Whole-herd vaccination critical to long-term PRRS management
Vaccinating entire herds against porcine reproductive and respiratory syndrome (PRRS) is crucial to ensuring the virus doesn’t become untreatable in the future, says a UK veterinarian.
Joseph Lunt of Oakwood Veterinary Group, Norfolk, said the PRRS virus’ ability to evolve during a single outbreak runs the risk of new strains developing.
This theoretically could make existing vaccinations less effective against those mutated strains, with knock-on effects for pig-herd health, welfare and profitability.
Following a Zoetis Young Pig Event in Hatfield, Hertfordshire, Lunt said virus evolution could be a threat on farms where the virus isn’t properly protected against.
But with simple changes in vaccine regime and management, the virus can be prevented from replicating, cutting its ability to mutate.
“If farmers are seeing persistent signs of the disease in their herd, this could indicate that virus replication is still occurring,” he said.
“Because it’s an ever-evolving virus, it’s important that treatment is carried out across the whole herd — which includes vaccinating vulnerable young stock as early as possible to ensure PRRS immunity.”
According to Laura Hancox, DVM, a swine veterinarian at Zoetis, the key for farmers is to remember that PRRS virus needs a susceptible pig to multiply and survive.
“If all animals are immune at once, then the virus has nowhere to replicate, and the herd should become PRRS virus-negative,” she said.
On farms with farrow-to-finish operations on a single site, it’s important to vaccinate piglets to maintain the stability of the breeding herd, she added.
“If you are weaning off-site, you should vaccinate piglets if your breeding herd is unstable as some weaners will be PRRS-positive; also you should vaccinate piglets if you are mixing health status.
“You should also piglet vaccinate if you don’t have all-in/all-out systems or if you’ve got a high risk of PRRS introduction.”
However, it is worth remembering that if piglets come from a PRRS-stable herd — meaning they are virus-negative — and are weaned off-site into a high-biosecurity, all-in/all-out system, then vaccination probably isn’t necessary.
Single live vaccines
On farms where farmers are using one vaccine for sows and another for piglets, it’s important to only use one live vaccine in the same herd, Hancox added.
“Multiple vaccines may be beneficial as multiple strains of vaccine virus will make you more likely to protect against the wild type of the virus.
“But if you do that with multiple live vaccinations, there’s a risk of recombination. Excellent biosecurity will help reduce the risk of the virus spread and recombination, but the important thing is to avoid using different live vaccines.”
To avoid the challenge of using different vaccines across a herd, Hancox said producers can select a single live vaccine which can be given in the same dose to piglets from day 1, as well as to sows and gilts.
“Using a vaccine which can be administered from 1 day of age offers early protection to piglets through to slaughter, and it also simplifies management,” she said.
“It means you can vaccinate piglets when you are handling them for other procedures, which reduces stress, and it’s one less vaccination around weaning.
“In the breeding herd, we recommend gilts get a minimum one dose 4 weeks before breeding and that sows are revaccinated every 4 months.”
She added: “PRRS is not a latent virus; it won’t stay in the pig and the animal will eventually clear it.
“That’s why a whole-herd approach is key to managing the disease and getting it out of a system.”
Posted on February 22, 2019