Agriculture, farming, animal husbandry, animal health, disease, Facial Eczema, prevention, zinc, zinc sulphate, administered in drinking water, zinc toxicity, copper and selenium.
By Dr Clive Dalton
Original 1991 information written by Dr Barry Smith and Dr Neale Towers, Ruakura Agricultural Research Station, Hamilton, New Zealand.
10. Facial Eczema: (Dairy cattle). Zinc sulphate. In drinking water.
Administering zinc sulphate via the drinking water is a very effective way of preventing FE in dairy cattle. There are four main methods of adding zinc sulphate to the drinking water of cattle.
- Using an in-line dispenser to add a concentrated solution of zinc sulphate into the water reticulation system.
- Adding zinc sulphate to a large tank (e.g. 22,000 litres, or 5,000 gals) which supplies the water reticulation system.
- Floating trough dispensers - large numbers of animals can be protected but there is less control of concentration than the other methods and the troughs may require twice-daily attendance.
- Direct addition to the water trough - this will only cope with very small numbers of animals.
- It is essential that zinc-medicated water is reticulated only to the livestock.
- Household water supplies and dairy shed water must be kept separate.
- Non-return valves may be necessary to avoid siphoning or back-flow problems, and water pressure and flow rates should be within the capacity of the diluting equipment being used.
- Except in the first day or two, cattle will not refuse zinc in drinking water at the recommended rates. However, they are will prefer un-medicated water to zinc treated water if given the choice.
- Make sure that livestock do not have access to alternative fresh water during the period that zinc is being added for FE control.
- Have supplies of ZINC SULPHATE and the equipment needed ready well before the FE season starts.
- Zinc dosing should begin as soon as the weather conditions (warm, humid, grass minimum temperature more than 13"C, heavy dew or 3-4 mm rain) favour spore growth and/or at the first signs that spore counts are beginning to rise.
- Don't wait until dangerous conditions arise, or until clinical cases are seen.
- Remember that the spore rises precede clinical symptoms by some 10-14 days, and to be effective zinc must be dosed before or at the time the animals graze toxic pasture.
- Farmers regularly monitoring spore counts early in the season could delay starting dosing until counts begin to rise (don't wait until they reach danger level). It usually takes more than a week for the earliest spore rise of a season to reach danger levels, so starting dosing immediately spore rises begin should provide adequate protection.
- On problem farms in particular begin dosing in mid-January and continue throughout the autumn.
- Stock should not be exposed to zinc unnecessarily and excessively prolonged zinc dosing lowers the safety margin.
- Cows should be introduced to increasing zinc concentrations in water over a period of about 3-5 days. Use one quarter the required dose on day 1, half on day 2, three quarters on day 4, etc. Increase the rate more quickly if spore counts are rising rapidly.
- Troughs on the reticulated system in paddocks that have not been grazed should be primed with zinc sulphate at the rate of 1 gram/litre (0.7 gram/litre monohydrate).
- Continue dosing through the expected FE season.
- Towards the end of the FE season dosing can stop when spore levels fall to low levels and weather conditions are dry and cool. But watch the weather and start dosing again if conditions favour spore growth again.
- If possible avoid dosing continuously for more than 100 days.
- After long-term zinc dosing ceases, protection will carry over for several days.
- Overdosing with zinc is toxic. Take care calculating dose rates and weighing or measuring the zinc sulphate.
- There is a 3-fold safety margin for dosing zinc over 60 days, i.e. if three times the recommended rate is given it will cause damage to the pancreas after about 60 days.
- The safety margin for dosing for longer periods is progressively reduced. Hence the need to use the correct dose rates, and avoiding unnecessary dosing for long periods.
- Pancreatic injury must be severe before effects on animal health are noted. The pancreas will recover when zinc dosing ceases.
- Direct addition of zinc sulphate to the trough or poorly designed dispensers can result in very high zinc concentrations in the water immediately after the zinc sulphate is added. This can give excessive intakes to animals drinking this water.
- Later drinking animals can be under-dosed and be left unprotected as incoming water progressively dilutes the zinc concentrations in the trough.
- Because elevations of zinc occur in liver and kidney (not meat) a withholding period of 1 week should be allowed before animals are slaughtered.
- When lactating and dry stock are watered from the same water source where zinc is added, the lactating cows will receive a higher daily intake of zinc because of their higher water requirements.
- On a weight basis, their consumption of grass and hence spores will also be higher.
- Long-term zinc dosing may interfere with copper and selenium metabolism, although it has not yet been shown to induce copper or selenium deficiency.
- In areas where these minerals are deficient supplement the animals with copper and selenium immediately after zinc administration ceases.
- Don't give copper supplements during the FE season unless clinical deficiencies exist. If copper supplements are required use an injectable preparation.
The most commonly used form of zinc sulphate is the heptahydrate; this is generally coarse greenish crystal. Also available is the monohydrate form; this is normally a white powder or fine crystal and is freer flowing. It is used at two-thirds the dose rate of the heptahydrate.
Ask the supplier if the zinc sulphate meets the Animal Remedies Board's specifications.
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.