May 12, 2009

Facial Eczema (FE). Farmer Information. Part 8. Zinc oxide. Prevention by pasture spraying.

Agriculture, farming, animal husbandry, animal health, disease, Facial Eczema, prevention, pasture spraying, zinc oxide.

By Dr Clive Dalton

Original 1991 information written by Dr Barry Smith and Dr Neale Towers, Ruakura Agricultural Research Station, Hamilton, New Zealand.

8. FACIAL ECZEMA: Zinc oxide. Prevention by pasture spraying.
  • Spraying zinc oxide onto pasture before it is grazed provides a method of dosing large numbers of animals with a relatively low labour input.
  •  The method requires an area of sprayable land with sufficient pasture to provide grazing for a 12 or 24 h period.
  • The method works best when the grazing area is small and t he pasture is moderately long so that the percentage utilisation of the pasture is high.
  • A high pasture utilisation is needed to ensure that most of the zinc oxide is actually eaten by the grazing animals.
  • Dry stock can be protected by spraying pasture either once or twice a week.  Milking cows are best protected by spraying pasture daily - but note that the need to restrict grazing to maximise zinc intakes will affect production.
  • Milking cows could be protected by grazing sprayed pasture at 3-4 day intervals, but should not be given weekly doses of zinc oxide as this is likely to interfere with calcium metabolism and cause milk fever.
  • The method is not suitable for calves, which require lax grazing for good liveweight gains.
  • The major advantage with zinc oxide spraying is that it can give immediate protection when conditions are dangerous. Spraying fungicides may be more convenient and not much more costly.
  • Spray or dust a restricted area sufficient for 12 or 24 hours hard grazing.
  • Graze animals at stocking rates ensuring maximum pasture utilisation. Confine animals to the sprayed area.
  • Choose application rates to match the dosing interval (daily, twice weekly, weekly) and the estimated pasture utilisation expected (see tables below).
  • Any spraying system (boom or rose) with a high return flow through the bypass valve is adequate for applying zinc oxide. The high return flow is required to keep the zinc oxide in suspension; with an inadequate flow there is a danger of the zinc oxide settling and blocking inlets etc.
  • Continue spraying the area until all mixture is applied. Use largest possible nozzles and spray flow rates.
  • If a high-pressure water supply (yard washing system) is available pour the dry zinc oxide into the spray tank (place a piece of timber over the pump inlet first to prevent blocking) and use the high pressure water jet to disperse the powder while filling the tank.
  •  Alternatively, mix 5 kg lots into a slurry by hand and add to partly filled spray tank. It is easiest if the dry powder is poured onto water in bucket and left to settle before stirring. Don't pour water onto the powder.
Amount of Zinc Oxide to Use
  • Dose rates should be adjusted to compensate for changes in pasture utilisation as this controls the proportion of the zinc oxide applied that is actually eaten.
  •  Most of the zinc oxide will be on the upper parts of the sward. Zinc oxide ingestion is about 20 percent higher than the pasture utilisation.
  • On shorter autumn pastures utilisation rates of about 30-35 percent can be expected.
  • Choose the dose rate that best matches your estimates of pasture utilisation and average liveweight for your herd from the table below.
  • Multiply the daily dose rates by the number of animals to be treated.
  • For a 160 cow F x J herd with average weight of 400 kg eating about a third of the grass' offered.
  •  Daily dose rate = 20 g.
  • Total zinc oxide required 20 x 160 = 3200 g = 3.2 kg
 (Note: Not recommended for calves).
  • Daily spraying should have minimal effect on pasture palatability although cattle may show some initial reluctance to graze.
  •  Milking cattle can be protected by grazing zinc-oxide-sprayed pasture at 2 to 4 day intervals, but the dose rates need to be increased to compensate for the less effective protection.
  • If dosing at 2-, 3- or 4-day intervals multiply the daily dose rates by 2.5, 4 or 5.5.
  •  Other classes of stock can be protected by grazing pastures sprayed with zinc oxide once a week. This is not recommended for milking cows.
  • Cattle and sheep grazing pastures sprayed once weekly, may show reluctance to graze the pasture. It may be necessary to confine them to the sprayed area for more than 24 hours - check final pasture utilisation and adjust spray rates to match.
  • The table below shows the amount of zinc oxide to use for other classes of stock and various levels of pasture use.
  • If the pasture utilisation rate is not known assume a 30% rate.

This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.

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