During the past decade, PRRS (porcine reproductive and respiratory syndrome) has been a major cause of abortions and reproductive disruptions.
In the last year, there have been reports of abortion “storms” caused by PRRS. Recent episodes in Minnesota have produced deaths of 50% in nursing pigs, 30% in nursery pigs and up to 15% of sows, similar to what occurred several years ago in Iowa.
It's easy to blame reproductive failure on PRRS. There are many causes for abortion and reproductive failure. Some causes are infectious, some are non-infectious.
Non-infectious causes of infertility should be suspected if no disease appears present, there are no abortions, mummies, and stillbirths, and if the problem is gradual or long-term.
A single factor, such as a toxin (zearolenone, aflatoxin), may be to blame. But usually multiple deficiencies cause failure.
Conduct a thorough, on-farm investigation to identify possible deficiencies. Analyze production records, observe the herd, monitor daily tasks and interview farm staff.
Case Study No. 1
A 600-sow herd had a 60% pregnancy rate. The owner was worried about PRRS lowering breeding and farrowing rates. Staff reported a large number of females returning to heat at unusual intervals. They didn't notice any change in abortions or quality of pigs farrowed.
An investigation revealed staff had little field experience, but were very knowledgeable people. They “knew” sows came into heat five days postweaning. Sows were artificially inseminated that day. Staff failed to recognize the need for heat detection or how to determine when a sow was in heat.
While this problem could have been caused by an infectious disease, clinical evidence strongly suggested that improper breeding procedures created reproductive failure. Many sows were artificially inseminated (AI) that weren't in estrus.
The solution was an intense training program for the unit staff and regular review of the farm records. Part of the solution included taking sows to a location to be directly exposed to a boar. This protocol allowed unit staff to observe what sows in estrus looked like so AI was more correctly applied.
Case Study No. 2
A 300-sow, farrow-to-feeder pig operation experienced an abortion storm. About 30 sows aborted at 40-95 days of gestation during a two-week period. The herd was PRRS-positive and thought to be stable. Herd additions brought in every two months had come from the same source for several years. There was no information from the source farm that there had been a change in health status.
During the abortion episode, blood samples were collected from sows that had aborted and nasal swabs were collected from affected animals. The owner was convinced his herd was experiencing a PRRS outbreak and insisted the herd be vaccinated.
Laboratory results revealed nasal swabs were positive for H3N2 swine influenza virus (SIV). Paired serum samples (same animals checked two weeks apart) verified that the SIV titers went from negative to more than 640.
The paired samples also showed no change in PRRS ELISA (enzyme-linked immunosorbent assay) serum levels and no PRRS virus was found.
Further investigation revealed that the source farm of the incoming gilts had recently become infected with H3N2 SIV.
As a result, the only federally licensed, bivalent vaccine for SIV was added to the farm's vaccination program. The bivalent vaccine contains both common strains of SIV found in the United States, H3N2 and H1N1. Incoming gilts were given SIV vaccine by the supplier prior to shipment to the recipient farm.
From this experience, the herd owner learned the importance of laboratory diagnostics.
Reproductive failure as evidenced by abortions is a serious matter. Getting a definitive diagnosis is paramount to establishing preventive protocols. Appropriate sample selection, which generally should include materials other than aborted fetuses, is important to achieve correct diagnoses.
It is important to establish whether or not the sow was sick before she aborted. When sick sows abort, the cause is usually the result of systemic illness in the sow rather than fetal infection. Thus, serum samples, PCR (polymerase chain reaction) test on pooled serum samples, and lung tissue from dead or euthanized sows have the greatest odds for verifying the cause. PRRS continues to be the major cause for abortions in sow herds.
Accurate diagnoses using good scientific principles and tools will lead to more better preventive procedures.
Not all abortions are caused by PRRS. Make sure you know what is going on before spending money on the “wrong” cure.