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. Rumen acidosis, hypomagnesemia, and heavy metal toxicosis were included as secondary considerations. On the basis of physical examination and gross necropsy findings, results of clinicopathol ogic testing, and results of feed and water analyses, a diagnosis of hypomagnesemia was made. Control procedures that were implemented included changing the forage source and increasing the magnesium concentration in the diet.