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Monday, 31 October 2016

Facial Ezcema Management

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Facial eczema occurs when ruminants ingest spores with toxic sporidesmin from the Pithomyces Chartarum fungus. This fungus is always in pasture swards but only sporulates in warm, moist conditions - usually rain after a hot, dry spell.

The fungus lives at the base of the pasture and a lot of dead matter and litter in the base of the sward provides the perfect environment.

Clinical FE shows up as photosensitivity (like scald from rape) but most incidence of FE is sub-clinical damage to the liver. Liver damage affects all production. It is estimated that if 5% of your flock show clinical signs of FE, that 50% will be suffering from sub-clinical effects. This is the hard part of managing FE - sometimes you don't even realise you have a problem. Even sub-clinical effects can reduce lifetime productivity by 20%. This liver damage is irreparable and cumulative so a five-year -old ewe who may have had small amounts of exposure in several years might have a badly damaged liver - they do not get "sensitised" to it.

This sub-clinical liver damage shows up through poor scanning result in ewes, depressed growth rates in young sheep and cattle, and in severe cases, death. Ewes that are affected by FE when in lamb can use their lamb's liver to filter toxins but then when they give birth and don't have the on-board dialysis system, they die.

You can't cure FE. Once the liver damage is done it’s there for the life of the animal and the subsequent drop in production is locked in.

Be wary of companies pushing products that claim to undo the effects of FE.

You can treat affected animals by giving them shade, water, and a low- protein diet that doesn't include chlorophyll (hay, silage, hard feeds).

Facial eczema can have a big impact on farm production but there are several ways to manage it. These are broadly categorised into short term management techniques (season to season) and long term management techniques.

Short Term Management

Spore Counting
The first step to addressing a FE problem is to know you have a problem. The production effects of facial eczema will be harder felt in areas that were "virgin" FE areas because they weren't aware of the problem until it was too late.

Pasture samples can be submitted to have spore counts taken. Most vet clinics will do it (a sample costs around $40) or many clinics will post spore counts on their websites weekly.
Alternatively Assure Quality put out weekly monitoring reports for regions on their website.

Ravensdown offers both Faecal and Pasture Spore Counting services.

Counts of 80,000+ are usually considered dangerous but by this stage the horse has already bolted. When spore counts get to 20,000 and rising you want to start taking preventive action on farm. At this point it might be good to start testing samples from your farm rather than using published district averages.

Use of Alternative Forages
Crops like chicory, clovers, Lucerne, plantain, and brassicas are considered FE safe. If you have these crops incorporated into your cropping rotation, try to graze pastures through the early summer and have these crops coming online through the high- risk periods. These crops might be prioritised to the animals most at risk of an FE outbreak.

Grazing Management
Your grazing management can minimise the risk and impact of FE spores. If you can understand the triggers in pasture you can minimise the risk. The fungus needs warm, moist conditions and dead matter in the bottom of a sward is a great environment.

Avoid the build-up of dead matter - Get your stocking rate right in the late spring/early summer to avoid pasture "getting away on you". This will minimise the build-up of dead matter and limit the habitat for the fungus.

Know where the high and low risk areas are - If nor'west winds are predominant and drying then NW-facing slopes might be considered low risk as they won't get the moisture required for the spores to multiply. Conversely in some areas the colder southerly faces will be low risk as they won't get warm enough. These are rules of thumb and working out the high and low risk areas on your farm might take a bit of testing over years to get a good handle on.

Don't graze too low in the sward in high risk times - the spores live at the bottom of the pasture sward so in danger times don't push stock to clean up paddocks.

On a whole farm system you will need to think about how this will work.

  • Get your stocking rate right to avoid the build-up of dead matter at the base of pastures.
  • Graze at-risk paddocks harder before the high danger periods and leave a bit more pasture in the low risk areas to graze at the high danger periods.
  • Plan for crops or safe forages to be grazed by important classes of stock (ewe lambs/ewes) in high danger times. This can have other positive effects at tupping by also avoiding other endophytes that can have a negative impact on ovulation.

Zinc Treatments
Treating animals with zinc can negate the effects of FE as the zinc reacts with the sporidesmin and stops the damage to the liver. Zinc can be administered by an oral drench, a slow release zinc bolus, or in many dairy farm situations into drinking water.

You need to be quite proactive with zinc treatment to start before the spores are ingested but not so early that you develop zinc toxicity.

Oral drenches can be a bit impractical as for best protection animals need to be treated twice a week (or even daily). Drenching every fortnight will reduce damage by up to 50% but is still a big commitment in a large ewe flock.

Zinc boluses will cost around $3.30 per capsule and will give protection for 6 weeks (note, in some seasons the danger period can continue longer than 6 weeks).

Fungicide Spraying
There are fungicides available that can be applied to pasture. These sprays will interfere with the production of spores but won't kill the spores/fungus already in the pasture so you need to be proactive with application before the spore counts get too high. This treatment will significantly reduce the spores for up to six weeks but it isn't a 100% fix so keep testing pastures.

Long Term Management - Breeding FE Tolerant Sheep

Some sheep are more tolerant to FE than others and it is a very heritable trait (0.42). Some stud flocks will annually test the resilience of their rams to FE each year using the RamGuard test provided by AgResearch.

The test isn't cheap - it costs about $300 per ram so breeders won't test all their rams but should at least test their elite sires that they put over their stud ewes.

It's a bit of a brutal test - basically the rams are given (poisoned) with a specific dose of sporidesmin. If this causes liver damage, an enzyme is released by the damaged liver which can be picked up in a laboratory test. If no enzyme is present, the ram is resistant to that level of challenge.

Typically a stud will start off challenging at a lower dose and as the resistance of their flock builds up over time will increase the dose their rams are challenged at. This level of challenge will give the stud a RamGuard flock star rating with a dose less than 0.20mg/kg LWT giving a one-star rating and a dose greater than 0.60 a five star rating.

If a stud has been challenging at least 10% of their sale rams with a dose rate greater than 0.60 for more than 10 years they achieve an FE Gold status. There are only 18 in NZ - the list can be viewed on www.fegold.co.nz.

You can't just put an FE tolerant ram over your ewes once and hope to be safe. Only about 40% of a ram's tolerance will pass onto his progeny so it will take several generations to build up tolerance across your whole flock. Also a stud won't test every sale ram and not every ram they do test will pass. So while a breeder may be only putting tested rams over their ewes and making good genetic gain against FE, the specific rams you buy may not be tested and therefore some may not be tolerant. This will only work over your flock if you are consistent with it over several generations of your ewe flock.

Questions to ask a ram breeder:

  • How long have you being testing for FE?
  • What dose rate are you testing at?
  • Can I please see your RamGuard certificate? Important info is:
    • Number of years tested
    • Dose rate
    • Number of rams tested
  • Can I please see your genetic trend graph?

The last point is important not just for FE. The more traits a breeder selects for the slower the genetic gain will be. The risk is by selecting for FE tolerant rams that other important traits (fecundity, growth rates) will be slower. This is generally not an issues as the order of selection is to cull rams on the usual traits first, and then test the top ranked rams for FE tolerance not the other way around so for a ram to get to the point of testing it needs to have pretty sharp figures for the usual EBV's first.