Animal Health Ireland, in association with Teagasc, has recently completed a pilot screening programme to assess the prevalence of infectious bovine rhinotracteitis (IBR) in Irish beef herds.

Dr Maria Guelbenzo, AHI, presented the results today at the Teagasc national beef conference in Tullamore.

What is IBR?

IBR is a disease caused by a virus called Bovine Herpes 1 (BOHV-1). IBR is found worldwide and in addition to issues around health and liveweight gain of animals, it can also have an effect on the trade of animals and semen.

From an Irish perspective, IBR is prevalent on most cattle farms with 75% of animals exposed to IBR in their lifetime.

How do I know my animals have IBR?

Cattle with IBR have a watery discharge from the nose and eyes, with the face often being tear-stained. Animals may have a red nose and eyes and lack of appetite. Affected animals may be dull, off their feed and have a high temperature (107°F to 108°F/41.7°C to 42.5°C).

The severity of the clinical signs can depend on the animal husbandry, stocking rate in sheds, degree of stress and age.

Where an outbreak occurs in a herd which has not had exposure, deaths can occur very quickly.

The virus is mainly spread directly by close contact between animals. The nasal discharge from infected animals can contain very high levels of virus and as a result infection can spread rapidly through a herd when susceptible cattle come in contact with infectious cattle.

Latent carriers spreading disease

Dr Guelbenzo explained that the disease is quite complicated in that although recovery following initial infection is associated with the development of immunity, this does not eliminate the virus. Instead, the virus establishes lifelong latent infection in the nerve cells within the animal’s brain.

During this period, the latent carrier is not shedding virus.

However, at times of stress such as transport, calving, nutritional stress, mixing stock, etc, the virus may be reactivated and can begin to multiply and be re-excreted, generally from the nose and eyes. This leads to new infection in other susceptible cattle, which in turn will also become latent carriers.

Cattle purchase

IBR is seen as a particular issue in herds where animals are purchased from multiple sources and mixed after purchase.

Transport and mixing can increase stress levels and result in outbreaks of IBR following reactivation of latent infection and spread to susceptible animals. Vaccination, (ideally in advance of movement or on arrival on farm), along with measures to reduce stress during transport and following arrival can help can help to control these outbreaks.

Pilot programme results

The pilot programme consists of the sampling and testing of a proportion of the herd for IBR, application of an IBR on-farm veterinary risk assessment and management plan (VIBRAMP), and provision of biosecurity and disease advice.

The VIBRAMP consists of a questionnaire that captures details of the farm structure, animal movements, biosecurity and vaccination history, with the vet and herd owner agreeing up to three changes to improve biosecurity.

Herds are initially screened by applying a herd "snapshot", which requires the sampling of 30 randomly selected animals over nine months old that are used or intended for breeding.

So far, 25 herds in 22 counties have been tested. Between 15 and 44 samples per herd were submitted.

Sixty per cent (15) of the herds had a negative (zero or one seropositive animals) and 40% (10) had a positive (two or more seropositive animals) snapshot test. No seropositive animals were found in the snapshot from eight herds. Six herds had one, three had two and six had between three and seven seropositive animals.

The maximum number of seropositive results found in one herd was 14 out of 30. So far, a large proportion of the seropositive results were from older, non-homebred animals.

Conclusions

Dr Guelbenzo confirmed at the Teagasc beef conference that results to date show that 60% of the tested herds are likely to have a low prevalence of infection.

Table 1 outlines the summary results. These herds would be the best positioned to progress towards an IBR-free status by testing the remainder of the herd and either confirm freedom or remove seropositive animals.

For the remainder, complete and regular herd vaccination can be used as one of the measures to control IBR in an infected herd as it makes it less likely that a latent carrier will reactivate and shed the virus.

It will also be less likely that a naïve animal will become infected and spread the virus after exposure. However, Dr Guelnbenzo stressed that this meant vaccinating the whole breeding herd and not just young stock to achieve success.

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