Green’s Dictionary of Slang

(Aus./N.Z.) nonsense, rubbish.

c.1943		S .J. Baker Aus. Vulgarisms [t/s] 8: cowsh: An occasional substitute for the figurative use of bullsh, of which it is formed in imitation.
1988		McGill Dict. of Kiwi Sl. 31/1: cowsh nonsense, short for ‘cowshit’.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].