I was reading the book The Chicken Health Handbook by Gail Damerow and while reading about breeding for resistance, it said that Leghorns and other light breeds are more resistant to pullorum than heavy breeds such as Rocks and Reds, but that Rhode Island Reds are more resistant to worms than Leghorns. I was just wondering what other breeds are more resistant/susceptible to certain diseases/parasites? I know that Sebrights are a breed that is more susceptible to Marek's than most others. Anyone know?