NotesThe dipping stick was used to dip sheep in Cooper's Arsenic Dip on the Wanganderry property near Mittagong, NSW between 1921 and 1989.
By the 1920s, when the Wanganderry property was established, it was common practice in Australia to dip sheep into a solution containing arsenic and sulphur after shearing. The chemicals killed lice, scab, blowflies and ticks. On Wanganderry, sheep were directed down into a narrow concrete swimming race at ground level filled with dissolved Cooper's Arsenic Dip. As a sheep swam along the race, a worker standing above it placed the dipping stick on the back of the sheep's neck and pushed the animal under the surface twice. This ensured that the whole animal was covered with chemical solution. The length of the dipping stick ensured that the worker did not have to bend whilst working and was unlikely to be splashed with chemicals. After dipping, the sheep climbed up the slope at the end of the race.
The first arsenic-sulphur sheep dip was made in 1843 by William Cooper, a British veterinary surgeon in Berkhamsted, England. Arsenic was the main ingredient in sheep dips in Australia until 1946 when organochlorine dips were introduced. Arsenic-based dips were completely phased out by the 1980s but old sheep dip sites remain hazardous because of the contamination of surrounding soil with arsenic. Organochlorine chemicals included DDT, benzene hexachloride (BHC), chlordane, heptachlor, aldrin, dieldrin, methoxychlor and toxaphene. Direct applications of the organochlorine chemicals were prohibited in 1962 due to the residues that remained in the fat of treated animals.
Organophosphate and carbamate chemicals were introduced in 1958. These included diazinon, dioxathion, carbophenothion, coumaphos, ethion, chlorpyriphos and carbaryl. The use of diazinon to control lice in sheep, using plunge and shower dipping, was subsequently prohibited in Australia in 2007.
Synthetic pyrethroids were introduced in 1981. They include cypermethrin, cyhalothrin, deltamethrin, alphacypermethrin, and lambacyhalothrin. Heavy use of these chemicals has resulted in the emergence of lice populations resistant to synthetic pyrethroids. The lice do, however, remain sensitive to organophosphates. Other chemicals introduced since 1985 include Macrocyclic lactones and insect growth regulators.
Over the years, alternatives to dipping sheep have been developed: Some chemicals are jetted (applied using high-pressure jets of fluid as sheep move along a race), others are showered onto sheep and others are poured onto the back of the sheep in a narrow line along the back of the animal. When the pour-on chemicals were developed in the 1980s, many farmers abandoned the use of plunge and shower dips. The main pour-on chemicals are Clout® ( a synthetic pyrethroid) and Zapp® (an insect growth regulator).