The dipping of sheep can be traced back to the days of shepherding and is recorded in Britain as far back as 1280 AD, when tar was rubbed into the fleeces of the sheep as a remedy for scab. During the 19th century, sheep owners began to include other substances such as grease and rancid butter with the tar. This procedure was known as "salving". Understandably, this method was very time consuming and was not a very efficient method to manage outbreaks of scab.
The focus on protecting sheep welfare has been a matter of national importance in New Zealand from less than a decade after the signing of the Treaty of Waitangi (1840), and has continued through to the present. Legislation was developed to ensure that external parasites were eliminated, but little consideration was given to the adequate management of the chemicals used, disposal of chemical waste, and protection of human health and the environment.
After the first commercial sheep flocks were introduced to New Zealand in the 1840s, the colonial government in 1849 passed the Scab Ordinance, which endeavoured to control the infectious disease called sheep scab. This ordinance imposed fines on owners with scab-infected sheep and gave inspectors the power to order the destruction of infected animals. Although this ordinance did not enforce compulsory dipping, sheep dipping was undertaken to control scab.
The Sheep Act 1878 was the first legislation that imposed an obligation on farmers to dip sheep. Under this Act, penalties were imposed on any sheep owner found to have scabby sheep, and the Act specified that dipping must involve plunging or immersing. The Act did not require farmers to dip their sheep regularly - farmers were merely required to dip animals whenever necessary to avoid having infected animals. The number of infected sheep fell quickly in the early 1880s, so that by 1894 New Zealand was declared scab-free. The focus of dipping then shifted to the control of lice, flies and keds.
The Stock Act 1908 required every sheep owner to dip their sheep every year between a specified period, and penalties were issued for sheep that had not been dipped. This Act also stated that if any sheep being offered for sale were infected with lice, the owner would be penalised.
The Animal Remedies Act 1967 imposed an obligation on sheep owners to either dip or dust their sheep at least once a year. This Act specified that dipping must involve plunging or immersing the sheep in the dip, and that the dipping should be carried out within a specified period after the sheep had been shorn. An amendment to the Animal Remedies Act in 1982 also required that all sheep be dipped in accordance with the directions provided on the label of the dip chemicals.
Today, sheep dipping is no longer an annual legal requirement, but sheep need to be regularly inspected and any early infestation treated promptly. Pour-ons are less stressful than plunge dips and saturation shower dips according to the Code of Recommendations and Minimum Standards for the Welfare of Sheep.
Heritage dip sites are an important part of New Zealand's history, and some classic examples may qualify for heritage status. The Department of Conservation has recently protected a dip site on Quailburn Station, a former large sheep leasehold run in the high country near Lindis Pass.