Bighorn sheep in Montana have been suffering from pneumonia since 2009. The pneumonia outbreak is responsible for around 500 bighorn deaths in western Montana. This past spring wildlife managers surveyed the results from culling the sick bighorns from the herds. By culling the sick bighorns the lambs had a better chance of survival, as well as protecting other bighorns from getting infected. Mike Thompson of Montana Fish, Wildlife and Parks tells the Missoulian that in two herds where sick sheep were killed and removed the survival rate for lambs is about 30 percent. In herds where culling was not possible due to the terrain, the lambs were worse off. Thompson also believes that by culling they have been able to keep 3 other herds pneumonia free. From NBCMontana.com .