Tackling PRRS: Managing outbreaks to limit damage
Porcine reproductive and respiratory syndrome (PRRS) is a virus that can take a significant toll on pig producers due to reproductive losses, decreased performance and damaging secondary infections. But according to a new guide on PRRS management, understanding how to manage the costly disease can help improve pig health and welfare, while increasing productivity.1
The guide, which was developed by swine veterinarians at Zoetis UK, says that as with all diseases, preventing the PRRS virus from entering a farm is preferable to trying to deal with it once animals have been infected.
Biosecurity is paramount, both in preventing PRRS from entering a naive herd — one that has never been exposed to the virus and has no immunity — and from stopping a new strain from entering a PRRS-positive herd.
Recognizing the risks
To create an effective biosecurity program, it’s important to consider all of the possible routes a virus could enter a farm, the guide stresses.
These include buying in semen or replacement stock, wildlife, vehicles or farm personnel.
Once those possible points of entry have been identified, it is easier to identify the best practical measures to stop a virus from reaching a herd (see table).
|Risk factor||Best possible control measure|
|Buying in stock||Breed own replacement gilts|
|Buying in semen||Choose one source which regularly tests for PRRS|
|Wildlife||Install wildlife perimeter fencing, bird-proof buildings and carry out pest control|
|Vehicles||Install perimeter fencing so vehicles cannot enter a site|
|Objects which could carry a virus (such as clothes, footwear or equipment)||Ensure no equipment, clothing or footwear is allowed to pass between farms or production stages|
|People||Have a 48-hour pig clean time and showering policy|
|Biting flies||Have a good insect-control policy|
|Aerosol||Install good air-filtration systems|
Controlling an outbreak
If a breakdown in biosecurity leads to PRRS being discovered in a herd, it’s important to remember that there are a number of measures which can be taken to control the virus’ spread and, ultimately, its impact.
The guide notes that PRRS is quite a fragile virus that can survive in cool and damp conditions for several days, but with heat and drying it can be killed quickly.
The virus is also readily inactivated by detergents and disinfectants, so thoroughly cleaning buildings, equipment, clothing and footwear is very important.
Within a breeding herd, controlling PRRS relies on achieving stable immunity, something that can be reached with a vaccination program.
Creating stable immunity pivots on young breeding stock, as their low immunity to the virus means they are often a source of PRRS issues.
If gilts are properly acclimatized before they join the rest of the breeding stock, then it should be easier to maintain stable immunity in the herd, the guide says.
Acclimatizing gilts relies on developing immunity either through exposure to PRRS-infected animals or by vaccination with a live vaccine.
Either of these options should be carried out when gilts are around 2 to 4 months old to give time for immunity to develop before they enter the herd.
When using live PRRS vaccines, all pigs in the same airspace should be vaccinated at once.
Sow and suckling-pig management
Maintaining stable PRRS immunity in sows is best achieved by carrying out an appropriate vaccination program.
With suckling pigs, the target is to limit the spread of the PRRS virus between litters.
According to the guide, this can be managed by restricting cross-fostering to the first 24 hours of life, euthanizing severely affected piglets, and maintaining a strict all-in/all-out policy with no holding back of piglets or moving them from room to room.
Controlling chronic PRRS in weaned pigs can be difficult — and in continuous systems can be almost impossible, the guide notes.
The best starting point is receiving weaned pigs with stable immunity, but this relies on the breeding herd’s management.
In herds that are infected with PRRS, the best strategy is to vaccinate all of the animals or to use all-in/all-out management.
As PRRS affects an animal’s immune system, making it more susceptible to infection, controlling endemic diseases such as enzootic pneumonia, Glasser’s, influenza and porcine circovirus is also an important step in controlling the impact of the virus.
Using a live PRRS vaccine is one of the best ways of building a herd’s immunity to the virus, the guide confirms.
As well as controlling clinical signs of the virus, a vaccine can also reduce shedding of wild-type virus (naturally occurring, non-mutated strains).
Before carrying out a live-vaccine program on pigs that haven’t been vaccinated or exposed to PRRS before, it’s important to consult a veterinarian.
Clearing PRRS from a herd
Eliminating PRRS from a herd can help improve pig health and welfare, as well as increase production and profitability, the guide reports.
Removing the virus from a herd can be attempted by total depopulation and repopulation of a herd, partial vaccination or mass vaccination.
Each of these techniques must be accompanied by strict biosecurity measures to make sure herds don’t become reinfected.
Although it is the most expensive approach, the most thorough solution is to depopulate and repopulate the herd. Where the unit is a farrow-to-finish operation, this is the only realistic option for elimination.
In theory, mass vaccination can be used to eliminate PRRS from a herd as the virus doesn’t persist in immune animals. This is most easily achieved in closed herds where pigs are weaned off-site.
Whatever the situation, however, it is important for producers to talk to their veterinarians to discuss the best vaccination and elimination options for individual businesses, the guide stresses.
For a free download of Zoetis UK’s “Complete Guide to PRRS,” click here.
1 “Complete Guide to PRRS,” http://o.int.zoetis.com/A-Complete-Guide-to-PRRS.html
Posted on October 22, 2018