Sow herd immunities are very important, not only to protect the sow and gilt from disease flare-ups, but also to provide colostral protection to the newborn piglets at birth.

In the past, more emphasis has been placed on building immunities for colostral protection for the newborn.

But in the last two years, we have found with PRRS (Porcine Reproductive and Respiratory Syndrome) and other viral diseases that protection of not only the parent herd but also new entrants into the sow herd are very important.

Thus, developing gilt immunity is critical to building whole herd immunity.

Remember, try to control gilt infections, either through mild, natural exposure or active immunization. With adequate immunity, the gilt can be added to the herd without breaking with disease. When gilts break with disease, they potentially create widespread disease in the older sow herd.

Case Study No. 1 Gilts were blood tested before a producer brought them into his herd. They were negative for PRRS, Actinobacillus pleuropneumonia (APP), Mycoplasmal pneumonia and swine influenza virus (SIV). They were very clean.

Since the home herd was positive for the above, we decided it was important to acclimate the animals to the diseases through immunizations while they were in isolation. All gilts were given two injections for APP, PRRS, mycoplasma and SIV.

When the gilts were introduced 60 days after arrival, two weeks after the second vaccine injection, respiratory problems quieted down for 10 days.

After 10 days, 20% of the gilt additions broke with pneumonia. Two gilts died and when postmortems were done, lesions as well as a positive bacterin culture were noted.

Animals were then injected with Excenel (broad-spectrum respiratory antibiotic) to which they were sensitive. Animals in the immediate areas, whether sows or gilts, were injected with the antibiotic.

New gilts were immunized two more times with an APP vaccine. Pulmotil (a respiratory feed medication) was used. The death loss stopped in the gilts. If the gilts had not been vaccinated with the APP vaccine, I feel death loss would have been more severe.

Case Study No. 2 Gilts were brought into a depopulated swine unit to improve health, carcass quality and the concept of parent stock. Animals were bled prior to arrival and were found to be PRRS, APP and mycoplasma negative. There were very low titers present for SIV.

Management was pleased with the results of the bleedings for the respiratory pathogens, and decided not to vaccinate gilts for anything other than leptospirosis, parvovirus and erysipelas.

Since the unit was depopulated, cleaned, and disinfected, we felt the odds of having a problem with PRRS, APP, mycoplasma and SIV were very slim.

Animals were introduced into the unit and readied for breeding by feeding to top condition. Breeding was started and carried out for eight weeks without problems.

At the 9- to 10-week period after breeding started, a few animals went off feed with a slight cough. We injected them with penicillin and observed them closely. The antibiotic injections did not alter the course of the infections. The morbidity rate continued to increase with approximately 30-40 animals now being affected. The animals were lethargic and coughing. We took blood samples and checked them for PRRS, APP, mycoplasma and SIV again. Animals were negative for PRRS, APP and mycoplasma, but SIV titers were starting to climb.

There were 240-300 animals bred by this time. Over the next two weeks, animals continued to go off feed at a slower rate. We observed 60-80 abortions.

We boosted the herd again with the SIV vaccine. The herd then began to recover without effect.

Obviously, if we had to do it over again, knowing what we know now, we would have immunized the incoming gilts with the SIV vaccine. We underestimated the SIV or "flu" titers. As a result of this farm and others, we are more routinely immunizing new replacements with the SIV vaccine. We're doing this to not only prevent a break within gilts, but also to protect new gilts from older, exposed sows.

Summary Building sow herd immunity is very important. The goal with controlled exposure and/or immunization is to stabilize the immunities within the herd as well as its new additions. We want to prevent flare-ups within sow herds and within replacements entering herds.

If negative animals flare up and become acutely infected, then they can cause diseases such as PRRS to override immunity in older sows because there is more virus present than antibody in the sows.

Moreover, we must build stable herds that can withstand challenges, as opposed to developing totally negative herds.

The probability of having a herd go negative to APP or mycoplasma is extremely small. So producers need to protect the herd.