A test was done several years ago in one of the European countries, don't remember which one. These test, which I don't believe by the way, found that cow sinew was actually better than Deer sinew.  I do know that it is just as good as as Moose or Deer or Caribou sinew but as Steve says it is quite greasy.  When I have used it I washed it with dish soap and warm water before using it.  The leg tendons are what you want to use.  The big neck tendons are useless