Tuesday, March 5, 2024

Knowing the signs of subclinical facial eczema

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Clinical facial eczema presents with physical signs, but subclinical FE does not.
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Taking a proactive stance on facial eczema management is the best defence against the condition. 

Every dairy farmer is aware of clinical facial eczema and the potential for harm, but there’s a general lack of awareness of the prevalence of subclinical facial eczema (FE), and the harm this does to herd and farm productivity. 

The disease is caused by a toxic fungus called pithomyces chartarum, which grows on the dead plant matter at the base of summer pastures. The fungus spores produce a toxin that damages the liver and bile ducts, which in turn causes toxins to build up in the body. 

While clinical FE presents with physical signs – skin reddening and/or peeling, drop in production, restlessness – subclinical FE does not. However, liver damage will be present. There is no cure for facial eczema and recovery is dependent on the level of liver damage.

A 1998 study estimated an average loss of $6180 per dairy farm due to just clinical cases of facial eczema. Taking into account that DairyNZ estimates subclinical FE cases to be as high as 10 times those of clinical FE cases within the herd, that cost quickly climbs. 

A 2019 study run by VetEnt showed FE can cost farmers 0.14-0.35kg milk solids per cow per day, with one farmer in the study losing $125,000 in milk production. 

Understanding the signs of subclinical facial eczema and the risk levels on the farm goes a long way to establishing a comprehensive FE prevention plan.

An effective facial eczema prevention programmes takes a multipronged approach, including zinc supplementation, along with safe feeding and grazing. 

While zinc supplementation is currently the main way of treating facial eczema, a 2014 study of 1200 cows across 105 North Island dairy farms found that 70% of cows weren’t getting enough zinc to provide protection. 

This was primarily due to underestimating liveweights, inaccurate dosing, or incorrect product usage.

There is no cure for facial eczema and recovery is dependent on the level of liver damage.

Zinc supplements work by disrupting the production of liver-damaging toxins and, to be successful, supplements must send zinc directly to the liver. This is best achieved when zinc supplements are in sulphate or oxide forms, and is one of the few situations where chelated forms may not be as effective.

Zinc can be supplied as part of a balanced formulation that can be dosed through drinking water, or as part of a mineral prill form that can be fed in the shed, blended into feeds, or layered into silage wagons or mixer wagons. 

Certain antifungal sprays can be valuable in pasture treatment. However, timing these spray applications around changing weather conditions can be tricky. Getting the spray timing wrong can be catastrophic as there will be no control of the spore development and toxins can be formed very quickly. 

Determining paddocks with high spore counts and avoiding these during high-risk periods helps in protecting your cattle against FE. In the same 2014 study, 98% of herd managers had access to regional spore count data, but only 33% measured spore counts on their own farms. Investing in pasture sampling with your local vet is the best way to determine spore counts on your farm.

There is no one way to completely guard against facial eczema, but investing in a robust prevention plan will go a long way to reducing your herd’s risk this summer.

This article first appeared in the December edition of our sister publication, Dairy Farmer.

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