Swine influenza virus (SIV) continues to plague our swine industry, and the results are often economically catastrophic.

Moderate to severe weather changes, especially in the spring and fall, account for the majority of stresses that trigger the clinical outbreaks of this disease.

We continue to see outbreaks across the Midwest due to this year's unusual summer weather fluctuations.

We have also seen that age holds no limits on the disease. Nurseries, grow-finishers and sow units are all affected, making the “quieting” of the herds much more difficult.

Case Study No. 1

I was called to a 1,000-head finisher with a severe cough and lethargic, off-feed and feverish pigs.

The facility is a totally slotted, double-curtain-sided barn with all-in, all-out (AIAO) production. The pigs weighed about 60 lb. and had been placed in the unit 10 days earlier.

Two pigs died suddenly and a necropsy indicated Streptococcus suis. The pigs were placed on water medication. Diagnostics confirmed the presence of Strep suis. SIV was also isolated from nasal swabs.

The cough continued for 7-10 days with some pigs developing chronic pneumonia and becoming poor-doers.

At closeout, death loss was 3%, while 6% of the pigs ended up as culls.

After the finisher was empty, it was cleaned, disinfected and refilled. Incoming pigs were given SIV vaccine twice, upon arrival and again in two weeks.

Upon further investigation, neither the sow herd source nor its off-site nursery showed any clinical signs of SIV. Further diagnostic tests showed the sow herd to be negative for SIV.

Another finishing unit nearby had broken with SIV recently, so area spread was suspected as the cause of SIV in this finisher.

Case Study No. 2

A 1,200-sow, farrow-to-wean operation experienced erratic farrowing rates for three months, from 65% to a high of 83%.

This 5-year-old unit has averaged 20 pigs/sow/year.

The breeding facilities are excellent, and the breeding management team does a very good job with heat detection and insemination techniques.

The isolation/acclimation (I/A) of incoming breeding stock is done off-site and appears adequate. New gilts and boars are held 45-60 days in I/A before moving into the breeding barn. They are given a prebreeding vaccine prior to movement into the sow unit.

When reviewing the breeding records, the Parity 1 and 2 females showed the lowest farrowing rates, averaging 70%.

Blood tests revealed the herd to be positive for H1N1 and H3N2 SIV, but serological levels varied drastically. This is common in younger animals.

Records indicated early resorption and abortion primarily in the younger females, with a few false pregnancies.

Feed samples were also taken, and zearalenone mycotoxins were found at mild to moderate levels. Feed bins were cleaned out and mold inhibitors were added to sow feeds.

The breeding herd was vaccinated for SIV twice, two weeks apart.

New breeding stock is vaccinated twice while in the isolation unit.

Since this incident, farrowing rates and herd health are improving.


As we continue to strive for better control of SIV, it will demand more stringent measures:

  • AIAO production;

  • Strict biosecurity;

  • Farm-specific vaccination protocols targeting all phases of production;

  • Limited commingling, especially in postweaning phases of production;

  • Altered management schemes as needed to minimize stressors such as empty feeders, ventilation problems, plugged waterers, etc.;

  • Better understanding of various disease actions and interactions; and

  • Proper I/A of incoming breeding stock. Lack of proper I/A and area spread continue to be the primary sources of infection and reinfection.

When viral load becomes high, the disease will often manifest itself.

Due to the immunosuppressive nature of SIV, we often see other disease entities, including but not limited to: Streptococcus suis; Haemophilus parasuis; Mycoplasmal pneumonia; porcine reproductive and respiratory syndrome (PRRS); and other respiratory, enteric and systemic disease complexes.

Every herd's experience with SIV is different due to the various levels of immunity within subpopulations.

Remember, whatever vaccination protocol you choose, the potential for failure exists because of constant changes in strain variation and the growth of mutant strains.

With these developments, commercial and farm-specific autogenous vaccines are our options.

If you are fortunate enough to have a homologous (similar) strain in the vaccine that you are using, then your chance for success is improved.

Work closely with your veterinarian to establish the diagnostic tools and database for your herd.