Popular cow riddles are:
   
“What do you call a cow with no legs?”/“Ground beef.”
“What do you call a cow with one leg?”/“Steak.”
“What do you call a cow with two legs?”/“Your mom.”
“What do you call a cow with two/three legs?”/“Lean beef.”
“What do you call a cow with five legs?”/“Rare.”
   
“What do you call a cow with three legs?”/“Tri-tip” has been cited in print since at least 2007.
 
   
Wikipedia: Tri-tip
The tri-tip is a cut of beef from the bottom sirloin subprimal cut. It is a small triangular muscle, usually 1.5 to 2.5 lbs. (675 to 1,150g) per side of beef.
 
The scientific name of this muscle is m. tensor fasciae latae, inserted in the fascia lata, the connective tissue covering the m. quadriceps femoris, also called quadriceps extensor, a group of four muscles which in turn insert in the patella, or kneecap, of the animal.
 
Straight Dope Message Board
Do you know any jokes for 7-10 year olds? 
Tenebras
10-15-2007, 01:55 AM
Forgive me if these have been told before. . .
 
What do you call a cow with no legs?
Ground beef
 
What did the snail say when he rode on the turtle’s back?
(throw your arms in the air and yell) WHEEEE!
 
What do you call a cow with one leg?
Steak.
 
What do you call a cow with two legs?
Lean beef.
 
What do you call a cow with three legs?
Tri-tip.
 
Yahoo! Answers (February 10, 2008)
What do you call a cow with no legs?
Ground beef.
 
What do you call a cow with 3 legs?
Tri-tip.
     
Jonathan’s Blog
Dumb Jokes That Are Funny
Posted on June 14, 2008 by Jonathan McKee
(...)
COMMENTS
Matt Furby says:
June 14, 2008 at 1:57 pm
(...)
What do you call a cow with three legs?
-Tri Tip.
   
Twitter
Dis‏
@ItsDis
a joke: What do you call a cow with three legs?        Tri-tip.
12:19 AM - 21 Apr 2009
 
Twitter
angie‏
@babyvtec
JOTD 12.22.09 - Archie: What do you call a cow with three legs? A: Tri-tip. #fb
1:50 PM - 22 Dec 2009
 
Twitter
Marv‏
@docmarvy
@_boo What do you call a cow with three legs? Tri Tip.
10:34 AM - 26 Apr 2010
 
Facebook
Certified Angus Beef ® brand
June 20, 2012 ·
What do you call a cow without legs? Ground beef
What do you call a cow with one leg? Steak
What do you call a cow with two legs? Lean beef
What do you call a cow with three legs? Tri-tip
What do you call a cow with FIVE legs? Rare.
 
Special thanks to our new intern, Malorie, for today’s comedy routine!
 
Reddit—Jokes
What do you call a cow with three legs?
submitted May 30, 2013 by hitokirivader
Tri-tip.
What do you call a cow with two legs?
Lean beef.
What do you call a cow with one leg?
Steak.
What do you call a cow with no legs?
Ground beef.
 
Facebook
Drovers
April 15, 2016 ·
What do you call a cow with three legs? Tri-tip.
What do you call a cow with two legs? Lean beef.
What do you call a cow with one leg? A steak.
What do you call a cow with no legs? Ground Beef.
📷 @william_ladd
 
Reddit—TipOfMyTongue
What do you call a cow with 4 legs? (self.tipofmytongue)
submitted February 28, 2017 by georgecena1337
Alright so there are 4 parts to this joke:
What do you call a cow with 4 legs? (A cow)
What do you call a cow with 3 legs? (Tri-tip)
What do you call a cow with 2 legs? (This one has 2 answers: lean meat OR your mom)
What do you call a cow with 1 leg? (Steak/stake)
What do you call a cow with no legs? (Ground beef)
But I could have sworn that the cow with 4 legs had a better/second answer that wasn’t just “A cow” and it was way more funny.