Antibody key to PMWS
By Marianne Curtis
SOW immunity to porcine circovirus 2 (PCV-2) is an important factor in determining whether pigs from a particular sow develop post weaning multisystemic wasting syndrome (PMWS), according to a recent Northern Irish study.
The study, conducted by Gordon Allan, principal scientific officer at the Department of Agriculture and Rural Development in Northern Ireland monitored 90 piglets from four sows and four gilts.
Sows and gilts were tested to determine antibody levels to PCV-2 in their blood and piglet antibody levels were checked at three days old. Piglets were monitored throughout the growth period and any deaths were autopsied, says Dr Allan.
"Three mothers had high antibody levels and none of their piglets got PMWS. One had low antibody levels and six out of the 10 piglets dying in the study were from this sow. The remaining four deaths were piglets from sows with intermediate PCV-2 antibody levels."
Differing antibody levels in sows and gilts reflects the degree to which they have been exposed to virus, says Dr Allan. "Multiple exposures mean higher antibody levels."
This helps explain why PMWS mortality decreases in some herds after the initial outbreak, as replacement stock develop immunity which is passed on to piglets, he says.
However, some bought-in gilts may have low immunity, he suggests. "It should be possible to test PCV-2 blood antibody levels of bought-in gilts, but I am not aware of anyone doing this at present."
Dr Allans study may also help to explain why total cross fostering works in some circumstances. But Suffolk-based vet Jake Waddilove urges caution. "Total cross fostering involves allowing piglets to suckle from their own mother initially, then all are removed and randomly distributed between lactating sows. The idea is to equalise immunity to PMWS.
"However, level of success varies between farms. On those where sows have equal levels of immunity, it will have no benefit. But for herds with a variable level, it could be applicable. It is best to seek vet advice, as it could aggravate PMWS in some circumstances."
Dr Allans study also raises hopes that vaccination will be possible, says Mr Waddilove. "The science has already been done, so vaccination is theoretically possible. But it will have to be proven at field level and fulfil legislative requirements. So it is likely to be a year or two away." *