Rotavirus, Coronavirus, and Calf Diarrhea on Dairy Farms

Rotavirus and Coronavirus have been found to regularly circulate in youngstock and adult cattle on all dairy farms that have been intensively tested. In adults, the infection is commonly not associated with disease. In calves, it is associated with a range of signs from normal to mild diarrhea, to severe diarrhea. The relative distribution within these categories seems to be determinded to a great extent by certain herd management practices. In some farms, rotavirus and coronoavirus are associated with mild or no clinical signs and in others the balance is shifted toward severe disease.

Note that it is not the presence of rotavirus or coronavirus on a farm that distinguishes these two extremes – most calves will be infected with these two viruses whatever the rate of severe diarrhea. These viruses (and certain other agents on dairy farms, such as cryptosporidium and other coccidian) are termed “hyper-endemic agents,” meaning they are always present in the population of a farm, and most individuals are eventually infected. The ultimate goal of diagnosing and solving farm health problems is to determine how the farm in question differs from those that are not having the problem. In this light there is no evident diagnostic hypothesis that can be tested with regard to rotavirus and coronavirus, and thus submission of samples for assays for these viruses seems difficult to justify. It is rather like testing for gravity as the cause of the barn collapsing or oxygen as the cause of the barn burning down. Certainly gravity and oxygen play integral roles in causality of these misfortunes, as do rotavirus and coronavirus in calf diarrhea problems. But tests for their presence (gravity, oxygen, rotavirus, coronavirus) lack the ability to add any new information.

From a utilitarian viewpoint, the “causes” of dairy calf diarrhea problems are factors that affect specific and non-specific resistance of calves (good passive transfer rate, energy status, and others) and those that affect exposure dose of pathogens (housing hygiene and ventilation, hygiene of feeding and treatment equipment and hands, and others).

The goal of the diagnostic effort should be to carefully examine these potential causes, and this must be done systematically. You cannot properly evaluate energy status of calves just by looking at them. Nor can you evaluate passive transfer by asking a few questions. Nor evaluate adequacy of housing and hygiene just by looking and sniffing. The reality seems to be that we can come a lot closer to solving dairy calf problems by focusing on detailed evaluation of key management areas than by testing for gravity or rotavirus.

Washington State Dairy Newsletter
December 2006
Dale Hancock DVM, PhD, Epidemiologist,
Field Disease Investigation Unit
Washington State University