It is important woolgrowers understand the regulatory limits of using chemical products on their sheep. Following the rules not only optimises the welfare of the sheep, it also maximises the safety of the operator, the health of the environment and the positive eco-credentials of Australian wool in the marketplace.
Wool growers rely on a range of animal health products to protect their sheep from internal and external parasites such as worms, lice and blowflies.
One consequence of using chemical products is the potential presence of residues in body tissues and wool for a period after the product’s application.
For all registered veterinary products in Australia, there are in place regulatory time periods after the chemical’s application that indicate when the residue that remains in, or on, meat and wool products will not exceed the maximum residue limit (MRL).
The Australian Pesticides and Veterinary Medicines Authority (APVMA) sets MRLs for all registered veterinary chemicals in agricultural produce.
To find out the time constraints, always read the product label or view the APVMA or ParaBoss websites.
The mandatory time constraints have been set to ensure lamb and sheep meat is safe to eat, wool and sheep are safe to handle, and wool scour effluent is safe for the environment.
SHEEP REHANDLING INTERVAL (SRI)
The SRI is the time between treatment and when wool or sheep can be safely handled without the need for protective clothing.
If an SRI is included on a product label, this must be observed to protect those handling the sheep or wool, and to protect the environment in the case of wool processing residues.
For some products, the SRI is short, only requiring the product to become dry on the sheep.
MEAT WITHHOLDING PERIOD (WHP)
The meat WHP is the time from chemical application to when an animal may be slaughtered for domestic consumption.
Although lice control and flystrike products are applied to the skin or wool of the sheep, the skin absorbs some of the product.
The specified WHPs are in place to ensure no detectable levels of these chemicals are left in muscle, fat or other body tissues.
The wool withholding period is equivalent to the wool harvest interval (WHI).
EXPORT SLAUGHTER INTERVAL (ESI)
In addition to the meat WHP, sheep producers need to be aware of the ESI.
The ESI is the time from chemical application to when an animal may be slaughtered for export.
Some products have a relatively long meat WHP or ESI.
Take care when treating lambs to ensure this will not delay their planned sale.
A trade advice statement (such as an ESI) might not appear on labels of older registered veterinary products, however all new products now include a trade advice statement.
If you cannot find the ESI on a product label, use the ParaBoss Products Search tool available on FlyBoss or LiceBoss.
WOOL HARVEST INTERVAL (WHI)
The WHI (equivalent to wool withholding period) is the time from application of a chemical to when the wool can be harvested (this includes crutching) to satisfy Australian environmental requirements.
Most chemicals used to treat external parasites, such as sheep lice and sheep blowflies, bind to the wool grease rather than the fibre itself.
The scouring process removes wool grease and most other contaminants at the same time, which can result in contaminated scour effluent and lanolin if the WHI is not adhered to.
You can estimate the pesticide residue levels on wool at shearing caused by lice or flystrike treatments by using the ParaBoss Wool Residue Tool
If a lice or fly treatment does not state a WHI or an SRI, then a default one-month period applies for mob treatments or for wound dressings.
Flystrike treatments for individual sheep have a default withholding period of at least one month for wool.
Find the SRI, WHP, ESI and WHI for registered parasite treatment products using the ParaBoss Products Search tool, available at
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