Swine influenza virus (SIV) has become a major player in the respiratory disease complex.

As a veterinarian serving both large sow units and grow/finish operations in Iowa, Minnesota and South Dakota, I have seen the herd health and economic devastation caused by this disease.

In the past, SIV had seasonal peaks. But, recent observations suggest that it is present year round, increasing the odds that it will spread throughout an operation.

 Barn size 1,200 head Death loss due to SIV 2% Pig value \$100.00 Death loss cost/pig \$2.00 Treatment costs/pig if SIV outbreak occurs \$1.00 Missed opportunity weight gain due to SIV 8.0 lb. Value per pound \$0.45 Cost of lost weight gain/pig \$3.60 Total loss due to SIV/pig \$6.60 Occurrence rate 33% Average loss/pig \$2.20 Reduction in losses due to vaccination 75% Value of vaccine \$1.65 Cost of vaccine and administration \$0.80 Return ratio on vaccine investment 2.06 1Calculations: 2% × \$100 = \$2.00 \$1.00 × 8 lb. × \$0.45 = \$3.60 \$2.00 + \$1.00 + \$3.60 = \$6.60, × 33% = \$2.20 × 75 = \$1.65 ÷ \$0.80 = \$2.06.

When evaluating respiratory disease, use the most cost-effective way to identify the infectious agents involved. Diagnostic tests utilizing serum, nasal swabs and lung tissue are essential to an accurate diagnosis and SIV prevention strategy.

Cost Factors

Once SIV has been confirmed, decisions must be made regarding the cost, prevention and control of disease caused by this virus. Usually, some other viral or bacterial agents are also involved in grow-finish pigs.

Although no exact method is available to determine exact losses, Table 1 demonstrates one way to assess losses. For example, if one out of three of a producer's finisher barns are clinically affected (33.3%) by SIV, and death loss has increased by 2%, 8 lb. less weight per pig sold and \$1/pig medication cost, the average overall loss in the three barns is about \$2.20/pig finished on the site.

To determine whether vaccination for SIV is cost effective, look at whether vaccination can lower losses, the cost of the vaccine and the desired return on investment.

For example, assume a 75% reduction of the listed losses by vaccinating at a cost of 80¢/dose total administered, and a required return of 2:1 to justify this additional procedure. This example shows a payback greater than 2:1 and would justify the use of an SIV vaccine on this production site.

There are great variations in losses from SIV and geographic distribution of the disease. Therefore, alternative treatment strategies may be considered. Water medications and injectable antibiotics may aid in controlling secondary bacterial pneumonia, but do very little to alter the course of the disease.

Vaccination Timing, Efficacy

Once a decision is made to vaccinate, evaluate optimum timing.

For sow herds, a preferred method is to vaccinate gilts twice, prebreeding, and the sows either quarterly or three weeks before farrowing. If the vaccine doesn't cause any serious side effects, like off feed or abortions, either approach is satisfactory.

Monitoring titers of females of different parities after vaccination assists in determining subsequent boosters. Quarterly whole herd boosters would create varying piglet titers due to variation of sow titers and the maternal antibodies passed to the pigs.

Prefarrow boosters would create less variation in piglet titers and provide high levels of protection to piglets in the nursery. However, this often prolongs maternal antibodies in the pigs and delays effective vaccination of piglets until 12-16 weeks of age.

In piglets, maternally derived antibodies (MDA) must be considered. If pigs originate from a sow herd that has high antibody levels to SIV from either vaccination and/or exposure to natural infection, it is best to delay vaccination until pigs are 12-16 weeks of age to avoid MDA interference.

A shortcut commonly seen in SIV control programs is the temptation to vaccinate once, rather than twice, 2-4 weeks apart, as recommended. Experience and serological testing confirms this single-dose strategy yields unsatisfactory results.

Evaluating vaccine efficacy is very difficult, especially when clinical signs are absent. We ask ourselves, was the vaccine effective or was challenge very low?

Regional comparisons are often used. If neighboring finishers are severely affected with no vaccine history, and vaccinated finishers consistently have closeout data showing superior performance on mortality, morbidity, improved feed efficiency and average daily gain, it is reasonable to conclude that a certain degree of efficacy was achieved.

With properly timed vaccinations, it is realistic to expect reduced coughing, lower death loss and fewer treatments.

While SIV is frequently not considered a major player in the Porcine Respiratory Disease Complex, it has been a very significant economic component in northwest Iowa hogs.

Whether preventative measures are appropriate depends on severity of disease, regional risk of disease, cost of prevention and efficacy of the vaccine. All these factors must be considered in setting SIV control strategies.