According to the current USDA data available in 2008, cull dairy cows accounted for just over 7 percent of all cattle slaughtered in the U.S., but were responsible for approximately 90 percent of carcasses in which drug residues were detected. Some of the more common reasons leading to having a carcass condemned for drug residues include: 1. Changing the dose or route for Procaine Penicillin G: The label dose for PPG is only 1 cc per 100 pounds, or about 15 cc total. When a cow is given higher doses or treated subcutaneously (under the skin), the slaughter withdrawal time can increase from the label four to 10 days up to several weeks.