This question arose on the Sarah Silverman Program on Comedy Central on a new episode on October 24, 2007, where Sarah and her sister sang, "Whatever happened to that white dog poop from the 70's? It went away as mysteriously as it came." People don't seem to give their dogs bones as much as they used to, and less bone meal is used in commercial dogfood (maybe because of mad cow disease). As a result, dogs eat less unnecessary calcium than they used to. Nowadays, people can also be fined for not picking up Fifi's crap on the streetcorner, so less of it lies about town. In a large yard where it doesn't get picked up, it spends longer time in the sun drying out and having useful organic material being eaten by copiaphages, leaving behind more inert materials...such as white calcium. If you remember, the white poops always did look shriveled and dried out.