Understanding immunity against Streptococcus suis infections in young piglets

Streptococcal (S.suis) infections in pigs are responsible for a large disease burden in piglets after weaning, making them the most common reason for antibiotic use in pigs. The disease is also a major economic loss for the pig sector. In the four-year project Piglets in Transition, Possibilities for tackling Problems (BITMAP) ForFarmers, Trouw Nutrition, Boehringer Ingelheim and Wageningen Bioveterinary Research (WBVR, part of Wageningen University & Research) are working together to improve the resilience of piglets to this bacterial disease.

Defences and antibodies

Antibodies play an important role in the defense against S.suis infections. In the BITMAP project, antibodies have been determined in the blood and colostrum of the sow. “We looked at both general antibodies and antibodies specifically directed against S.suis”, explains WBVR researcher Sandra Vreman.

The course of antibody concentrations in the piglet blood from birth to 3 weeks after weaning was also analysed. In addition, this research group measured functional parameters around birth, such as birth weight, birth order, colostrum intake, growth and nutritional intake. “This information gives us insights into the critical periods for piglets, where infection with S.suis may occur.”

Dip in defences around weaning

Piglets are especially vulnerable during weaning. Data from the first field study show that, just after birth, the piglets have a good antibody concentration in their blood. This is due to the fact that the piglets receive ample amounts of antibodies from the sow (maternal antibodies) through the colostrum. However, the antibody concentration decreases over time and just before weaning, the level of these antibodies is at its lowest. The maternal antibodies obtained through the colostrum are, therefore, not protective against S.suis infections around weaning and during piglet rearing.

Colostrum uptake and birth order

A field study makes clear that various factors surrounding birth may influence the general antibody concentrations and the levels of S. suis specific antibodies in the blood over time. In particular, colostrum uptake and birth order are important for the antibody concentration immediately after birth, but these factors can also influence body weight around weaning. A S.suis outbreak also revealed that physiological parameters (e.g. weaning weight, colostrum uptake, birth order and amount of specific antibodies in blood piglet) did not affect S.suis infection after weaning in this field study. However, there are indications that piglets from the same litter were infected and that a genetic factor may also play a role.

From data to practice

By registering the birth process, earmarking the new-born piglets and keeping the weaned piglets together per flock in the piglet rearing, a unique dataset was obtained in this project. This database is of great importance for follow-up research into the build-up of immunity and how it can be influenced.

The research shows, among other things, that colostrum intake and birth order of piglets influence the concentrations of both general and specific antibodies in the blood of piglets. The S.suis specific maternal antibodies decrease after birth and are very low around weaning. Therefore, piglets around and after weaning may not be sufficiently protected against this infection. The effect of sow vaccination to protect the piglets against S.suis infections around weaning may, therefore, be limited. “The great added value of this project for practice is linking scientific knowledge and insights to daily practice in pig farming,” says Jan Fledderus of ForFarmers.