In the past, primitive societies believed that evil spirits and divine wrath could cause an animal to lose weight, reports veterinarian and author Michael Thrusfield in "Veterinary Epidemiology." Now, scientists understand that viruses, bacteria and other microorganisms can infect cattle and cause serious diseases, which they can diagnose partly through the observation of weight loss. However, despite the advances of veterinary medicine and the use of vaccines, some diseases are still a threat to cattle breeders.
Johne's Disease
Also called paratuberculosis, Johne's Disease is caused by the bacteria Mycobacterium paratuberculosis. The infection is often difficult to diagnose at its early stages, according to Cattle Today. It causes intestinal inflammation that results in low milk production, diarrhea and, consequently, drastic weight loss. According to the British Department for Environment, Food and Rural Affairs-Defra, there is no cure for Johne's disease, thus farmers have to put down infected animals to avoid further contamination.
Enzootic Bovine Leukosis (EBL)
This disease is caused by a virus, which is responsible for the appearance of leukemia and multiple tumors. Progressive loss of weight, anemia, weakness and anorexia are among the symptoms, reports the British Department for Environment, Food and Rural Affairs-Defra. Skin lesions and tumor formation in various organs, such as intestines, liver and lymph nodes, can also happen. Farmers must slaughter all infected cattle.
Bovine Spongiform Encephalopathy (BSE)
Bovine Spongiform Encephalopathy, or BSE, is a new neurological disease that can affect animals older than 5 years. The symptoms include exaggerated reactions to touch or sound, weakness of the hind legs, skin tremors, excessive nose licking and loss of body condition, weight or milk production, according to the British Department for Environment, Food and Rural Affairs-Defra. The disease lasts for many weeks and it is fatal.