Caption: "Hereford twins produced at the Agricultural Research Service Range and Livestock Research Unit at Miles City, Montana. Photo by Jack Dykinga (1943--)."

They can only be told apart by their ear tags.

Credit/Permission: Agricultural Research Service, Jack Dykinga (1943--), before or circa 2007 (uploaded to Wikipedia by User:Angusmclellan, 2007) / Public domain.
Image link: Wikipedia: File:Hereford twins.jpg.
Local file: local link: cows_hereford_twins.html.
File: Art_c file: cows_hereford_twins.html.