared to bodyweight of the newborn, to determine if the dam was iodine-deficient during her pregnancy, is useful.

Deficiency in ewes can be treated by iodine drenching from mid-pregnancy, or long-acting iodine injection (Flexodine) pre-mating.

Importance of selenium

Selenium protects cells and the immune system. About 30% of pastures contain insufficient selenium for livestock requirements. Clinical signs in sheep are poor lamb growth rates, white muscle disease in lambs, infertility in ewes (increased embryonic loss) and poor quality ram sperm. Selenium deficiency is more prevalent in growthy summers for sheep.

An increased risk of selenium deficiency can be alerted to by pasture analysis. Less than 0.03mg/kg DM suggest both sheep and cattle are at risk however this should be confirmed by blood or liver analysis.

For sheep, lambs should be sampled before weaning and ewes 4-5 weeks before mating. Serum concentrations less than 50nmol/l are deficient, greater than 100nmol/L are adequate. Liver selenium levels of less than 250nmol/l are deficient, and greater than 450nmol/l adequate.

For cattle, selenium deficiency reduces conception rate, calf survival and growth rates. Calves become stiff and unable to stand (white muscle disease) and will be affected from one to four months after birth. Monitoring should occur just before calving and at least three months after any selenium treatment has been done. Cattle are deficient when selenium concentration in the blood is less than 130nmol/l.

Warning – selenium toxicity is possible if treatments are administered incorrectly. You should confirm there really is a deficiency.

For cattle, selenium can be replaced with an oral drench, an injection, a pour-on, or added to the water supply through a dispenser. The drench and short-acting injection will give a rapid response and last six to eight weeks. Longer-acting supplements, lasting for 12 months, can be applied as injection or as a rumen bolus.

For sheep, a long-acting injection three or four weeks before mating will give protection until weaning. If the ewe is not treated, and their lamb deficient, the lamb can be treated at docking which gives 10 months protection.

If treatment is by drenching, the recommendation is four weeks pre-mating and again four weeks pre-lambing, then drench the lamb at docking. Lambs will require ongoing drenching at six to eight weeks.

Ewes can also be treated with a 10g pellet four weeks before mating. For both sheep and cattle selenium can be applied as prills to pasture with fertiliser, and care needs to be taken with both length of withholding periods (minimum four weeks) and the length of time the sheep get to graze on fertilised pasture (minimum eight weeks over mating, preferably 16 weeks).

Copper requirement

Sheep have a lower requirement for copper than beef cattle, which have a lower requirement than deer. Deer are poor absorbers of copper due to their browsing habit. Deficiencies are more prevalent in poor summers as clover contains high concentrations of copper and can also be low in fast-growing new pasture due to dilution.

Deficiencies in lambs can often correct themselves as the grass naturally restores high copper levels. Nevertheless copper can get very low in sheep and cattle. In the central North Island some farms have copper deficiency which make remedying a molybdenum deficiency challenging, as very excessive molybdenum levels cause copper deficiency.

Liming has also been implicated as increasing pH increases the availability of Mo in the soil. In my view (and others) there is a degree of paranoia among farmers with respect to molybdenum-induced copper deficiency.

Clinical signs of animal copper deficiency include “swayback” where the animal loses control of its movement, similar to ryegrass staggers, and there can be a high incidence of broken legs when handling lambs. Sub-clinical effects can include unexplained poor growth rates.

Low copper levels can be initially detected by clover herbage analysis in the spring. Animal tissue analysis (Optigrow) or liver biopsy (post-slaughter in sheep) would be more accurate – the liver has a large capacity for holding copper, so much can be held in reserve, buffering copper deficiencies while soil or animal deficiencies of molybdenum or copper are remedied. Deficiencies can be corrected with a short term injection (three month), which is not very reliable, or with copper bullets (5g for adult sheep). Deficiencies in ewes are best corrected mid pregnancy rather than treating lambs.

Copper deficiency in cattle is usually expressed as poor growth rates in heifers or poor conception rates in cows. There is a certain risk in administering excessive copper – I have seen dairy calves die within 10 minutes of a copper injection. So “little and often” is the advice. That is moderate levels of copper applied as: copper sulphate in stock water system if possible, orally (copper sulphate with or without worm drench), rumen bullets, injection, or copper sulphate in solution on feed supplements. Copper in the fertiliser is very expensive.

• Tom Ward is a South Canterbury farm consultant.

Note: NANOMOLE/LITRE: One nmol/l is an abbreviation for the words nanomole/litre. One nmol is one billionth (10 to the power of 9) of a mole, a mole being a measure which contains a large number of molecules or atoms (6 followed by 23 zeros).