Facial eczema provides massive challenges during the summer months for New Zealand dairy farmers. To help better manage the potential risks, there are a few key points to understand and look out for.
What to look for
- Pithomyces chartarum is a fungus that occurs naturally on ryegrass plants. Under specific environmental conditions, the fungus multiplies and produces spores that contain a potent mycotoxin called sporidesmin. Ingesting increased levels of sporidesmin causes damage to the bile ducts of a cow’s liver and also to the mammary gland.
One of the first clinical signs of facial eczema is a significant reduction in the milk production of individual cows.
- Pithomyces chartarum spores multiply with increasing temperatures, humidity and moisture. Trash or litter at the base of a pasture sward is a breeding ground for spores and where we see the highest concentrations. So don’t force cows to graze down hard when spore counts are increasing.
- Reducing pasture litter is the first step in reducing the risk of facial eczema. Pre-graze topping can help keep spore counts lower for longer into the summer months. But remember, start early i.e. in September not December.
- Utilising summer crops can also be a sensible strategy, as Pithomyces chartarum is specific to ryegrass plants. Offering grass silage that was made before the spore counts increased will also be helpful.
- Pasture spraying is another prevention tool. Check the label of fungicides before application as they often require spore counts to be under a certain level to ensure efficacy.
Balancing rations for increased immunity
- There’s an argument that liver health – influenced by recovery from ketosis, fatty liver and liver fluke - may impact a cow’s capacity to deal with the Pithomyces chartarum challenge. ‘Bug’ populations in the rumen may also be a frontline defense mechanism, however quantifying this would be very difficult.
Maintaining adequate dry matter intake (DMI), balanced rations - especially rumen buffers and minerals - and providing antioxidants all aid metabolic and immune function to help cows deal with health challenges.
Most folks are familiar with using zinc therapies to aid in preventing clinical facial eczema. While it isn’t a watertight prevention, it is the best preventive treatment that we have.
A recent trans-Tasman review panel concluded that feeding zinc oxide to deliver 20mg of elemental zinc per kg of liveweight is required to increase blood serum zinc levels adequately for protection against liver damage. (Remember most zinc oxide supplements provide 80% elemental zinc.)
For example, a 500kg liveweight cow should receive 500 x 20mg elemental zinc, which equals 10,000mg (or 10g).
If your zinc oxide is 80% elemental zinc, to provide 10g elemental zinc, she must consume 12.5g of zinc oxide (10 divided by 0.8).
- During low challenge periods, zinc sulphate in water can be helpful to hold off on beginning zinc oxide therapy and can provide adequate coverage. However, as the challenge increases, water therapy alone can leave cows vulnerable when daily drinking water intake fluctuates. Crisis dosing levels may also be required in extreme circumstances.
- Half rates of zinc oxide are of no benefit when spore counts are high. When the spore count is up, you must feed the full rate to be of any benefit. Zinc must be fed before spore counts are high, as it cannot undo the effects of liver damage. Feeding high levels of zinc oxide can be continued for longer than 90 days, however this should be done in consultation with a veterinary advisor, who can monitor blood levels to avoid issues of zinc toxicity.
- Zinc oxide therapy is administered accurately via pellet feeding. Feed rates for pellets should be a minimum of 2kg per cow daily to ensure palatability isn’t compromised and to avoid increasing competition in the feed bin that can cause intake variations between cows. Individual cows that may not eat meal can have zinc oxide boluses administered. Adding zinc oxide to mixer wagons can have limitations in ensuring accurate delivery and would be best premixed with other feed ingredients.
A word of caution with copper
- And beware, recent studies have shown that additional copper catalyses the reaction of Pithomyces chartarum at the liver, which can further compound liver damage. Be cautious if you feel you need to provide additional copper to deal with any potential shortfall created by feeding such high levels of zinc. Part of the reason why high doses of zinc are effective in preventing liver damage is the fact that it effectively binds copper to prevent it from reacting with Pithomyces chartarum.
If you’d like more information on your herd’s summer ration, or options for adding zinc, contact your local Dairy Nutrition Specialist