Many factors contribute to the health, thrive and fertility of sheep. One important factor to consider is the role that trace-element imbalances can play in the reproductive health of sheep.

The easiest way to determine trace element status is through blood sampling and forage sampling carried out in conjunction with your vet.

For ewes, blood sampling 6-8 weeks prior to tupping is ideal, to ensure that any deficiencies diagnosed could be tackled well in advance of rams being introduced.

Trace-element imbalances

Below are some of the key trace-element imbalances to be aware of in Ireland.


Copper is utilised in enzymes which are responsible for thrive and fertility. It is also utilised for production of healthy wool and hair as well as for white blood cell function. White blood cell function is vital to the immune system.

Furthermore, during gestation the ewe requires copper to develop the lamb’s nervous system. Without an adequate source of copper mid-pregnancy the lamb’s nervous system is not formed correctly and cannot be treated – this is known as swayback.

Copper should never be supplemented to sheep without first consulting a vet to establish that there is a need as some breeds of sheep, in particular Continental breeds, are sensitive to copper. Excess copper can result in copper toxicity which can prove fatal.

While copper deficiency can be caused by insufficient copper in the diet, this is actually relatively rare. It is far more likely that sheep are ingesting high levels of other elements which antagonise or deplete dietary copper, causing secondary copper deficiency or Thiomolybdate Toxicity. This is often an issue on farms where high levels of molybdenum, sulphur and iron are ingested.


Cobalt is required by the rumen microbes for the production of vitamin B12 which is important for energy utilisation and is critical for growth, particularly in lambs. The body has no capacity to store cobalt, therefore cobalt must be continuously supplied.

Pregnant sheep

Selenium is vital for muscle function and deficiency can result in white muscle disease. Selenium deficiency is also a cause of impaired fertility, impaired growth, poor hair and wool quality and reduced immunity. 


Like cobalt, iodine is a trace element that ruminants have no capacity to store and a continuous supply must therefore be available. Where the animal’s diet is unable to provide this, supplementation will be required.

Stock deficient in iodine may suffer from:

  • Poor growth and weight loss;
  • Weak/Stillborn offspring;
  • Reduced fertility;
  • Goitre (enlarged thyroid).

Furthermore, ewes will not be able to transfer sufficient amounts of the element to the unborn lamb. This can result in lambs being born weak or dead.


Zinc is another trace element which ruminants have little capacity to store and so, where a deficiency exists, a continuous source of zinc should be supplied. Zinc is required in sheep for fertility, including sexual maturity and the onset of oestrus.

It also plays an important role in immune function, udder health, skin health, hoof health and wound healing.


If your vet diagnoses a trace element deficiency and has advised you to supplement trace elements, you have a number of options including oral drenches, licks and blocks, injections, pasture dressing, water supplementation, in-feed supplementation and trace element boluses.

Different forms of supplementation offer different advantages and disadvantages. Where trace element deficiencies exist, it is advisable to choose a method of supplementation which delivers trace elements in a controlled and consistent way, at levels that are consistent with the animals’ daily requirements.

Soluble-glass trace-element boluses

Bimeda’s CoseIcure and ZincoIsel boluses are made of a unique soluble glass which dissolve at a controlled and constant rate over the course of several months, providing sheep with trace elements at levels consistent with daily requirements.

CoseIcure delivers ionic copper, ionic cobalt, selenium and iodine. ZincoIsel is a copper-free bolus which delivers ionic zinc, ionic cobalt, selenium and iodine.

Ruminants have little capacity to store cobalt, zinc or iodine and a continuous supply must therefore be available. Soluble glass boluses are an excellent option for delivering a continuous supply of these trace elements, where a deficiency has been diagnosed.

Farmer’s experience

Joanne Devaney (also known as ‘Joanne The Shearer’) suspected that trace element deficiencies could be contributing to health and fertility issues among her flock

“In December 2020 we carried out forage samples on the mountain commonage in Sligo where we keep our flock of Mayo Blackface ewes,” said Joanne.

“We discovered that there was a deficiency in both copper and cobalt in the grass and heather.”

“We decided to try out CoseIcure sheep boluses. When we gathered the ewes in for scanning in late February, we were extremely impressed with the strength and condition of our in-lamb ewes after enduring a tough winter. It meant we could put most of the ewes back out onto the mountain, right until lambing.

Joanne Devaney

“We were so pleased with the results that we used the CoseIcure boluses again the following year on more of our hill sheep, and we have continued using them ever since.’

To find your local stockist of the Bimeda CoseIcure and ZincoIsel boluses, call Bimeda General Manager Andrew Glynn on; 087 252 5110, or call Bimeda Ireland customer services on: 01 466 7941.

Or to find out more about the boluses online, click here.