For some reason my first thought (having skimmed the title and obviously not taking in all the details) was that it had remained in the cow until now and was going to suggest that making a hole and grabbing it like so

would have been quicker, but I now after properly processing the information, I realise it probably shat it out not long after consuming it and it was lost to the muck all this time, and that poor cow is long gone. In which case the metal detector seems like the right tool for the job lol