A nice description of neat's-foot oil is at
http://www.militaryhorse.org/resources/ordreport/1940/ch1sec2.htm :

   " ... Neat's-foot oil, which has long been recognized as the best of
all oils for leather.  It is a pale yellow, fixed oil, made by boiling
the feet, less hoofs, and shin bones of "neat" cattle (cattle of the
ox type as distinguished from horses, sheep and goats).  It is the
preservative base of many saddle soaps and an ingredient of many oil
polishes.  Due to the fact that it is difficult and expensive to obtain
in its purest or "prime" state, many commercial products termed
"neat's-foot" are likely to have been "cut" with some mineral oil. ...
Always use 'pure neatsfoot'..."

An interesting short article about the craft of the leather tanner is
at http://www.motherbedford.com/Tanner.htm :

   "The tanner's craft was not a nice one; it was one of the smelliest
and physically hazardous occupations of our forefathers...  The tallow
and neat's-foot oil would penetrate the surface just enough to make it
pliable without reversing the tanning process."

Robbie Rhodes