An AgResearch scientist who's been analysing the effectiveness of treatment for facial eczema in livestock, says breeding animals that can resist the disease is the best long-term option.
Facial eczema breaks out in the North Island and upper South Island every summer and autumn, as spore levels build up in pasture.
In severe cases, it can kill livestock and costs the farming sector millions of dollars per year in lost production and treatment.
The main way that farmers protect stock is by adding zinc sulphate to drinking water or administering it in drenches or capsules.
Dr Chris Morris of AgResearch says there are no cheap options and breeding resistance to facial eczema is the only long-term solution.
He says scientist shave made a lot of progress in that both for sheep and cattle.
Meanwhile, facial eczema spore counts are still high in some parts of the North island, particularly in Waikato, the Bay of Plenty and Northland.