Pen riders move through the feedlot corrals on horseback, watching the cattle with a sharp eye. They are looking for illness, weaving through the herd day after day. They hear the animal with atypical interstitial pneumonia (AIP) before they see it. There’s a rattle in the heifer’s breathing and loud grunting. When they locate the animal the rest of the symptoms become unfortunately apparent: shallow breathing with minimal coughing, slightly gaunt and standing away from the rest of the cattle. Sometimes the infected cattle will stand with their feet spread apart, their necks extended and their heads lowered. Cattle with a serious case will be open-mouth breathing, often dripping froth and saliva. Green stool can be seen throughout the pen.

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