IBR is present in most dairy herds1 as well as many beef herds. Infection in naïve animals (animals which haven’t met the virus before) can be particularly severe with signs ranging from fever, eye and nasal discharges, milk drop, abortion and in some cases death.
For both naïve and latently infected animals, vaccination is the gold standard for IBR control. Vaccination boosts immunity protecting naïve animals from disease and reducing shedding of virus by latent carriers. It should be used alongside other management measures, in particular biosecurity.
There are a number of different types of IBR vaccine available. Choice depends on the particular farm situation, age of animals and disease threat:
- Marker or conventional
- Live or inactivated
- Monovalent vaccines (which protect only against IBR) or multivalent respiratory vaccines (which protect against IBR and other respiratory viruses)
A marker vaccine is one in which a non-essential protein has been removed from the surface of the virus used in the vaccine. This doesn’t affect the effectiveness of the vaccine, but it means that antibodies produced to the vaccine can be distinguished from those produced following infection with ‘wild’ virus. This enables a distinction between animals which have been vaccinated and those which have been previously infected.
This distinction is important in herds wishing to become accredited, or IBR free, or for pedigree farmers wishing to sell stock or semen.
Marker vaccines also improves the ability to monitor animals or herds to identify changes in IBR status, so they are the vaccines most frequently used in breeding animals.
LIVE VS INACTIVATED VACCINES
Vaccines can be either Live or Inactivated (also sometimes referred to as ‘killed’ vaccines).
Live vaccines help establish rapid immunity, which means they are useful in situations where rapid protection is required, such as for bought in animals. For the most rapid response a live vaccine, where possible, should be given intranasally.
Live vaccines as well as working rapidly also stimulate immunity most similarly to natural infection. This is because the virus is live (but altered to make it safe) so it can replicate in the body and therefore the body responds to it most similarly to the way it would to infection. Studies have found that live vaccines are better at protecting naïve animals from clinical disease compared to inactivated ones2.
Best used in: Naïve animals
Aim: To protect animals from clinical disease
Inactivated vaccines as the names suggests, contain inactive or killed virus. This means they stimulate immunity slightly differently to the live vaccines, and have been found to be better at reducing viral shedding in animals which have previously been infected and are carrying the virus (latently infected animals)3. In a dairy herd with a high bulk milk antibody level, which suggests that a high proportion of the milking cows are already infected, use of an inactivated vaccine can better help to reduce the amount of virus these cows shed when under stress. This reduces the risk to any uninfected animals, or heifers entering the herd.
Best used in: Latently infected animals
Aim: To stop/reduce viral shedding.
VACCINATION PROGRAMME EXAMPLE
Whilst the above outlines differences in the way live and inactivated vaccines work and when they should be used, the reality is that when starting a herd vaccination programme, unless embarking upon an IBR accreditation or eradication programme, it is unlikely that all individual cows will be blood tested to determine whether or not they have previously been infected. And a vaccination programme needs to be capable of being implemented at farm level without being too complex. Therefore, below is an example of a breeding herd vaccination programme utilising the Zoetis Rispoval IBR-Marker vaccines (Rispoval IBR-Marker Live and Rispoval IBR-Marker Inactivated).
Rispoval IBR Marker Live can be used from 2 weeks of age. In herds with good colostrum management, colostral antibodies are known to give good protection against IBR for the first few months of life, so commonly vaccination against IBR commences from 3 months onwards. Whilst heifers are often managed separately to the main herd, IBR can be spread via fomites (ie on clothing, machinery etc). IBR is known to affect follicle development, and therefore conception rates, particularly in naïve animals, heifers should therefore ideally be vaccinated prior to first service.
Assuming most heifers will be naïve, i.e. not have been infected previously, they start their vaccination programme with a single dose of live vaccine (Rispoval IBR Marker live). This is followed up to 6 months later with a booster dose of Rispoval IBR-Marker Inactivated, after which protection lasts for 12 months, so for ongoing protection animals require a single booster dose of Rispoval IBR-Marker Inactivated annually.
This combination of a live and Inactivated vaccine gives a more complete immune response and provides 12-months protection from a single booster dose given annually.
Of course each farm situation is different, and therefore veterinary advice should be sought on the most appropriate vaccination programme for your herd.
Next we’ll look at a case example.