As we look forward to Summer, NIWA’s long term forecast predicts a Summer dominated by La Niña with above average temperatures and humidity across the whole of New Zealand. Whilst this might be good news for those lucky enough to go away on holiday this year, La Niña is predicted to bring more north-easterly winds causing more periods of warmth and humidity – a catalyst for the rapid increase in fungal growth and spore production.
When combined with summer feed shortages and increased grazing pressure, could lead to higher growth of the fungus that produces the ‘facial eczema toxin’, sporidesmin. There may also be wider mycotoxin challenges placing extra pressure on the liver.
Prevention, not cure, is the key to facial eczema control, as serious liver damage may be irreversible. The first effects are loss of production, compromised immune function, and some cows may die later when exposed to high levels of stress such as at calving. As a rule of thumb, 1% of animals show clinical signs of facial eczema, then about 10% are likely to be sub-clinically affected.
Spore count monitoring programmes can help identify when levels start to rise, but individual farm monitoring is preferable, as more relevant to farm conditions, bearing in mind that conditions vary across a farm. Zinc dosing is more effective when started 2-3 weeks before a sporidesmin challenge, so waiting until levels start to rise may not be the best option.
Zinc can be administered via a bolus, drenched (zinc oxide or sulphate) or through water dispensers (zinc monohydrate or heptahydrate sulphates). Typical dose rates for facial eczema prevention are 2g elemental zinc per 100 kg liveweight. Zinc sulphate is relatively unpalatable, so target intakes may not be achieved, particularly in wet weather, or where animals have access to alternative water supplies. Supplying a flavoured trace mineral fortified zinc product would be a more suitable option.
Don’t forget your copper levels
High levels of zinc reduce the availability of copper in the diet, often resulting in depletion of copper reserves in the liver over the treatment period. There are also concerns that inorganic copper (copper sulphate) may increase liver damage in cows suffering from FE.
Offering an organic copper, such as NutriPlex® Copper, that contains B-Traxim Copper from Pancosma, can reduce the risks associated with feeding copper sulphate and help to maintain adequate liver copper levels during extended periods of dosing with zinc to combat FE.
The following table highlights the different ways to help prevent facial eczema; in water, in feed and drenching zinc and trace minerals over the FE period.