Zinc is critical for many enzyme factors and while deficiency is rarely reported, Teagasc's reference manual for vets and advisors points out shortages can be induced by high feed Ca levels, which block Zn absorption from the gut.

However, while primary deficiency of Zn is rare in ruminants, there is a common enzyme – copper zinc superoxide dismutase which is important for many reactions in the body. This enzyme contains copper and copper deficiency is still commonly reported as well as toxicity.

According to Dr Elizabeth Berry, veterinary director with Animax, many elements interact and this can mean that the copper that should be available in the diet of animals can become bound or unavailable. So, sometimes a zinc deficiency is related to a copper deficiency.

Consequently, she said it is important to monitor trace element levels in ruminants in all situations to include changes to pasture, such as reseeding or liming, likely to affect availability of trace elements. The weather can also affect availability – in wet seasons, animals ingest more soil than in dry years, making cobalt more available, but copper less so.

However, there is little evidence to suggest a deficiency with pasture levels of 25mg/kg dry matter. Typically pasture levels vary between 20-60mg/kg dry matter, but this depends on factors such as grass growth, season and soil type.

Some trace element boluses do contain zinc but it is important to establish a need to give extra supplementation of zinc, and to check copper status due to the common enzyme. For some trace element bolus, the amount of zinc is negligible and is unlikely to have an effect compared to the back ground level of zinc.

Jim Adair, Animax GB sales manager says: “Farmers and animal health suppliers need to understand that adding zinc to a bolus usually gives an inadequate return. The essential trace elements are cobalt, selenium, iodine and if appropriate copper”.

Animax' Tracesure range of leaching boluses deliver a prolonged release of the key trace elements – copper, cobalt, iodine and selenium, the four trace elements which are essential for supplementation in low trace element diets in livestock. The boluses leach known and optimum levels of these elements for up to six months.