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Equine

Facial Eczema

The fungus Pithomyces chartarum which causes facial eczema in stock is only a problem when producing high spore numbers. The fungus commonly occurs and thrives in locations of warm ground temperatures coinciding with high humidity and moisture. The degree of severity and regularity of facial eczema outbreaks depends on the weather, the location of the farm and on grazing management. The problem has become more widespread in recent years because higher stocking rates necessitate closer grazing of pastures. This causes the animals to ingest greater numbers of the toxic fungal spores, which are prolific on litter around the base of the pasture. Weather conditions have also been very conducive to extremely high levels of spores in the pasture.

 

What to look for

  • a drop in milk production
  • cows are restless, seeking shade and lick their udder
  • exposed unpigmented or thin skin reddens, thickens and peels

Not all animals affected with FE show physical signs (i.e. clinical FE) although liver damage (i.e. subclinical FE) has occurred. It is estimated that for every clinical case there will be 10 cows with subclinical FE.

Milk production of animals with subclinical FE can be depressed by up to 50%. Blood tests can be used to monitor the extent of subclinical FE.

Badly damaged liver tissue will not regenerate. Chronic wasting and/or death may occur at the time of damage or months later when the animal is under stress (e.g. calving).

        

 

Prevention

1) Pasture Management

  • Don't graze pasture too low down
  • Use spore counts to find safe paddocks. Send samples into your local vet clinic for analysis.
  • Alternative grazing e.g. young stock off farm, crops
  • Stop topping to reduce pasture litter
  • Pastures can also be sprayed with fungicide, which will reduce the spore count by 55-60%
  • On highly susceptible farms recent research suggests that changing pasture species may help. Ryegrass, white clover pasture appears to be more problematic than chicory, red clover pastures for example.

2) Use of Zinc

Ideally start Zinc treatment 2-3 weeks before the spore growth danger period for maximum protection. Many vets are advising farmers to start now. Zinc acts by forming a complex with sporedesmin and thus eliminating its ability to form by-products that are toxic to the liver. Therefore prophylactic use of Zinc treatments is quite effective at reducing the risk of FE damage. However no system is 100% effective.

There are 4 basic methods of applying zinc:

  • Drenching – which will reduce the number of affected animals by 80-90%.
  • Trough treatment - less effective at 70-80%.
  • Pasture dusting – least effective
  • Slow release boluses (eg. Time Capsule Bolus¨). The best protection available

Note: be on guard for milk fever in cows when starting your zinc treatment programme as zinc interferes with calcium metabolism. Also if your area is copper or selenium deficient you need to seek veterinary advice before administering zinc to your stock.

 

Drenching with Zinc Oxide

Long term drenching gives the best protection. As opposed to crisis dosing (treating previously non-treated animals with higher rates of Zinc during danger periods only)

Stabilisers (seaweed based "fertilisers" eg. Maxicrop, or commercial stabilisers eg. Co-Zinc) increase ease of mixing and drenching and allow the mixing of more concentrated drenches. Less volume of drench is then needed per dose.

1) Unstabilised drench:

Sprinkle 10kg zinc oxide powder into 25 litres (5.5 gallons) water, leave to wet, then stir until lump-free. This produces about 27 litres of drench.

Long term daily dosing = 7ml/100kg liveweight (2.6gm ZnO/100kgLW)

Crisis daily dosing = 10ml/100kg liveweight (4gm ZnO/100kgLW)

3 day to weekly intervals long term dosing (dry stock only)= 10ml/100kg liveweight x No. of days between drenches.

2) Stabilised drench:

Mix 2 litres of "stabiliser" with 10 litres (2.2 gallons) of water then sprinkle 10kg zinc oxide powder on the water, leave to settle then stir to a smooth creamy paste. This produces about 14 litres of drench.

Long term daily dosing = 3.6ml/100kg liveweight

Crisis daily dosing = 5ml/100kg liveweight

3 day to weekly intervals long term dosing (dry stock only)= 5ml/100kg liveweight x No. of days between drenches.

Remember: When long term daily dosing 1kg of zinc oxide will dose 100 cows (400kg liveweight) for 1 day.

 

Trough Treatment

There are 2 forms of Zinc Sulphate available for use in trough treatment; Zinc Sulphate heptahydrate (normally a coarse greenish crystal), and Zinc Sulphate monohydrate (normally a white powder or fine crystal). Monohydrate is the more concentrated form and is used at 2/3 the dose rate of heptahydrate.

1) Floating in-trough dispensers:

Calculate amount of Zinc Sulphate to be added to the trough daily (a dosage chart can be obtained from your veterinarian) eg. 100 Friesian cows x 36 grams/day = 3600 grams of heptahydrate/day

Refill the dispenser twice daily with half the daily amount (ie. 1800 grams or 1.8kg) at each visit to the trough.

2) In-line dispensers:

Calculate daily dispenser requirements for ALL stock on the farm and then set the dispenser to deliver that amount eg.

200 Jersey cows x 28 grams/day = 5600
50 Jersey heifers x 23 g/day = 850
53 Jersey calves x 10 g/day = 530
TOTAL = 6980 g = 7kg heptahydrate/day

Note: Direct addition of Zinc Sulphate to the water trough without using a dispenser is not recommended

Zinc is potentially a toxic element, and it is easy to calculate dose rates and volumes incorrectly for trough and drenching systems. We recommend that:

  1. you have us calculate the optimal zinc treatment plan for your farm, and
  2. you have us monitor GGT levels in your animals over the peak FE risk period to ensure that your zinc application is effective.

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