Joseph Glatthaar gave an excellent talk about the organization and supply of the Army of Northern Virginia here, and you can read deeper with his book 'General Lee's Army: From Victory to Collapse' https://www.youtube.com/watch?v=Zy3OWWWARvw Suffice to say, the Confederates were operating on the slimmest logistical margins imaginable throughout the war, and by the time of Lee's surrender, conditions were utterly miserable. The men's rations added up to mere 900-1200 calories per day, a quarter of the 4000 required to keep up muscle mass during combat operations, and their horses received a scant two pounds of feed per day, a tenth of the twenty pounds issued to horses by the Union. Their rations was horribly short of essential vitamins and minerals, which left soldiers unable to properly absorb what nutrition they did get. Soldiers were forced to eat green corn at different parts of the campaign, with dysentary being a common result. The army came streaming apart as men, too weak to keep up on the march during those last awful months, deserted, drifting back to their homes. There was no way the Army of Northern Virginia would be able to keep up after the fall of Richmond.