Treatment for animal eczema threatens NZ lakes

A popular treatment used to combat the devastating livestock disease facial eczema could result in sterile freshwater lakes, experts say.

Writing in the New Zealand Land and Food Annual, Nick Kim, a Massey University senior lecturer in chemistry and toxicology, and Waikato Regional Council soil scientist Matthew Taylor point out that 5000–8000 tonnes of zinc is now being applied to Waikato pasturelands each year as zinc treatments for facial eczema are released with animal waste.

In only three decades, the average concentration of zinc in Waikato soils has doubled, Kim says, going from 30 to 60 parts per million. On about 10 percent of central North Island pastures, soil zinc levels now exceed 100 parts per million.

“That’s the lowest international guideline where you’re trying to protect soil microbial health,” Kim says. “That’s already reasonably surprising; it’s a really rapid accumulation.”

Studies show 21 Waikato freshwater lakes have elevated levels of zinc in their sediments, and so do marine sediments bordering coastal farms. 

The pair say the problem with zinc accumulation in the environment is that it could reach levels that affect the soil microbes, invertebrates, and plants that form the basis of complex food webs. Zinc can also cause antibiotic resistance in soil bacteria.

They recommend other alternatives to traditional dosing of zinc, especially as the disease is predicted to worsen under climate change.

Caused by the mycotoxin sporidesmin in pastures, FE damages the liver of grazing animals including sheep, cattle, goats and deer. In dairy cattle, it results in a sharp drop in milk production, and causes photosensitivity, skin irritation, and sometimes death. It’s responsible for $200 million a year in lost dairy production.

It’s also on the rise; last year was a horror year, with spore counts in some areas quadrupling or reaching the highest levels ever seen. The North Island was hardest hit, but so were some parts of the South Island, including areas in the West Coast that hadn’t seen FE for years. Supplies of zinc, the convenient and cheap treatment which prevents the toxin from damaging the liver, ran out in some areas.

Our history has shown that we tend to wait for the crisis to hit. In this case it would be nice to be ahead of the game.

The toxin flourishes in warm, wet pastures, and with climate change predicted to bring warmer temperatures and more rainfall, seasons with high spore counts will likely increase.

Kim adds that not only is treating an animal with zinc after it’s become sick a “medieval” approach to animal welfare, but there’s also the hidden burden of excess zinc resulting in a copper and cobalt deficiency, which can mean animals get sick more often, become susceptible to infection, and require more doses of antibiotics.

Te Awamutu veterinarian and facial eczema researcher Emma Cuttance says zinc can no longer be the first line of defence when treating facial eczema.

She has received funding through DairyNZ and the Sustainable Farming Fund to investigate the disease, and believes the best way for farmers to mitigate its impact is by carefully watching and managing their spore counts, using fungicides, investigating alternative pastures, and breeding FE-tolerance into herds, as has been done successfully in sheep over the past 30 years.

“I think as the planet warms, FE is only going to get worse,” she says. “It was predicted [by Dr Margaret di Menna] almost 45 years ago that this would be an issue in more parts of the country, but even that original research never predicted it to be as bad as it is now. The problem’s not going to go away, and we do need to prepare ourselves for no zinc at some stage in the future.”

Waikato Regional Council has identified zinc as one of their regional policy issues, but Kim says continued soil monitoring is needed.

“It’s not critical yet, but it’s at the stage of characterising the risks in order to meet them head on before they become critical,” he says. “Our history has shown that we tend to wait for the crisis to hit. In this case it would be nice to be ahead of the game.”

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