While early weaning carries many advantages, long-term this management option serves up some new challenges.

The push for high health and least-cost pork production includes various forms of medicated early weaning (MEW), multi-site production and gilt replacement plans.

High health can be a relative term. For instance, high-health, MEW farms commonly break with so-called "suis-cide" diseases (Streptococcus suis, Actinobacillus suis and Hemophilus parasuis), challenging today's hog veterinarians.

MEW to Save the Day The fact is, most breeding herds carry the majority of the significant hog disease pathogens. That's where MEW enters the picture.

The underlying premise of MEW is that "clean" pigs can be weaned and reared disease-free from a "dirty" sow herd if the following conditions occur:

- The sow herd has an immunity through natural and/or vaccine exposure to the pathogens that are present on that breeding herd farm;

- This immunity is transmitted through the colostrum to the piglets resulting in the piglets being protected from infection passively from the sow;

- This passive protection decreases over time. If the piglets can be weaned before the passive protection decreases to a level that is no longer protective for the disease, the pigs can be weaned "free" of the pathogens present in the sow herd; and,

- If these "clean" pigs can be reared away from the "dirty" sow herd, the pigs can remain disease-free all the way to market.

While MEW has been proven to work in herds, the long-term application to modern production systems often experiences these four potential shortcomings:

1. Sow herd immunity: All females in the herd don't have the same level of immunity. This is due to parity effects (gilts and older sows), inadequate acclimation procedures and subpopulation effects of diseases such as porcine reproductive and respiratory syndrome (PRRS).

Sub-populations are segments of the group that remain naive while penmates are protected from infection. These naive pigs can cause disease outbreaks and persistent infections.

Sow health can be compromised. The sow herd sometimes develops acute infections that can be transmitted to offspring before those sows generate an immunity to protect the piglets.

Consequently, a percentage of the pigs weaned don't carry the level of immunity needed to protect them from disease. They may become infected and spread pathogens to other early weaned pigs.

2. Passive transfer of sow immunity: Colostral antibody transfer to piglets is usually assumed but seldom investigated. Sandy Amass, DVM, Purdue University, says that fully 12% of piglets are naive; they don't get adequate colostrum on day one.

Protective colostrum may also be deficient in gilt litters when pre-farrowing immunizations are mistimed and when sows don't milk properly.

Not all pigs receive adequate protection even when sows provide it in colostrum. Weak pigs are incapable of nursing to obtain adequate colostrum. Inappropriate fostering can lead to poor colostrum intake.

Variability of passive immunity levels results in some weaned pigs lacking sufficient immunity for disease protection, and these pigs may be weaned with an infection that will be spread to others in the nursery group.

3. Weaning before passive immunity wanes: There is a natural variation in the time it takes for immunity to decline in piglets.

One reason is fostering practices can make accurate age identification of individual piglets difficult. Some pigs are older than you think at weaning.

As before, variation in individual pig immunity and weaning ages produces pigs at risk for infection and disease spread to other weaned pigs.

4. Rearing "clean" pigs away from "dirty" sows to keep pigs disease-free: Disease can be spread from other sources than the vertical (sow-to-pig) transmission.

Lateral (pig-to-pig) transmission from other age groups on the site includes:

- Airborne transmission from area farms;

- Disease carriers such as transport vehicles;

- Disease spread within the group through "carrier" pigs; and,

- Disease pathogens transmitted through inadequate biosecurity.

While it's possible to rear pigs free of sow herd diseases, some groups of pigs may become infected with diseases outside the herd.

Multiple-Site Health Implications Multiple production sites create economic and management issues that can have health implications. The fixed costs of each site, such as the well or back-up electrical systems, encourage producers to place as many pigs on each site as possible to lower fixed costs/pig. The result can be multiple ages of pigs on sites or in buildings, increasing potential lateral spread of infection.

To keep all-in, all-out (AIAO) pig flow with high volumes of pigs on different sites, the temptation is to commingle sow sources on one site. This adds exposure to different pathogen carriers and levels of immunity.

The fixed cost incentives to bend these rules have cost the industry greatly when diseases such as PRRS strikes.

