What does the acronym "DUNN" refer to when selling cattle?

I would guess that it actually means Dun...similar to the colour of a horse...

I have sometimes heard Limo and Charolais Xs that are that light reddish-blond colour refered to as dun colored.

Haussman, Haussman-Dunn gag

a speculum for examining the mouth cavity of cattle and sheep. Two horizontal plates accommodate the upper and lower dental arcades (upper dental pad in cattle). They are carried on ratcheted scissor-type mechanisms supported up each side of the face by a poll strap. When levered open the plates stay open until the ratchet is released. Gives excellent access to the mouth but excludes incisor teeth.

Sorry this is not an answer to your question but I am just wondering, how do you get the sideways smiley in your name??? =D