The information and data taken from Cuttance et al 2016 and Dairy NZ

In a recent study, it was found that there are numerous ways to incorrectly dose with Zinc for FE. The following is a summary of these findings.

Incorrect dosing:

This is a very common area for errors such as:
• Miscalculation
• Incorrect live weight estimation
• Not knowing the dose rate
• Not measuring Zinc accurately
62% of farms that were able to estimate their daily dose rate of Zinc were giving less Zinc than required.
Under dosing will afford inadequate or no protection, in the face of high FE challenge.

Issues with specific supplementation methods:

Drenching:

• 22% of farms that relied on drenching do not drench on weekends. This is acceptable if compensatory doses are given, but overdosing can then be an issue.
• Check the accuracy of drenching guns frequently.
• Under dosing/ live weight miscalculations.
• Can be easy to overdose – be careful.

In Water (In-line, PETA dispensers):

• Least accurate method; cows supplemented using Zinc in water had five times the chance of having inadequate blood Zinc concentrations.
• Water intake is affected by weather, the stage of lactation, the dry-matter content of feed, taste and cow hierarchy – even if everything else is done to recommendations.
• In 25% of farms that relied on water treatments, cows had access to untreated water.
• Leaks or evaporation from other troughs may also reduce concentrations of Zinc in water
• 40% of farmers do not prime their troughs; priming a trough means that all of the untreated water that was already in the trough system is replaced by Zinc treated water, in time for the FE threat. If the trough is not primed, FE protection will not begin until the supplemented water has completely replaced the water that was already in the trough when supplementation began. Thus, depending on the grazing rotation, cows could go for a month before receiving a protective dose of ZnSO4. Trough priming needs to be done manually by adding Zinc to each trough, or by starting Zinc dosing at least a month before the challenge.

Mixed with feed

• There is a general confusion about dose rates.
• Meal with premixed ZnO -most farmers assumed the feed company had calculated the correct amount of Zinc required for an average animal and did not know how much was actually added to the meal.
• Variable feed intake between cows.
• ZnO needs to be very thoroughly mixed or else there is a risk of under or overdosing.
• Zinc can stick to the sides of silos.
• Need to allow for wastage when calculating dose (e.g. 5%).

Pasture Spraying

• There is a general lack knowledge of how fungicides work.
• Fungicides are only effective if applied before spores rise above 20,000.
• Fungicides must be applied to green growing grass – fungicides need to be absorbed systematically into the plant to be effective. This does not occur when grass growth has markedly slowed or stopped, as is common in many parts of the upper North Island during the summer.
• Fungicide application across the whole area where cattle will graze is essential; in particular, fungicide needs to be sprayed under trees and alongside hedges, areas where helicopter application will not reach.

Zinc Boluses

Zinc blousing is generally a reliable method.
Most problems encountered are due to:
• Under dosing (inaccurate liveweight estimation)
• Too long an interval between first and second bolus
• Bolusing too late (after liver damage has already occurred)

References
Cuttance et al 2016, “Facial eczema management protocols used on dairy farms in the North Island of New Zealand and associated concentrations of zinc in serum”, New Zealand Veterinary Journal, vol 66, no 4, pp 343–350.
DairyNZ 2014, “Facial Eczema – Management for New Zealand dairy herds”