Your readers had probably, like me, never heard of "cocker up" before and told you what they imagined it might mean, based on the sound of the word Siehe Wörterbuch: cock
I can't find "cocker up" in any of my BE or AE dictionaries with a meaning "castrate". New Shorter OED has "Pamper, indulge, coddle. Also foll. by up." and "Rock unsteadily, totter", but nothing about castration. If you are sure that Australians use "to cocker up" to mean "to castrate" then please provide an Australian dictionary entry for it.
It is not a commonly used word in English, but the dictionaries do suggest that "aufpäppeln" is not far off. (That does not mean that it's suitable in your context, though. When you come across a completely new word, it's worth looking for it in a monolingual dictionary before you use it.)