Getting your money's worth from your zinc treatment

By Rebecca Weal, Otorohanga

It is that time of year again when you will all be watching the spore counts closely. With rain on the forecast (fingers crossed!) and cattle grazing low on pasture, the risk for a spore proliferation and subsequent significant facial eczema damage is very real.

Most of you would have implemented zinc treatment plans by now in some form such as in-feed supplements, in-line dispensers, Face Guard boluses and drenching. Even when plans are implemented we still see many cases of facial eczema every year due to inadequate zinc dosage, even when spore counts are reasonably low. Some common gaps in the plan include:

  • Dosing cows to an average body weight when there is a big variation- especially in mixed breed herds.
  • In-line dispenser malfunction or water delivery malfunction. Not priming troughs.
  • Supplementary non-treated water sources. 
  • Dominant cows hogging feed with zinc treatment in, subordinate cows missing out.
  • Not mixing zinc through feed evenly
  • Miscalculation zinc offered and uptake, not taking form and wastage of food into account
  • Starting treatment too late or not carrying on long enough

Cows without clinical signs of facial eczema can still have significant liver damage. For every cow that has clinical signs of facial eczema – photosensitivity, irritation – there are 10 cows who are sub-clinically affected and will have a decreased milk production.

A long period of mild-moderate counts of 20,000-30,000 can be just as damaging to the liver as a single week of high 100,000+ counts.

Copper sulphate supplementation should be stopped during the facial eczema season as it has been shown to aid in the facial eczema spores mechanism of damaging the liver. Copper sulphate also binds with zinc markedly reducing its effectiveness. Copper stores should be reassessed via liver sampling after zinc supplementation has finished.

There has been a lot of studies showing that despite methods of zinc treatment being put in place there is significant variations in blood zinc levels. One study showed that over 50% of all cows tested still had a blood zinc level below recommended target. This study also showed that cows supplemented through in-line dispenser units were 5 times more likely to have a lower than required zinc level than those cows who were drenched.

We recommend taking a blood sample from 10 cows in the herd 2-3 weeks after starting zinc treatment to check blood zinc levels.  The cows should be a range of ages, weights and production levels to get a good overall herd average. As well as checking that levels are in the target zone, it will show if there is any risk of levels being too high and potentially toxic. A second round of blood testing should be done 6 weeks into the zinc treatment when there has been moderate spore challenge (20-30,000 for 2-3 weeks) to check the liver enzyme levels as an indicator of treatment effectiveness.

Other quirks about FE:

If you have any concerns about your FE prevention plan don’t hesitate to contact us. It may be beneficial to check your herds zinc levels so you know all your money and effort is going towards an effective treatment. 

Rebecca Weal, Otorohanga


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