This is caused by a herpes virus that primarily affects the tissues of the nose and windpipe, and is similar to a severe case of flu. Disease has a variety of forms depending on animal’s age and previous levels of immunity. All ages can be affected and the four main groups of clinical signs are:
Acute respiratory form – this is the classic form of the Disease. It causes a very high temperature, dullness, low appetite, discharge from nose and sometimes eyes. Secondary infection of the trachea can lead to a foul smell,severe cough and “roaring” breathing. Severity can range from mild to death.
Ocular form – can be seen on its own or with respiratory symptoms. The conjunctiva of the eye becomes very dark red and swollen with small ulcers. A white discharge occurs, that can be so severe as to close the eyes and leave a thick layer of pus oozing out.
Abortion/foetal death – can be caused by IBR at any stage of pregnancy, and can be difficult to diagnose. It multiplies in the placenta and may well occur without any of the other symptoms. Abortion occurs some weeks after the initial infection with the virus often having disappeared from the placenta making diagnosis difficult. Cow will however have positive antibody levels.
Milk drop / production loss – There is a strain of the virus that can cause a sudden milk drop with no other symptoms. These cows slowly return to 80-90% yield after a week irrespective of treatment.
Treatment is with anti-biotics and anti-inflammatories, both injectable and topical. This does not treat the virus however, only the secondary infection that accompanies it.
The best method is by vaccination with Bovilis IBR. Once the whole herd has been treated, six monthly boosters are required, and incoming stock must all be treated before entering the herd.
As IBR is widespread in the national herd, one problem is deciding whether to vaccinate or not, especially if animals from different sources have been mixed and only one is showing symptoms. In such a case it is impossible to know which animals have been previously exposed and so have become immune, and so for whom vaccination would be a waste of time.
To be safe however you should always vaccinate the whole group as soon as a case has been confirmed.
Bulk milk samples are a good way of monitoring herd levels of infection. If done every 3 months they can give an idea of the level of infection circulating within the herd. Advice can then be given by the vet, depending on the levels found.