In most farrowing operations, the number of pigs weaned per litter is impacted more by preweaning mortality than by the number of pigs born alive.

Significant increases in pigs/sow/year (p/s/y) can be gained by maximizing piglet health and minimizing preweaning mortality. The greatest percentage of preweaning mortality occurs within the first three days after farrowing. To optimize health during this period, preparation must begin well before farrowing.

Piglet health status is the balance of immunity and disease challenge. A high level of immunity in a clean environment is most likely to produce healthy pigs. Both of these activities originate with the sow well before farrowing.

Building Pig Immunity

Piglet immunity has two critical mechanisms, generally referred to as “acquired” and “innate.”

Acquired immunity is the focused response to specific disease organisms. Included in acquired immunity are antibodies that are produced by the sow and transferred to the pig via colostrums (first milk).

Innate immunity consists of general barriers to infection, such as moist mucus membranes to filter inhaled pathogens, and normal intestinal bacteria that compete with potential pathogens for food.

Acquired immunity is very specific and efficient, but slow to develop at the first exposure to disease. Innate immunity is less efficient and specific, but generally operates all of the time.

Improving innate immunity depends on proper environmental conditions, such as temperature and humidity, and adequate nutrition for the piglet (See sow and pig nutrition, page 34).

Piglets are born with the ability to use both types of immunity. However, because acquired immunity may take 7-14 days to peak after exposure to a disease, piglets are provided premade antibodies by the sow via colostrums. Figure 1 illustrates the general process of immune system events that have to culminate at farrowing for early protection. The relative timing and quality of each step affects the final concentration of antibodies that the piglet receives.

For example, if vaccination occurs at mid-gestation rather than at late gestation, sow antibody levels will have peaked and be declining when it is time to concentrate them in the colostrum for presentation to the pigs.

Likewise, if gilts do not receive at least two doses of vaccine at least two weeks apart prior to farrowing, the level of antibodies in the colostrum will be greatly reduced.

Similarly, if poor injection technique or vaccine handling means that the sow receives less than the entire dose of a quality vaccine, the level of antibodies available to the piglets in the colostrum will be reduced.

Poor nutritional status of the sow might reduce the energy available for building antibodies, again resulting in lower levels in the colostrum.

From the piglets' standpoint, a poor microenvironment might prevent them from nursing adequately, and soon enough after farrowing, to get maximum antibodies from the colostrum.

Timing is Everything

A recent case study illustrates the importance of timing. A farrow-to-wean farm was experiencing scours with increased preweaning mortality. Diagnostic testing identified the pathogen causing the problem as an Escherichia coli (E. coli) strain that was included in the pre-farrow vaccine. The vaccine specified that sows receive the vaccine three weeks (21 days) before farrowing. However, the farm vaccination protocol was to administer sometime in the “third week” before farrowing, as work flow allowed.

Figure 2 illustrates the real difference in timing of vaccination — although they appear to be similar.

To maintain work schedule flexibility, injections were moved to the fourth week, pre-farrowing, so that there was at least 21 days between vaccination and farrowing.

Additionally, the farm was in the habit of warming the vaccine prior to injection. This is unnecessary and may contribute to the breakdown of the vaccine. When these two problems were corrected, the piglet scours resolved.

An effective pre-farrowing sow and gilt vaccination program that is diligently maintained is a basic requirement. This case demonstrates that there are three crucial considerations: 1) selection of the correct vaccine, 2) correct administration technique, and 3) correct timing.

A number of products are available on the market for vaccinating sows and gilts prior to farrowing in order to boost maternal antibodies by the time of farrowing. Selecting the appropriate product requires veterinary interpretation of diagnostic testing in affected piglets. There are many organisms, such as E. coli, that have non-pathogenic and disease-causing strains. Molecular testing can determine which vaccine is appropriate.

Effective vaccines do not exist for all potential piglet pathogens. Other techniques to immunize sows prior to farrowing include fecal feedback, autogenous vaccines and controlled exposure to wild-type pathogens.

However all of these approaches have potentially serious side effects for the herd, so plans should be developed with input from a veterinarian who is thoroughly familiar with your herd and its health status.