A parasite population can develop resistance to a chemical through:
Pour-on applications can be susceptible to under-dosing (see points above) plus caked mud, lesions, wet skin etc can reduce chemical uptake. Social licking may also decrease the actual dosage received.
Everyone working in the rural industry has a ‘duty of care’; a legal obligation to provide a safe workplace for everyone on the property.
The chemical is carried by the dipping fluid and deposited onto the skin binding on the hair of cattle as they are submerged and swim through the dip (Figure 1). Dip chemicals represent an on-contact kill but do not offer ongoing repellent for the same length of time as other chemicals do. Complete wetting of the animal gives complete skin/hair coverage with the chemical. Incomplete wetting leaves untreated areas where parasites can survive to re-establish the infestation when the chemical wears off.
Dipping infrastructure or facilities are usually permanent structures, frequently built on large cattle farms, official cattle tick clearing facilities and commercial facilities such as saleyards. They are generally unavailable on smaller farms due to the cost of the facility and maintenance of the chemical.
Dips are built to specifications that ensure full submersion of the animal including its head and ears.
A working understanding and experience in management of the dipping process is necessary for correct and safe application of chemical to animals.
Treatment for cattle tick (Rhipicephalus australis) is mandatory in preparation for movement of cattle into tick free areas. Western Australia, Northern Territory and Queensland have mandatory requirements to prevent the introduction of cattle tick from known tick infested areas to tick free areas. Certification of the dipping procedure for cattle movement across state borders or into tick free areas is required to be done in registered accredited premises with oversight by an inspector or accredited certifier.
In Queensland, movements of cattle into cattle tick free areas can also include on property clearance using an accredited certifier.
Some compounds used for dipping are subject to ‘stripping’. This is when the dipping chemical is removed or ‘stripped’ from the dip at a faster rate than dip wash, leaving a lower concentration of active compound to the volume of water.
Labels for products that strip include instructions for reinforcement (adjusting the dip concentration with the addition of a concentrated chemical) and replenishment (topping up the dip with more chemical at the starting concentration) to maintain adequate concentrations of chemical in the dip wash. It is important that these terms are understood and that the label directions are followed.
Detailed information on management of dipping is important to successful application of chemical via this method. See Management of a Plunge Cattle Dip.
Figure 1 Cattle dip. Image courtesy of Scott Bauer Wikimedia CC