No, and I'm not even sure that there is one. I was not a DO candidate this cycle. DO schools have a slightly different model, because they collect significant, non-refundable tuition deposits ($1,000-$2,500) soon after acceptance, and they are more than happy to have you forfeit those deposits and call people off WLs, right up until the start of school. OTOH, MD schools do not ask for a deposit of more than $100, which is fully refundable until 4/30. Many schools ask for no money at all upfront.
DO schools understand that they are going to lose people to MD schools as long as the MD schools are still calling people off WLs. Their business model relies on it, since they generate a lot of revenue from these forfeited 4-figure deposits. This is a reason DO schools interview and accept a lot of people early in the cycle who are clearly strong MD candidates, and then start interviewing for the WL, also relatively early in the cycle. They do it intentionally in order to grab those non-refundable deposits from people eager to buy a little insurance early in the cycle, knowing they are going to be going to the WL in April and May.
I just don't know how common it is to hold multiple DO As, due to the significant deposit money involved, or whether and how schools induce people to drop multiple DO As between the time those deposits are paid and the first tuition payment is due.