The month of April is high-season for calf scour in our practice. At this time of year, we treat many calves with calf scour, often involving administering an intravenous (IV) drip to the calf due to the fact that they are severely dehydrated.

Calves become dehydrated because the volume of liquid which they are excreting in their faeces exceeds the volume of liquid which they are absorbing from the gut.

Usually, this process of dehydration takes place relatively slowly, the calf having had a scour for two to three days or more. Recently, we have seen a number of cases of severe scour in newborn calves within 12 to 24 hours of birth. One such case I attended recently was an extremely dehydrated calf born 18 hours earlier. The calf required urgent rehydration by means of an IV drip, together with antibiotics.

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These cases of severe watery diarrhoea in calves less than two days of age are usually caused by E coli.

The widespread use of calf scour vaccines in cows in recent years has meant that this form of scour has not been as common as it was 15 or 20 years ago. However, other forms, particularly due to cryptosporidia, seem to be on the increase.

Cryptosporidia cannot be prevented by vaccinating the cow before she calves, and it would seem that the increased awareness of cryptosporidia on farms has led to reduction in the use of scour vaccines against other forms of scour.

It can be quite frustrating to be vaccinating against a disease such as calf scour, but still be seeing many calf scour cases on the farm due to cryptosporidia. This often leads to the feeling that the vaccine is a waste of time.

However, in many cases, the situation may have been much worse on the farm if two or more agents (eg rotavirus and cryposporida) were present at the same time.

Accurate diagnosis of the cause of disease is extremely useful in deciding how to treat and manage the disease, but when deciding whether or not to vaccinate, consideration needs to be given to what may happen in the future, and not just what has happened in the past.

John Gilmore is a practising vet and managing director of FarmLab Diagnostis, an animal health testing laboratory. See www.farmlab.ie.