Wikipedia
Fog fever is a slightly confusing name. Affected animals don't have a high temperature, and the term 'fog' in the name actually refers to a second lush growth of grass, not misty or damp environmental conditions. The scientific name is Acute Bovine Pulmonary Edema (ABPE). The condition occurs in hungry, typically adult cattle, having been fed on dried feed indoors, and then moved to foggage pasture (fast growing, lush pasture, with high protein levels). The cattle graze on the new feed, clinical signs begin within 1 to 14 days and death often follows within 2 to 4 days after that. The condition can affect up to 50% of the herd, and around 30% of affected cattle may die as a result. A similar condition has been reported on a wide variety of grasses, alfalfa, rape, kale, and turnip tops.