http://en.wikipedia.org/wiki/Frankfurters#Ingr edients
Ingredients
There is no fixed specification for hot dog meat, with pork and beef being the most popular. Less expensive hot dogs typically contain chicken, due to the low cost and availability of mechanically separated chicken, and some pork. Hot dogs are generally regarded as unhealthy insofar as most have high sodium, fat and nitrate content. Contents can also be questionable, with cheaper types of hot dogs having been known to contain snouts, ears, and blended organs. In recent years, due to changing dietary preferences in the U.S., manufacturers have turned to turkey, chicken, or vegetarian meat substitutes as well as lowering the salt content.
In general, if a manufacturer produces two different hot-dog-type sausages, "wieners" tend to contain pork, and to be the blander of the two, while "franks" tend to be all-beef, and more strongly seasoned. This is particularly true of Oscar Mayer.