Green’s Dictionary of Slang

cowsh n.

[abbr. cowshit n. (2)]

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

[NZ]McGill Dict. of Kiwi Sl. 31/1: cowsh nonsense, short for ‘cowshit’.
[NZ]McGill Reed Dict. of N.Z. Sl. [as cit. 1988].