All-in, all-out (AIAO) pig flow has always been stressed as a “solution” to swine health problems. This management technique was first used to control diarrhea problems in farrowing.

Because of effective vaccines and other control strategies for neonatal diarrhea, and dramatic changes in the nature of the swine industry, AIAO pig flow for wean-to-finish age groups garners more attention today.

The potential improvement in performance seen in controlled trials is one of the factors encouraging AIAO flow and multi-site production. But as with any technology, field application is seldom as “pure” as the controlled experiments.

On the farm, these two techniques present unique health issues to be addressed, as outlined below.

Case Study No. 1

Several thousand weaned pigs were moved to an empty wean-to-finish site. These pigs were from several sow sites with varying porcine reproductive and respiratory syndrome (PRRS) status. The site was double-stocked with plans to move out pigs as feeder pigs. Site fill time was about three weeks. All pigs were on a two-dose Mycoplasmal pneumonia vaccination protocol.

Within three weeks, there was a significant amount of coughing and thumping in these pigs; the clinical diagnosis was swine influenza virus (SIV). Four to five weeks later, respiratory problems increased. Numerous pigs were thumping and coughing and several had mild purple discoloration (cyanosis) of ears and/or some splotchy purple skin patches. Gross lesions were consistent with a “meaty” lung typical of interstitial pneumonia. Several pigs had infection on the surface of the heart and lungs typical of Haemophilus parasuis.

Pigs responded poorly to antibiotics and several became pale, poor-doers. Samples were collected on pigs 11 to 14 weeks old. Samples were positive by immunohistochemistry (IHC) for PRRS and porcine circovirus. Microscopic lesions seen with postweaning multisystemic wasting syndrome (PMWS) weren't found. Some of the lungs submitted did have bacterial pneumonia lesions. Mortality and culls were very high for this “fill.”

After emptying the site, it was cleaned, disinfected and refilled. Changes made included sourcing the PRRS-positive pigs from one sow herd and the PRRS-negative pigs from other sow herds, all housed together in four barns.

Besides mycoplasma, this group was also vaccinated for Haemophilus parasuis. Although a lung sample was IHC positive for SIV when pigs were 9 weeks of age, overall respiratory status improved significantly.

Interestingly, at 9-10 weeks of age, 10 of 10 pigs tested in the PRRS-negative barns were still PRRS negative by enzyme-linked immunosorbent assay (ELISA). Six of 15 pigs sourced from the PRRS-positive farm were ELISA positive at 8-11 weeks of age.

Although these groups have not been closed out, mortality from wean-to-market is projected to be less than 5%.

Case Study No. 2

This nursery is run continuous flow, but rooms are cleaned and disinfected between groups. Feeder pigs are moved to contract growers at 45-60 lb. Nursery mortality has recently stayed below 2.5%.

Pigs were weaned at 17-20 days of age from a 2,500-sow herd into an off-site nursery. Some swollen joints or nervous signs common with Streptococcus suis infections were observed in the nursery. One pig was found to have Strep suis Type 2. Only PRRS was isolated from the serum of a second pig observed the same day showing mild cyanosis of the ears.

A shipment of 600 pigs from this nursery site was delivered during one of Indiana's big July rains. A week to 10 days later, pigs began to die. Within two days, death loss was already 2.6%. The barn that did not get stressed lost only one pig.

Clinical examination found pigs were depressed, lying down and showing high rectal temperatures. Brain and liver cultures of a pig that died revealed pure cultures of Strep suis Type 2. Samples were not checked for PRRS, but based on recent results at the source, PRRS could have been another factor. Also, the death loss accelerated the day after the group was vaccinated for mycoplasma.

Treatment of individual pigs with high doses of antibiotics plus corticosteroids and water medication using sulfadimethoxine stopped the death loss.


These case summaries demonstrate that AIAO pig flow doesn't always work perfectly, whether the AIAO is by room or by site. Certainly, large populations of pigs at sites present an increasing need to understand the patterns of disease agents.

The second case study demonstrates how essentially the same pig population may react differently, based on complicating factors.

To reduce the impact of disease, practitioners and producers must learn to “adjust the flow,” rather than always “go with the flow” in multi-site production systems.