Fog fever, also known as bovine respiratory disease (BRD) or atypical interstitial pneumonia, is a respiratory disorder that affects cattle, particularly those grazing on lush, early spring pastures. This condition is predominantly caused by the ingestion of toxic substances produced by fungi present in certain types of forages, especially those in the genus Hypomyces.
The symptoms of fog fever can range from mild to severe and typically appear within a few hours to several days after the animal's exposure to the toxic compounds. Affected cattle may exhibit respiratory distress, labored breathing, coughing, reduced appetite, weight loss, and fever. In severe cases, pneumonia, rapid breathing, and even death can occur.
The primary cause of fog fever is the production of secondary metabolites by the Hypomyces fungi, which aggressively grows on fresh-growing grasses, legumes, and other forages. These metabolites, collectively referred to as tryptophan derivatives, interfere with the normal metabolism of L-tryptophan, an essential amino acid. This disruption leads to the release of excessive amounts of serotonin, which results in lung tissue inflammation and subsequent pulmonary damage.
Prevention and control measures for fog fever involve avoiding sudden changes in diet, especially when introducing cattle to high-risk pastures. Gradual transition and acclimation to lush forages, especially during periods of rapid growth, can help minimize the risk. Additionally, various management strategies, such as rotating grazing areas or reseeding pastures with lower-risk forages, can also be employed to reduce the incidence of fog fever in cattle. Prompt veterinary intervention with appropriate medications and supportive care is crucial in treating affected animals to prevent further complications and promote a successful recovery.
