Winter diarrhoea

WINTER DIARRHOEA

Winter Diarrhoea is a highly contagious disease characterised by a brief attack of severe diarrhoea and sometimes dysentery which occurs during the colder months of the year.

AETIOLOGY

Current evidence suggests that a coronavirus is responsible.

PREVALENCE

This disease is quite widespread and has been reported in North America, Britain, Sweden and Australia. The disease can be the cause of serious economic loss in dairy herds, for although the mortality is very low the disruption of milk production and loss of body condition are important factors

CLINICAL FINDINGS

The disease is most serious in adult milking cows, particularly those which have recently calved. Young stock usually only show mild signs but diarrhoea can be present in calves as well as adults.

The diarrhoea is very profuse, watery, homogeneous and dark green to black in colour. There is no mucus or epithelial shreds in the faeces but up to 10% of affected cows may have severe dysentery. A marked fall in milk yield occurs and this may last for up to one week. The consistency of the faeces returns to normal within 2-3 days. Very occasionally an odd cow may develop a very severe persistent diarrhoea which results in death.

EPIDEMIOLOGY

The disease occurs in housed dairy cattle in the late autumn, winter, and occasionally spring. In Britain it most frequently occurs in November, 2-3 weeks after housing. Young, newly-calved heifers or heifers in late pregnancy are most severely affected. Older ones are less severely affected and young stock are unlikely to be affected at all. The disease has a very high morbidity and it spreads rapidly throughout the adult herd, with the majority of animals becoming ill within 7-10 days of the first case. However the disease has normally subsided completely within 2-3 weeks of its initial appearance. The disease is thought to be introduced to a farm by recently acquired infected cattle or visitors. The infection of individual animals occurs orally by the ingestion of either contaminated water or feeding stuffs. The incubation period is 3-7 days.

DIAGNOSIS is therefore based on:

An epidemic occurring during the colder months when cows are housed.
A rapid spread of the disease from animal to animal.
No consistent rise in body temperature during the diarrhoeic phase.
Recovery of the majority of affected animals within one week.
No fatalities.
Confirmation of the presence of coronavirus in the faeces.

TREATMENT

Most affected animals recover without intervention although tylosin and nitrofurazone could be used. Occasionally in severe dehydration, fluid replacement may be contemplated.

CONTROL

Because of the explosive nature of the disease, effective control measures cannot be recommended. An immunity which persists for about 6 months is said to occur after a natural attack but outbreaks seldom recur in the same herd within 2-3 years.

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