Hypomagnesemia among cows in a confinement-housed dairy herd.

Between January and March 2002, 55 cows in a 1,200-cow commercial dairy herd in south Florida died. Most of the cows that were found dead did not have any clinical signs of disease prior to death. Because of a history of a feed change, a bloom of blue-green algae in cow cooling ponds, and initial necropsy findings of moderate enteritis, the preliminary differential diagnosis included clostridial enteritis, blue-green algae toxicosis, and mycotoxicosis.