IBR infection is very
The current estimate is that between 70-80% of beef and dairy herds in Ireland are endemically infected, with adult cows being latent carriers of infection.
IBR is not commonly seen in young calves below three months of age, probably due to the good protection afforded by colostral antibodies.
In most dairy herds, calves are removed from dairy cows very shortly after birth and reared separately. Therefore they may remain “clean” or “naïve” throughout the rearing and first breeding season until they mix with the lactating cows after first calving. This is a very stressful time for dairy heifers, which makes them more susceptible to disease if the virus is endemic in the herd. Therefore in many dairy herds the common disease pattern is that heifers become infected when they enter the milking herd.
What causes IBR?
‘IBR’ stands for ‘Infectious Bovine Rhinotracheitis’ and is caused by Bovine Herpes Virus 1 (BoHV1).
Primary infection occurs when a naïve animal is exposed to the IBR virus through the nose or mouth following direct contact with an animal shedding the virus, or indirectly via fomites or airborne transmission and is commonly associated with clinical signs of acute IBR disease which range from mild to severe.
As IBR is caused by a herpes virus, not dissimilar to the human cold sore virus, it means that once an animal has been infected, it will become a latent carrier for life. Latent carriers are a potential source of infection and can shed virus at times of stress (i.e. transport, calving, nutritional stress) resulting in disease in in-contact animals.
Clinical signs of IBR are variable ranging from subclinical disease to high body temperature, severe upper respiratory tract disease (the virus will target the eyes, nose and throat) and reproductive disease with symptoms of infertility and abortion. In adult dairy cows sudden reduced milk production can be a feature of the disease.
A recent study showed that dairy cows infected with IBR produced 2.6l/day less milk than uninfected animals over the lactation. That equates to an annual loss of almost 1000kg of milk/cow. Such losses are not sustainable.
Is your herd infected?
Animals with latent infection will have antibodies against IBR that can be detected in blood and milk.
Establishing the disease status can be done through bulk milk antibody testing, targeted blood or milk sampling.
What is a Marker Vaccine?
A Marker IBR vaccine is one which allows the differentiation of animals infected by wild type virus from those which have been vaccinated.
Vaccination with an IBR Marker vaccine has the advantage of not only protecting animals from clinical disease, but also allowing the herd to be monitored for infection. For herds in accreditation programmes or who want to eradicate IBR the ability to monitor for natural infection is essential. Specific tests are used which will only detect the antibodies generated from infection with wild virus.
An animal which has received a Marker IBR vaccine but has not been exposed to wild virus will test negative. This can increase market opportunities for some farmers. Note though that bulls destined for bull studs selling semen straws into European markets must be totally free of IBR antibodies, including marker vaccine antibodies, so should not be vaccinated with any IBR vaccine. Both live and inactivated marker IBR vaccines are available.
What is the difference between a Live IBR vaccine and an Inactivated IBR vaccine?
Live IBR vaccination (Rispoval ®IBR Marker Live) should be used to protect naive and high risk animals against clinical signs of disease. Inactivated IBR vaccines (Rispoval®IBR Marker Inactivated) are more effective than live vaccines in reducing viral shedding by latently infected animals.
A straightforward Rispoval® IBR-Marker Vaccine two-step programme is now licensed to reduce clinical signs and viral shedding and, in female cattle, to prevent abortions associated with BoHV-1 infections for up to 12 months. Animals at three months of age or older at first vaccination should be given one intramuscular injection of Rispoval® IBR Marker Live followed by a single booster of Rispoval® IBR Marker Inactivated (given subcutaneously) within six months to provide a duration of protective immunity of 12 months. Thereafter, single booster vaccinations should be administered every 12 months (see graphic above).
STUDY DEMONSTRATES A REDUCTION IN PREVALENCE OF IBR IN A DAIRY HERD THROUGH VACCINATION
An ongoing study in a closed 220 cow dairy herd in Scotland using Live IBR Marker vaccine in heifers and Inactivated IBR Marker vaccine in cows has generated some interesting field data, demonstrating how use of this combination vaccination programme can protect naïve animals from wild type IBR infection in the face of a high herd prevalence. The breeding herd (all cows, pregnant and bulling heifers) were vaccinated initially with Rispoval®IBR Marker live, followed by Rispoval®IBR Marker Inactivated and then boosted annually with Rispoval®IBR Marker Inactivated.
In subsequent years the bulling heifers received Rispoval®IBR Marker live, and Rispoval®IBR Marker Inactivated before breeding and were then boosted annually with Rispoval®IBR Marker Inactivated.
At the start of the study in 2012, 99% of the milking herd were infected with wild type IBR. On this farm, the young stock are housed and grazed separately from adult cows until late pregnancy. For the last two years the IBR status of the youngstock has been tracked as they join the adult dairy herd.
The aim is to protect the youngstock from IBR infection using the vaccine, and eventually replace all of the latently infected older cows with protected heifers. So far the vast majority of heifers that tested seronegative for IBR antibodies prior to entry into the milking herd have remained seronegative to the wild-type IBR virus as shown by subsequent individual milk testing.
Alongside the normal herd culling policy using the two-step live/inactivated vaccination programme has reduced the percentage of infected animals in the herd from 99% to 45% in a three year period. This study is ongoing, but results to date suggest that this combined vaccination approach is proving effective in protection against both clinical disease, and latent infection in the incoming heifers. Eradication of IBR could be achieved within five-six years of initial diagnosis by removing residual latent carriers.