Porcine reproductive and respiratory syndrome (PRRS) virus can affect all stages of the production system, but even if sows and boars are sufficiently protected, the impact can still be felt in the weaners and fatteners.
Maureen Prendergast, swine technical manager at MSD Animal Health, explained: “There are really two parts to the PRRS virus; reproductive and respiratory. We see reproductive issues in breeding stock, but respiratory problems are more common in the weaners and fatteners.”
Boars can infect sows and sows can infect their piglets. Once infected, pigs can shed the virus for extended periods; in saliva for up to 42 days and in semen between 43 and 92 days. Boars have been found to be intermittent shedders, so conclusive testing can be difficult.
When the PRRS virus infects a herd, about 1-3% of sows will abort at all stages of gestation up to 100 days. At seven to 10 days after initial infection, sows in late gestation (100 days plus) will start to farrow prematurely.
This occurs because the virus crosses the placenta and affects piglets in utero. This phase is characterised by an increase in late-term abortions as well as the births of small, weak, stillborn, and mummified pigs.
Many affected sows experience difficulty conceiving and have delayed returns to oestrus and low conception rates. Infected boars can experience a lack of libido and decreased semen quality. A Dutch study analysed the economic-impact of a PRRS outbreak in sow herds and estimated the cost at €126/sow.
The majority of farms in Ireland will be positive for PRRS at some point in the production cycle, so it’s really important that those farms are vaccinating their breeding stock against the disease.
“PRRS virus normally affects sows in the latter stages of pregnancy. If a whole litter is lost as a result of late abortion, that could cost the farmer the equivalent of vaccinating 100 sows per year,” added Maureen.
Secondary respiratory infections
Unfortunately, maternal antibodies do not provide adequate protection to their piglets and any protection they do provide is short lived.
When piglets are not vaccinated, disease can circulate between piglets, second stage and fattener groups, resulting in infection of 95% of finishing pigs on PRRS-infected farms.
The cost to farmers varies depending on secondary infection rates, but allowing for reduced growth rates, increased mortality and reduction in feed conversion ratio (FCR) it has been estimated at around €5/pig.
“Naïve herds will always be at risk of introduction of infection through biosecurity breakdowns, AI, or bought-in stock. In herds where PRRS has been found to be present, it’s recommended that breeding stock are vaccinated to prevent the spread of field virus,” explained Maureen.
“It’s particularly important that incoming gilts are vaccinated for a sufficient time before introduction to the sow herd so that they do not reintroduce infection.
“Piglets can be vaccinated against infection with PRRS from two weeks-of-age offering protection for up to 24 weeks and, of course, administration can be made easier in larger herds with the use of the IDAL vaccination device.”
More information
Farmers should discuss their vaccination regime with their vet who can also advise on improving sow fertility and on-farm biosecurity.
Further information is available from the vaccine SPC, your veterinary practitioner or MSD Animal Health, Red Oak North, South County Business Park, Leopardstown, Dublin 18, Ireland.
MSD Animal Health can be contacted at: 01-2970220; or emailed at: [email protected].
