"Guest: guest" got it right (06 May 13 - 11:44 PM, above) the process was called 'salving' or 'smearing' and was done to protect certain breeds from skin disease and other ill effects of winter pasturing & diet.

Exactly which pine tar from where got used in what recipe depended much on the politics and trade agreements of the year in question. eg: "Stockholm Tar" was the Swedish crown monopoly of "NorrlSndska TjSrkompaniet" (loosely: "The Wood Tar Company of North Sweden.")

Source: Tar Heel genes.
See also: The Rural Cyclopedia, Vol.4, Q-Z, Rev John M. Wilson, ed., (Edinburgh: A. Fullerton and Co., 1849, pp.135-138)