The disease is caused by the ingestion of spores from the fungus Pithomyces chartarum, found on the pasture the stock graze. The fungal spores proliferate in warm, humid weather, typically from January to April or May depending on the season.
The spores contain the toxin sporidesmin, which, as a result of chemical reactions in the body, causes significant damage to the bile ducts in the liver.
The reaction causes the animal to be extremely photosensitive, resulting in the white areas of skin becoming so damaged from the sun they turn red and can peel off, leaving large, raw, exposed areas of tissue.
Signs of the disease might start with diarrhoea, a milk production drop, reddened and swollen white areas of skin, animals actively seeking shade, jaundice and death.
There is no specific treatment for facial eczema.
Good nursing, protection from the sun, zinc creams on skin, ad lib feed and water and supplementary minerals and vitamins all help recovery. Euthanasia might be necessary for severe cases where animal welfare is compromised or the prognosis is poor.
It is critical to understand the severity of a particular eczema season is not judged by the number of cows with peeling skin.
It has been estimated only 20% of clinically affected animals show outward signs of facial eczema such as red, peeling skin so there will be another four or five animals for every peeling case that don’t show any outward clinical signs yet have damaged and diseased livers.
There is a significant negative association between the amount of liver damage after a facial eczema challenge and cow survival – the greater the damage, the less likely the cow is to survive. That includes culling for poor performance as well as death from the acute disease and secondary diseases such as metabolic disorders.
Survival of young animals to the end of their second lactation in exposed herds is about 10% lower in heifers with moderate or severe liver damage than those with mild liver damage.
In general, young stock tend to recover better than older animals.
Zinc treatment is the cornerstone of eczema prevention.
However, the way we manage our zinc dosing can greatly affect the success of the protection.
The number one reason for failure is dose calculation errors. Check the instructions and weigh doses accurately. For zinc to protect the liver, the zinc has to be at 20umol/l in the bloodstream and the only way to reach that level is if the cows are dosed at full rates regardless of the spore count.
Half rates provide no protection at all as they cannot get enough zinc into the cow to hit 20umol/l. The only reason you should use half rates is to get the cows used to the taste in the water if trough treating. This half rate acclimatisation must be done well before the cows need any protection.
Weight assumptions for stock can be wrong. The weight range of individual cows in a herd might be as much as 200kg. That variation can result in some of the big cows not being protected.
With dose delivery trough treating is a very poor method of providing accurate dosing. It is so dependent on the amount of water consumed, which varies greatly between cows and different days for that matter.
Hot weather versus wet weather, individual cow taste, other water available in sources like creeks, hierarchy in a herd and evaporation from troughs are also factors.
Think about it, the accumulated evaporation from all the troughs on any given day will cause loss of zinc from the inline dispenser by directing zinc away from the trough the cows are using.
Individual drymatter intake must also be considered. Some cows eat more palm kernel so will drink more water. And cows drink more water if they have clean water available from clean troughs.
With in-feed dosing animal size affects consumption as does individual cow taste because some cows eat more so get more zinc.
The form of feed affects waste. Pelleted feed is more consistent than loose powder mixed into feed. Consider the ability of a feed wagon to thoroughly mix feed compared to a mixer wagon.
And different feed companies have different quality control levels. Most feed companies dose only to a cow of 450kg.
In-shed feeding has less variation in intakes versus in paddock or feed-pad feeding.
Drenching is generally a lot better at getting zinc levels high enough in the cow than in-feed and trough treating but farmers need to ensure the dose is correct and measure a dose from the gun.
Daily drenching is far superior. There is no evidence to prove every second or third day dosing keeps zinc levels up.
And if some cows are dried off earlier than the herd they do not go through the shed so they don’t get drenched.
Capsules give extremely consistent blood zinc levels but timing is critical. Don’t start too early and miss the critical period by running out too soon.
An important tool to check zinc dosing is adequate is to blood test for zinc and the liver enzymes that indicate liver damage. Check zinc levels early to give you time for corrections before it is too late.
To summarise, trough treating is not good enough to protect your herd from facial eczema. Trough treating with zinc is 5.5 times more likely to fail in protecting cows compared to drenching or using capsules. Always check dose and weight of the animals and be aware of the limitations of the different application systems.
It is important to know half dosing has no protective benefit, even during low spore count periods because you get protection only if serum zinc levels are above 20umol/l. That happens only at full dose rates.
Spraying pasture with fungicides can also be successful in preventing spore numbers reaching toxic levels. It is critical to monitor paddocks so the fungicides can be applied in time before levels get too high.
No prevention plan is 100% effective all the time but we are far more likely to control facial eczema in high risk areas with a combination of fungicide spraying and zinc dosing.
There can be so much variation between spore counts from different farms, paddocks and samples in a paddock that you should not solely rely on the spore counts printed for your area. Area counts at best show a trend from week to week but are very limited in their relevance to your farm.
You need to collect grass samples from your paddocks and take them to your vet for counting. You will get far better information about the risk facial eczema poses to your stock.
To take a grass sample select a paddock to measure. Use scissors to cut a handful of grass 1cm to 2cm above the ground. Repeat the process taking 10 paces between samples until you have enough to fill a bread bag. Avoid gates, troughs and areas sheltered by trees or hedges. Don’t collect grass roots or soil.
Collect sample in a clean plastic or paper bag and store in the fridge until you can get it to your vet clinic. Take samples each week so you can monitor the changes on your farm.
Aaron Chambers is farm services manager at Energy Vets Taranaki
