How cobalt deficiency tests led to higher lamb weights

A split trial on a Dorset farm highlighted a 3.52kg uplift in weight gain and reduced susceptibility to worms in lambs supplemented for cobalt deficiency.

The result of the trial, at Dineley Farming, Shaftesbury, made the decision to supplement all lambs an easy one.

See also: How to work out flock’s trace element requirements

Farm facts: Dineley Farming, Shaftesbury, Dorset

  • 728ha farmed
  • Stonehill Romney flock of 3,000 outdoor lambing ewes, lambing mid-April
  • 1,500 stud ewes in “A Flock”, single sired, producing breeding rams for retention and sale
  • 1,500 ewe “B Flock” mob-mated to a Romney. Will switch to a terminal Suffolk, once ewe numbers have increased.
  • Hope to finish 50% from the “B Flock” this year
  • 1,000 ewe lambs
  • 223ha arable replaced with herbal leys, red clover leys or kale and rape
  • 30 Belted Galloway suckler cows and 60 stores

Cobalt is involved in metabolic pathways and energy usage in sheep.

The animal does not use the cobalt directly, but converts it to vitamin B12, which is the usable form.

Signs of deficiency include ill thrift, open fleeces and increased susceptibility to worms.

Trace element status was brought into question at Dineley Farming – which is run by Perin and Sonja Dineley – in 2019, following discussions with sheep vet Emily Gascoigne of Synergy Farm Health.

At the time, head shepherd Martyn Fletcher was concerned that lamb performance was consistently poorer on some outlying fields.

Nutrition and worm burdens were under control, with the farm adopting a strict worming strategy based on faecal egg counts. Consequently, trace element status came under suspicion.

Tests for cobalt deficiency

Rather than wait until the lambs were born in April, forages were tested to establish if deficiency was an issue.

Samples were taken from fields where performance had been suboptimal, and on pasture grazed by pre-weaned lambs.

Several tested low for cobalt. The ideal level of cobalt in autumn/winter grass (when levels peak) is 0.08mg/kg dry matter or above.

Emily says: “The low level in grass was an early warning sign that we were potentially in a low-cobalt, high-risk year.”

Ewes had traditionally been given a bolus containing cobalt, selenium and iodine four to six weeks before tupping.

However, these levels would have depleted by lambing.

The lamb will get some vitamin B12 from ewe milk, but by the time they are at grass, they will be more reliant on cobalt from grazing.

Emily advised blood testing eight average, healthy lambs, aged four to six weeks old, from one management group to see if deficiency was a significant problem.

This cost £150. Testing lambs at this age is essential to allow issues to be addressed before growth rates are hit, she says.

(See “Tips for avoiding cobalt deficiency in lambs”.)


Three out of eight lambs were low in vitamin B12, but selenium levels were sufficient.

As results were inconclusive, Martyn adopted a split trial involving 300, eight-week-old, twin-born lambs.

Alternate lambs were weighed and given 1ml of injectable vitamin B12.

Treatments were recorded on an electronic identification (EID) recorder.

Lambs that did not receive a treatment (the control) were sprayed for quick visual recognition.

When they were weighed 10 weeks later, lambs that had been supplemented were an average 3.52kg heavier than those that had not had the injection, equating to a 50g/day difference.

Martyn says a lot of the untreated lambs had also lost weight and had much higher worm burdens.

He says it was a no-brainer to supplement everything.

“We spent 89p [a lamb] and gained 3.5kg of weight,” he says. “Since that year, we now do everything with 1ml at six weeks of age.”

Much of the farm has since been planted with herbal leys, which are reported to be more efficient at drawing up trace elements from the soil. The plan is to re-run testing to see if supplementation is still needed.

Tips for avoiding cobalt deficiency in lambs

Vet Emily Gascoigne from Synergy Farm Health provides her tips for avoiding cobalt deficiency in lambs.

1. Challenge your mineral and trace element policy

Is an evidence-based trace element strategy followed, or is the approach simply the one that has always been used?

  • If trace element status has not been measured recently, work with the farm vet to investigate and blood-test lambs
  • The vet can also review all sources of trace elements (for example, mineral licks, concentrates, boluses, drenches) to establish if requirements are being met
  • Even if ewes have been administered boluses, this does not mean lambs are covered

2. Be aware that cobalt levels will vary from season to season and field to field

  • Soil type, type of forage grown and season all affect forage cobalt levels
  • Waterlogged soils are likely to be higher in cobalt than free-draining ones, which are more prone to deficiency
  • Levels tend to be higher in spring and autumn and lower in summer
  • Plant varieties vary in their levels of cobalt, for example, white clover typically analyses at 0.24mg cobalt/kg dry matter (DM), while timothy contains 0.09mg cobalt/kg DM
  • Liming can also reduce cobalt uptake into the plant

3. Investigate early rather than waiting until weaning

Blood testing is the most accurate way of establishing trace element status.

Blood-test lambs for cobalt deficiency at four to six weeks of age to ensure any deficiencies can be addressed before growth rates are hit.

Avoid waiting until weaning as it will then be impossible to salvage any dips in performance:

  • If growth rate is stunted before the lamb reaches 30% of the ewe’s body weight (for example, if a ewe weighs 75kg, and lamb growth rate is stunted before the lamb hits 22.5kg (30% of 75kg), it will be hard to recover that lost weight.

4. Consider an on-farm split trial

  • Supplementation should always be evidence based
  • If blood test results are unclear, adopt a split trial so half of the lambs are given cobalt and half are not. Weigh at the start and end to see if growth rates are positively affected. Supplementation can then be adopted if necessary.

5. Think about how lambs are supplemented.

There are various ways to supplement, either by supplying cobalt, which will be converted to vitamin B12 by the animal, or as vitamin B12 itself.

There is no right or wrong and the decision will be influenced by cost and farm system.

  • An oral cobalt drench is cheap and can be given to small lambs, but only lasts for one to two weeks, so lambs will need to be handled and drenched repeatedly. This might be appropriate in small flocks but is not practical on larger units.
  • Boluses have a long persistency of up to six months, but cannot be given to small lambs, making them impractical if lambs are below 10-15kg
  • Long-acting injectable vitamin B12 – products range in persistency from one month to six months’ activity. Ease of use should be considered when choosing a product.