A parasite population can develop resistance to a chemical through:
Everyone working in the rural industry has a ‘duty of care’; a legal obligation to provide a safe workplace for everyone on the property.
Spraying for parasites can be conducted with handheld sprayers, desirably powered by a fuel or electric pump, or with the use of a spray race where cattle walk through a ‘tunnel’ of spray nozzles strategically mounted to give complete body wetting of treated animals.
Hand spraying and race spraying is generally relatively inexpensive and can be used for opportunistic treatments, when cattle are in yards for other husbandry purposes, or where only low numbers of cattle are to be treated.
Handheld sprays are a relatively cheap option, but formulations must be mixed carefully according to label instructions and applied thoroughly to achieve good effect. Cattle should be treated in a race rather than a holding yard to ensure correct application and make sure that all areas on the animal where lice may be present are thoroughly treated. As a guide, and depending on animal size and hair coat, between 4 and 10 litres of spray may be needed per animal for good effect. Ensure there is sufficient pressure to completely saturate the hair coat to skin level. Thorough application will be particularly critical for good effect on animals with a winter coat.
Figure 1. Spray race. Image courtesy of Queensland Department of Agriculture and Fisheries
Where available, and where a larger number of animals are to be treated, spray races may also be a suitable option for treating lice. When using spray races, it is important to ensure that each animal is calm and walks slowly enough through the race to get properly treated. Check periodically to ensure that all of the jets are working properly, and none have become blocked. Ensure there is sufficient pressure to completely saturate the hair coat to skin level. Thorough application will be particularly critical for good effect on animals with a winter coat. The chemical active in some products can ‘strip’ from the dip, meaning the concentration of chemical active in the returned wash may decrease as spraying proceeds, so pay particular attention to the label instructions to ensure that correct concentrations are used when the chemical sump is ‘topped up’.
Figure 2. The spray race completely coats the animal as it walks through the race. Image courtesy of Queensland Department of Agriculture and Fisheries