Veterinary advice: Hidden IBR virus flares up in cattle when they are stressed

IBR has been with us for quite a while (since 1989).

It is a herpes virus, and like another herpes virus, the common cold sore, once you get it, you have it for life.

It flares up in cattle at times of stress, like calving, bulling, weaning, inclement weather etc, causing an awful lot of shedding of new virus.

Clinical signs are associated with the first time an animal gets the disease.

The virus damages the lining of the nose and upper airways and windpipe, resulting in the lining falling off.

The animal can have fever, depression, lowered milk yield, respiratory signs (breathing fast, snoring, red nose, snotty nose), and sore eyes, and be off its feed.

It also has a marked immuno-suppressive effect, meaning the animal is wide open to secondary bacterial infections. Infection during pregnancy often results in cows aborting. The cow can pass it via the blood to the unborn calf in its womb.

During the initial infection, the virus enters the nerves of the head and hides out in places like the tonsils.

Following recovery from the initial infection, this animal becomes a latent carrier with antibodies, showing no signs of the disease.

The virus will be reactivated once the animal comes under stress.

The antibodies can be identified in blood and milk samples.

Losses come from death, reduced productivity, reduced thrive, abortions, infertililty, labour, drugs and veterinary bills.

One estimate has normal cows with IBR antibodies producing 2% less milk per year.

Many countries in Europe have achieved IBR-free status, and many more are working towards it.

These countries will not accept animals from Ireland if we do not reach the same status as them. Our export markets will be eliminated.

About 80% of dairy herds have tested positive for IBR antibodies in bulk milk testing, and 75% of beef herds are positive.

So what do you do next? You should talk to your vet about your situation. An investigation should be carried out to see what level of IBR you have in your herd.

Bulk milk testing can be carried out initially, as an indicator of herd status. Blood sampling is more accurate than milk sampling for identifying individual animals.

Once your category is established, a control plan can be put in place.

Any control plan must include the following.

Bio-exclusion

n Only buy IBR test negative animals.

n Isolate bought-in animals for two weeks.

n Prevent exposure to neighbouring stock.

n Disinfection of visitors, equipment and vehicles, machinery.

Isolation/culling policy

n In herds with very few latent carriers, isolation of these animals may be achievable preventing spread to other healthy animals.

n To become IBR-free, test positive animals should be removed from the herd.

Vaccination programme

n With vaccination, IBR-negative animals are less likely to contact the disease and IBR positive animals are less likely to spread the disease.

All vaccines licenced for use in the Republic of Ireland are marker vaccines, and the antibodies they produce can be differentiated from those produced to combat the natural infection. However, animals bought in from other jurisdictions may have been vaccinated by conventional vaccines, and these cannot be differentiated from the natural infection.

Irish vaccines come in live and inactivated formulations, and each has its advantages. Both will reduce clinical signs of IBR, both reduce shedding of the virus. Discuss choice with your vet.

Once the control plan is in place, monitoring should be routinely done to evaluate progress, by bulk tank sampling or blood testing young stock, or both.

AI stations will not accept a young bull with IBR antibodies, this animal should be isolated, and not vaccinated. Separate syringes, needles and other equipment should be used for these animals.


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