Other MEW health issues include:

- People: Multiple sites are often managed by staff who travel to more than one site. Teamwork can be difficult to achieve. Management variation makes treatments inconsistent across sites and even days of the week. Farms need to adjust teaching methods and recognize that incentives and goals that focus on only one segment of production have risks.

- Biosecurity: Multiple sites can mean many pig movements between sites. This increases the biosecurity risks associated with truck washing and pig movement.

In areas of high pig density, adding sites may just bring neighboring systems closer together, creating new disease concerns.

Site separation has been used with sow herd expansion, spurred by specialized labor and leveraged dollars to build contract production units.

The full potential of multi-site isn't realized, however, when people, equipment and pigs move too freely between farm sites.

- Other issues: Antibiotics are administered to piglets as part of normal baby pig care and strategically for MEW plans. This has been tremendously successful with such diseases as atrophic rhinitis. However, the updating of antibiotic sensitivities must become routine to maintain effectiveness. Sow medication is almost uniformly avoided except post-farrow treatment or for clinical signs of disease.

An estimated 50% annual gilt replacement rate and shoddy breeding stock isolation and acclimation practices don't provide much pig population immunity. K88 E. coli, rotavirus and Clostridium perfringens can all create diarrhea problems in the farrowing barn.

Early age gilt matings often follow incomplete exposure to farm pathogens via natural and/or artificial (vaccine) means.

The new age pathogens such as porcine type II circovirus have been discovered in multiple site production systems.

Many emerging diseases in early weaned systems are actually old pathogens such as Streptococcus suis and Haemophilus parasuis. These organisms can be more severe when a high-health population is weaned early. Large numbers of susceptible nursery pigs can be infected by carrier pigs in the group, resulting in a very impressive disease outbreak.

Critical Control Points The key to optimum early wean pig health is pig flow.

As farms move to strict pig segregation by air space, diseases tend to go away. But, when we break the golden rules of pig flow, pigs, people and profits suffer.

Production technologies that fit into a correct pig flow model are:

- Specialized sites: Multi-site production has proven its merit because of labor, population size, financing, permitting, information and other management advantages. One-site production is still very profitable for many farms, particularly those with high health and excellent financial records.

However, numerous multi-site systems don't take advantage of this separation because they believe off-site, continuous-flow nurseries can work. They don't. At least, not for very long.

Commingling weaned pigs still takes place, even though data teaches us the pitfalls. PRRS and associated respiratory diseases and the enteric diarrhea complex have taught us the dangers of commingling.

- Segregated ages: We are moving way beyond AIAO. Farms are keen to the production advantages of separating populations by age and air space. Through nutrition, environment and immunity, targeted management with little age spread will reduce weight variation.

- Healthy sow herd: Health starts at the breeding herd. Prioritize maintaining a healthy breeding herd with a stabile immune status. Remember that breeding herd pathogens will eventually work into some production groups. Understand your disease profile well enough to prepare gilt introductions properly, and verify that gilt health does match sow herd health.

- McRebel: McRebel stands out among the management techniques most successful in reducing PRRS effects in the farrowing barn and wean-to-market herd. McRebel emphasizes low/no fostering (limits crossfostering to the first few days of a pig's life), forces weaning (no hold-back pigs) and includes the humane elimination of poor-quality pigs from the population at each stage of production. Tough love leads to shorter duration of PRRS production losses and forces a change in the pig flow thought process.

- Wean-to-market: Group integrity and information integrity are being observed on farms that want to operate with knowledge. It can be done with conventional nurseries and finishers or via the wean-to-finish facilities developed over the last several years. Once this forced AIAO is accomplished, truth will surface from your management information system.

- "Hotel" nurseries: These commingled group nurseries don't produce good performance and healthy pigs. Our databases describe routine wean-to-market improvements of 0.1-0.2 lb. in average daily gain and 1-3% in mortality for AIAO systems over "hotel" production.

- Ongoing health monitoring: Prioritize health monitoring, diagnostics and treatments throughout all phases of production. Individual care throughout the life of each pig will improve the entire group's performance. Expect the pathogens to change from group to group, and be prepared to prevent and treat as needed.