The latest set of results from the Department of Agriculture, Food and the Marine’s (DAFM’s) national surveillance of dairy herds has found that 79% of milk bulk tanks are testing positive for infectious bovine rhinotracheitis (IBR) gE (a genetic marker) antibodies.

Since 2019, the DAFM has undertaken national surveillance of dairy herds for IBR gE antibodies using bulk tank milk samples, with two rounds of testing/year being carried out each spring and autumn.

The detection of antibodies is a useful and cost-effective tool for the monitoring and control of diseases.

IBR

The application of bulk tank milk (BTM) as a herd-level diagnostic tool has been used extensively in IBR disease control programmes around Europe.

The collection of samples is cheap and easy, and helps to reduce the cost of surveillance programmes, according to Animal Health Ireland (AHI).

A positive IBR gE BTM test result is obtained in herds with moderate to high prevalence of latently infected animals, with ongoing circulation of the virus.

Once an animal becomes infected with IBR, the virus becomes latent and the animal remains an infected carrier for life, developing antibodies that are detectable in blood and milk samples.

Detecting animals that are antibody-positive can be an indicator of an IBR infection within a herd.

An animal that is positive for the antibodies is then a carrier of the virus and can potentially spread it to other animals in the herd.

However, there are exceptions to this, as a calf may have been given antibodies from their dam and non-infected cattle vaccinated with non-marker vaccines.

Control

There have been some positives from the control programme, one being that IBR vaccine sales increased during the past few years (over 3.1 million doses were sold in 2021).

This, according to AHI, should be contributing to a reduction in the proportion of carrier animals in infected herds.

However, it has not yet resulted in a reduction of the proportion of herds with positive bulk tank results.

The virus it typically spread by close contact with an infected animal, although airborne spread is also possible at a distance of up to 5m.

IBR can also be spread via contaminated semen, equipment and people.

Symptoms of a possible IBR outbreak include:

  • Dullness and reduced appetite;
  • High temperatures and rapid and loud breathing – sometimes with coughing;
  • Fluid discharge from nose and eyes;
  • Inflammation of the throat;
  • On occasion, death.

An outbreak of the disease will also have an impact on herd production, with reduced milk yields and abortions possible.

It is also possible to have a sub-clinical infection within a herd, with the first signs of an issue being reduced yields and poor reproductive outcomes.