Any age can develop diarrhea.
Johne’s disease is a disease of chronic diarrhea, weight loss, and poor production. It is acquired as calves but often does not cause illness until later in life. No effective treatment is available but numerous control procedures are available. Rumen acidosis is a common cause of diarrhea in transition cows but not commonly seen in calves less than 3-months old. However, it should be considered if there is evidence of a sudden change in the feed components or sudden access to a high carbohydrate source to which the calf is not conditioned. There are several different diseases that can cause diarrhea and fever in cows and calves. Salmonella bacteria is one of the worst causes of this disease in cows and calves. Salmonella bacteria can affect all ages of dairy cattle, including calves, and signs of Salmonella disease take on several forms. There are many different types of Salmonella that cause disease in cattle. Diarrhea in adult cattle can be caused by Johnes disease. There are relatively few other causes of diarrhea in adult dairy cattle: salmonellosis, BVD (bovine viral diarrhea), winter dysentery (corona virus) and a hot ration (excess carbohydrate in the feed) are the more common ones. Calf scours causes more financial losses to cow-calf producers than any other health problem in their herds. Calf scours is not a single disease; it is a clinical sign associated with several diseases characterized by diarrhea. Scours is the common name for diarrhea in calves. Diarrhea is a disease of the digestive system characterized by watery feces and increased frequency of bowel movements. The high water content in the feces results in water loss from the body (dehydration). While cattle of any age can develop diarrhea, most cases of calf scours occur under one month of age, with the majority occurring between roughly 3 and 16 days of life. There are a variety of causes of scours in baby calves.
http://www.northernlakesvet.com/pdfs/diarrhea-in-cows.pdf http://www.sciencedirect.com/science/article/pii/S0749072012000539 http://www.progressivedairy.com/topics/herd-health/0608-el-diarrhea-in-cows-and-calves http://www.johnes.org/general/_Diarrhea.html http://www.cattlenetwork.com/cattle-resources/baby-calf-health/Calf-Scours-Causes-prevention-and-treatment-121277154.html http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/20600/em8977-e.pdf http://veterinaryextension.colostate.edu/menu2/Cattle/Calf%20Scours%20101.pdf
what causes scours in dairy cows