In's and out's of zinc

In New Zealand (NZ) interest and research in zinc (Zn) has mainly been for the purposes of facial eczema (FE) control. 

However Zn is also an essential trace element required for a wide range of body functions, especially reproduction and sex organ development, and to ensure the integrity of the immune system. The body has no stores available to be mobilised, so continuous absorption through the gut is essential.  

Zn deficiency has not been confirmed in NZ (Grace, 2010) so nutritional supplementation is not considered vital in our conventional farming systems. There is some anecdotal evidence that oral zinc supplementation decreases lameness in dairy herds in NZ but there is no good scientific data to support this. What is known is that addition of zinc sulphate (one kilogram into ten litres water) to footbaths is extremely effective at controlling foot-rot, in fact as effective as formalin, with the advantage of being safer to the user and environment.

The levels of Zn required for protection from liver damage in FE are ten to fifteen times that required for normal nutritional needs. This needs to be provided prior to the assault by the fungal spores to be effective. While Zn can be toxic in excess, poisoning is unlikely to occur under normal circumstances. However, the use of Zn in FE protection substantially increases this risk. Signs of Zn toxicity include reduced feed intake, depressed live-weight gain and decreased feed efficiency.

High Zn intake can also impair copper (Cu) absorption and this is thought to occur in the gut. This means that injectable Cu supplementation remains effective unlike oral copper sulphate products. Ideally, a herd should be checked for Cu levels following autumn FE Zn supplementation. This is best achieved by liver biopsy of eight to ten randomly selected cows, or as a second best option, monitoring of cull cows at the freezing works post slaughter.

Talk to your vet for more information and/or call the clinic to make a booking to get your cows checked.