From The Collaborative International Dictionary of English v.0.48 :
Stirk \Stirk\, n. [AS. stric, from ste['o]r a steer. See Steer
a young ox.]
A young bullock or heifer. [Prov. Eng. & Scot.] --Sir W.
Scott.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
stirk
n 1: yearling heifer or bullock