The cows are infected with malignant catarrhal fever, commonly called MCF.
From the chron.com
Perhaps she will have sprouted an extra arm and contracted bovine malignant catarrhal fever.
From the guardian.co.uk
Scientists have uncovered the mysterious life cycle of a virus that passes from sheep to bison and cattle, causing malignant catarrhal fever.
From the sciencedaily.com
State officials have confirmed that 19 cattle shown at the fair in September later died of malignant catarrhal fever, a disease caused by a herpes virus carried by sheep.