Found this at the Fell Pony Museum website:

Salving Sheep

Before the days of sheep dips, from the 16th century until the beginning of the 20th, it was a known practice in Cumbria to "salve" sheep with a mix of tar and rancid butter. This involved parting the fleece at regular intervals along the animal's side and smearing the mixture onto the skin with one finger. It was done from the middle of October to the middle of November and was supposed to kill off lice, keds, ticks and so on which would otherwise feed on the sheep's skin or suck blood from her. It was a long and smelly job and a man could only salve a dozen or so a day, so to deal with a big flock took weeks. His pay was 2 pence a day.

The recipe called for 16 lb of butter to 4 quarts of soft, "roany" tar which was an American import; this quantity salved between 35 and 40 sheep. It was expensive, costing 8d a sheep in 1868, whereas dipping, which came into use from around then, cost only 1½d. Kirkby Stephen farmers had their own recipe, using oil and tallow. Yet the habit seems to have died hard, even though salved wool sold less well than clean wool. Salved wool was still sold as late as 1890, when wool at Appleby was reported as selling at the following rates: "Half bred hogg, 8d to 9d; black-faced (salved) 4d to 4½d; black-faced (unsalved) 5d to 5½d per lb."

One of the first farmers to take to dipping his sheep was Mr Irving of Shap Abbey in 1850 who used "Biggs' Preparation" for his aged sheep and "McDougall's" for hoggs.

In 1905 due to an outbreak of sheep "scab", Government regulations began to compel farmers to dip sheep, and the ancient salve was completely replaced by the commercial soluble "dipping powders".