Judas Steer

The “Judas steer” was the one who helped the cowboys lead the other animals to their destruction in the stockyards. The terms dates from the 1800s cattle drives.
 
 
Western Slang, Lingo & Phrases
Judus Steer - Part of the cowboy’s job during the drive was to identify the Judas steer. Once at the end of the trail, the Judas could simply lead the other cattle to slaughter with no hassle. If a particularly good Judas was found, he was spared the meat hook and used again.
   
Everything.com: Judas Steer
Why’d they leave that one cow? Ain’t it good for meat? I asked my grandfather.
That there’s a Judas, a Judas steer, he answered.

He explained that a Judas steer (or just “Judas”) is a special member of a herd. The herd usually has one cow or steer that is “trained” or calm enough to lead the rest of the cows into the slaughterhouse without help of human “encouragement.” I can imagine that if I were a cow, I wouldn’t go readily into a building reeking of death. However, if I saw a trusted member of my herd going in first, I might be more easily persuaded. After all of the herd had been led into the slaughterhouse, they would extract the Judas steer and return it to the farm for future use. It is most obviously named after Judas Iscariot, the apostle of Jesus Christ that betrayed the “Son of God” with a simple kiss, revealing Jesus’ identity to the awaiting Roman guards who would arrest him and later crucify him. These cows could easily see the inside of a slaughterhouse up to a dozen times before being killed themselves, unaware which trip in which they would lead their fellow cows to their death would be its last.
   
(Dictionary of American Regional English)
Judas goat n Similarly nouns Judas buffalo. ~ bull ~ ewe ~steer {In ref to Judas Iscariot, apostle who betrayed Jesus]
A goat (or other animal) used to lead sheep (or other animals) to slaughter; fig. of persons; one who leads others to their destruction; one who serves as a decoy or lure.
   
8 February 1891, Chicago Daily Tribune, “He Doesn’t Even Admire Our Crowning Glory—the Stock-Yards” (article by Rudyard Kipling), pg. 26:
In the center of that yard stood a red Texan steer with a headstall on his wicked head. No man controlled him. He was, so to speak, picking his teeth and whistling in an open byre of his own when the cattle arrived. As soon as the first one had fearfully quitted the viaduct this red devil put his hands in his pockets and slouched across the yard, no man guiding him. Then he lowed something to the effect that he was the regularly appointed guide of the establishment and would show them round. They were country folk, but they knew now to behave; and so followed Judas, some hundred strong, patiently and with a look of bland wonder in their faces. I saw this broad back jogging in advance of them, up, up a lime-washed incline where I was forbidden to follow. Then a door shut, and in a minute back came Judas with the air of a virtuous plow bullock and took up his place in his byre.     
 
5 February 1899, Sunday Herald (Syracuse, NY), pg. 31:
Usually a “leader” has been brought along just for an emergency. The “leader” is a Judas steer, long-nutured in the Central stockyards and practiced in the ways of ships and gangways and salt breezes. He is willing to direct his doomed fellows on the road to ruin, and he is led up the plank first. A trusting heifer starts to follow and stops halfway. A practiced cattle-puncher removes her hesitation by dexteriously twisting her tail.
   
24 March 1900, New York Times, pg. 2:
“JUDAS ISCARIOT”—BUTCHERED
Armour’s Veteran “Leading” Sheep
Pays the Penalty at Last.
 
CHICAGO, March 23.—After having led thousands of confiding sheep to their death, “Judas Iscariot,” as he is called in the yards of Armour & Co., has paid the penalty of his treachery and has been butchered. For eight years “Judas Iscariot” has been the “leading” sheep for the company.
 
Last week Judas rebelled. He refused to work, and his execution was decided upon. It is said by stockmen that a sudden attachment for a snow-white feminine sheep among the victims is responsible for his rebellion and ultimate death.
 
13 November 1955, New York Times, “West Side Ending Cattle Run Epoch” by Clarence Dean, pg. 121:
Armour had the problem of getting is livestock from the pens to the slaughter house in the next block. Led by a “Judas” steer—or, if sheep, two “Judas” goats—and herded by drovers, they passed through an alley to Fortieth Street, east for half a block, then into another alley on the south side of the street to the elevator doors of the slaughter house.
 
29 March 1964, Austin (TX) American-Statesman, pg. A7, col. 1:
Long before Bevo, the mascot of the University of Texas football team, became nationally known to television audiences, Texas had another famous Longhorn steer named “Phil Armour.”
 
In the 1870s, he had led a cattle drive up the Chisholm Trail and had won the respect—and affection—of the cowboys. When the herd finally arrived at the Armour Packing Co. plant in Chicago, the drovers refused to drive the old steer into slaughter.
 
Instead, they named him after the founder of the packing plant and turned him back to the stockyards. For several years, he was the “Judas” steer who led the herds from the pens to the slaughter house. When he died, Armour officials directed that Phil be buried in a plot overlooking the stock pens.