The umbilical cord is usually a smallish black/red stump on the chicks lower belly area. If you look a bit further up towards it's back you will see the vent and that is where you should look for signs of pasty butt. It is usually pretty easy to spot. Look for poop stuck to this area, especially in the fluff around the vent. A dab of olive oil or vaseline on the area will help prevent it as will a few drops of ACV (apple cider vinegar) in the chicks' drink water. See if you can find unfiltered ACV with the "mother". It has more health benefits than the filtered one, though both are good. I've been using filtered ACV with my chicks as it's all I could find and I haven't had pasty butt issues in a long time.
