There is no one answer to the question. There is one common theme from battlefields through the ages, you could smell them for miles. You will rarely read a memoir of a combat soldier who does not mention that. It was said that after Gettysburg, the battlefield could be smelled twenty miles away, so some troops didn't get a quick burial. A lot of the handling of dead bodies depended on which side controlled the battlefield after the shooting stopped. I have seen photos of Americans bulldozing dead Japanese troops into pits like so much garbage. (which reflects how they felt about them) Russians in WWII buried troops, many times in mass graves, when they could, but a lot of them were left to decay where they fell. Americans did a good job of policing up their dead and giving them a formal burying. (we eventually controlled all of our battlefields) Germans on the Russian front, buried most of their dead, unless on retreat, but the Soviets would destroy the cemeteries when they took their land back. (Who could blame them?) If you don't control the battlefield after the battle ends, your dead are at the mercy of your enemy. I have heard it told that there are places on the steps around Stalingrad, where you could go and pick up bones today. I don't know, I have never been there. Armies tend to address the issue as soon as possible for not only health reasons, but also because it is hell on morale to see your friends and neighbors being eaten by wild pigs or stray dogs. It makes a soldier think, "Oh crap, this could happen to me!" Out of sight, out of mind works best, and the quicker the better.