Over recent weeks there have been reports of diarrhoea in more than 20 housed dairy herds in England, Wales and Scotland. The pattern of acute onset diarrhoea, with variably severe milk drop, is suggestive of ‘winter dysentery’, however other possible causes, including, in particular, nutritional factors, should also be considered.

Winter dysentery
Winter dysentery is a highly contagious disease that is caused by bovine coronavirus infection. It most commonly occurs early in the housed period, usually affecting adult cattle, but with up to 100% of the herd (including youngstock) sometimes developing signs. Most have watery diarrhoea, but in some herds, as the name suggests, there is a more dramatic presentation with bloody diarrhoea or dysentery. Affected animals are rarely pyrexic, although there may be malaise, loss of condition and reduced appetite. The disease outbreak spreads rapidly, and clinical signs in individuals usually resolve spontaneously in two to three days. A significant reduction in milk yield is commonly reported. Mild respiratory disease, such as coughing, might also occur. Mortality is uncommon.

Recent cases
On the affected farms up to 50% of the adult herd has been affected, with around 4 to 7 litres reduced milk production per cow. Most have recovered after a few days without treatment, although some cows have become very sick and been treated with oral fluids and non-steroidal anti-inflammatories. In two of the herds, group C Salmonellae have been isolated from affected animals, however the pattern of the disease outbreak spreading through the herd, and the associated clinical signs, are not considered typical of salmonella infection as the primary cause.

Testing for infectious diseases
Coronavirus is shed in faeces, however, due to the dilution factor in adult cows, and probably also because virus shedding largely precedes clinical signs, antigen ELISAs to detect the causative virus in faeces are often negative. Antibodies to coronavirus are common in cattle, so single sample serology is unhelpful, whereas paired serology can detect rising antibody titres in blood samples collected three to four weeks apart. Sampling at least five or six animals is recommended.

Other infectious causes of a herd diarrhoea outbreak which should also be considered include bovine viral diarrhoea (BVD) and Schmallenbergvirus (SBV) infection (although SBV infection would be unexpected at this time of the year as it is spread by insect vectors). Testing acute blood samples by polymerase chain reaction (PCR) can be done for both of these infections, or paired serology can be undertaken. Infection by Salmonellae is also possible and bacteriology on faeces samples is recommended.

Non-infectious causes
Feed-related causes are also to be considered and investigated, for example sudden changes of constituents, spoilage such as caused by moulds, and too high inclusion rates of concentrates, which risks acidosis. Potential management and nutritional factors should be investigated.

Surveillance
Please contact the APHA Veterinary Investigation Centres to discuss cases. It is important that they are aware of the occurrence of such outbreaks, and can advise on-farm investigations. Although there are several recognised causes of herd outbreaks of diarrhoea, as previously outlined, we must remain vigilant to the possibility of novel diseases; it was the increased numbers of reports of herds with diarrhoea, accompanied variably by milk drop and pyrexia, that enabled the Dutch Veterinary Surveillance colleagues to identify SBV infection when it first emerged more than 10 years ago.

Telephone numbers and other contact details for your nearest APHA veterinary investigation centre or non-APHA partner postmortem examination provider can be found at apha.defra.gov.uk/vet-gateway/surveillance/diagnostic/national-network.htm

You can sign up to receive disease alerts direct from the APHA by emailing sui@apha.gov.uk with the county you live in, and your mobile phone number

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