Optimizing vaccination strategy

Niamh Field Teagasc, Animal & Grassland Research and Innovation Centre, Moorepark, dicusses Optimizing vaccination strategy. She covers the role of vaccines, deciding on a vaccination programme for Infectious diseases and the practical considerations as part of the Teagasc Virtual Dairy Conference

Summary

• Vaccines should be used as part of an overall infection control strategy
• Both diseases already present in the herd and those that are a risk for introduction into the herd should be included in a vaccination programme
• Planning ahead with a herd vaccination calendar is useful to ensure the vaccination programme is as effective as possible.

Role of vaccines

Whether an animal becomes infected with a virus or bacteria is a balancing act between the animal’s immune response and the strength of the challenge by the infectious agent. Biosecurity and hygiene measures are important to reduce the infectious challenge. On the other side of the balance, colostrum management, nutrition and stress all influence whether the animal’s immune system can effectively fight off a virus or bacteria. Vaccines help to strengthen this side of the equation, by boosting the immune response against a specific infection. Vaccines greatly reduce the risk of clinical disease in a herd; however, they are only one side of the equation, and cannot offset the requirement for biosecurity measures to reduce the burden of infectious agents on a farm.

Vaccination programme

There is no one-size-fits-all approach to deciding on herd vaccination programmes. The veterinary practitioner for each herd should be consulted to advise on the best approach, considering both infectious diseases present already and those that are a risk.

Infectious diseases present in the herd

It is important to identify the diseases that are already circulating in the herd when planning a vaccination programme. Some have obvious clinical signs, such as abortion caused by salmonellosis, while others can have more subtle impacts. Subclinical infection with IBR is common and can cause milk drop, immunosuppression or infertility that may not be noticeable. Bulk milk tank antibody testing or cohort blood sampling can be used to screen herds for various infectious diseases that could be causing subclinical disease. The objective when vaccinating for diseases present in the herd is to stop the spread of the infection and to prevent clinical disease. Vaccinating adult animals for IBR will help to reduce clinical disease and shedding of virus, while vaccinating young stock and calves will prevent the formation of new carrier animals, and over time will help to eradicate the infection from a herd.

Risk of infectious disease in the herd

A vaccination programme should also consider those infectious diseases that may not be present in the herd, but pose a risk to herd health if an outbreak occurs. Leptospirosis is an extremely common infectious disease in Ireland that is present in a high proportion of herds. As such, if leptospirosis is not already present in a herd, there is a high risk of introducing the infection through purchasing an infected animal or from environmental sources. In contrast, BVD virus is very uncommon in Ireland at present and the risk of introducing the virus into a herd is low. However, an outbreak of BVD in a naïve herd could have severe consequences. In this situation, a herd that purchases animals regularly from various sources may be advised to vaccinate, whereas a herd that operates a strict closed herd policy may decide to stop vaccinating.

Table 1. Common infectious agents in cattle and timing of vaccines for each

Practical considerations

Table 1 summarises common infectious diseases affecting cattle in Ireland for which vaccines are available. All animals at risk of disease should be given a vaccine course. For IBR, this includes young stock and sometimes calves, in addition to adult animals. For BVD and leptospirosis, pregnant animals are most at risk. The veterinary practitioner for the herd can advise which animals to vaccinate for each disease.

It is important to plan ahead and identify the correct time windows for each vaccination. Most vaccines require a primary course of two shots in young stock or when given for the first time. Some vaccines are most effective when given at certain times of the year (Table 1). Planning the annual programme for the herd with a calendar is very useful to ensure boosters are not missed and the vaccines are as effective as possible.

Niamh Field, Teagasc Research Officer gives an insight into the role of vaccines, deciding on a vaccination programme for infectious diseases and the practical considerations in this clip, which was recorded as part of the Virtual Dairy Conference 2021.

This article was produced as part of the two-day Virtual Dairy Conference 2021 which took place on 23 and 24 November.

The complete Dairy Conference Proceedings can be viewed here and the individual articles will be published on Teagasc Daily throughout the week.