Written by John Swire
Zinc content in forage is rarely deficient (less than one per cent of forages samples will have a deficiency) and the amount of zinc in forage compared to the amount available from a bolus is significantly greater (often 100 times greater).
As most animals will get above 90% of the zinc required from forage the amount supplied in forage is about 20 times the amount that an animal would get from a bolus. For these and other reasons there is no value in including zinc supplements in a bolus.
Whilst zinc is known to be critical for many enzyme factors, zinc deficiency is very rarely reported. According to Teagasc* “Zn deficiency can be induced by high feed Ca levels, which block Zn absorption from the gut. However 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 BVSC, PhD, MRCVS, Veterinary Director with Animax many elements interact and this can mean that copper that should be available in the diet of animals becomes bound or unavailable. So sometimes a zinc deficiency is really related to a copper deficiency.
It is important to monitor trace element levels in ruminants in all situations. Bear in mind that changes to pasture, such as reseeding or liming, may change the 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 25 mg/kg dry matter. Typically pasture levels vary between 20-60 mg/kg dry matter, but this depends on factors such as grass growth, season and soil type.
Some trace element bolus 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.
Animax are best known for their Tracesure range of leaching boluses which deliver a prolonged release of the key trace elements. Copper, cobalt, iodine and selenium are 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.
Sadly, one bolus manufacturing firm in particular is pushing zinc supplementation in their trace element bolus! Jim Adair, Animax GB Sales Manager says that “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”.
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