Streptococcus suis infection can cause systemic disease in all ages of pigs with clinical signs ranging from septicemia to central nervous system symptoms. It is a common problem worldwide and responsible for major economic losses to the industry. So far, there are no efficient alternatives to antibiotics in controlling S. suis infection and it’s one of the main reasons for antibiotic use in pig farms. Therefore, it would be important to find non-antibiotic solutions to inhibit the infection and its negative consequences.

The upper respiratory tract is believed to be the primary transmission route of S. suis and the gastro-intestinal tract the secondary one. To be able to cause clinical infection S. suis has first to adhere and colonize in the animal and then to translocate through epithelial barrier, spread in connective tissues, lymphatic system and blood stream and to infect different organs. After being transmitted nasally or orally, S. suis can colonize the palatine tonsils of pigs. Resin acids are well known for their antimicrobial and anti-inflammatory properties. The antibacterial activity of resin acids against Gram-positive bacteria, such as Streptococcus suis, is likely related to solubilization of the bacterial cell wall or altered cell membrane proton gradients. Resin acids have also been shown to strengthen the intestinal epithelial barrier by preventing the inflammation induced enzymatic degradation of the connective tissues and tight junction proteins. The resin acids thus have a potential to reduce bacterial translocation. These properties made the resin acids of Progres® an interesting product to test in S. suis challenged piglets.

Materials and methods

The present study aimed at testing the effect of Progres® to reduce the colonization of S. suis serotype 9 (SS9) in weaned piglets after SS9 challenge. The trial was conducted at Schothorst Feed Research, The Netherlands as a part of a larger study. In the beginning of the trial, 15 female and 15 male piglets were randomized into 6 pens and 3 treatments: non-challenged with control diet (NCC), challenged with control diet (CC) and challenged with Progres® addition in the diet. All piglets received an adaptation diet during the first week after weaning (Figure 1).

Figure 1. Design of the Streptococcus suis challenge trial

On day 11 of the experimental period, piglets in NC and Progres® treatments were inoculated with SS9 (isolate 2524) via oral and nasal routes with 3 mL at the dose of 1.0 x 108 CFU/mL per route. Piglets in the NCC treatment received phosphate saline buffer (PBS) via the oral and nasal routes.

On days 12, 13, 15, and 19, tonsil swabs were collected from all of the piglets. Health status and mortality of piglets were checked on daily basis. Rectal temperatures were measured at frequent intervals during the study. At the end of the experiment piglets were weighed and then euthanized to collect ileal digesta samples. The DNA was isolated from tonsil swabs and ileal digesta and the samples were analyzed for SS9 by using quantitative PCR analysis.


Fever related to the clinical signs of S. suis infection was not observed in any of the treatments. The ileal quantity of S. suis (SS9) was similar in all treatments (2.9, 2.0, 2.9 log10 CFU for NCC, CC and Progres®, respectively. The fact that also the nonchallenged animals presented high ileal S. suis counts suggests a high background challenge in this trial.
Before the challenge, the quantity of SS9 in the tonsil swabs was also similar in all treatments. For the combined data after the challenge, the quantity of SS9 was greatest in the challenged control, Progres® being the intermediate and the non-challenged control the lowest (Figure 2). The results indicate that dietary Progres® at 1 kg/ton may reduce Streptococcus suis (SS9) colonization in piglet tonsils.

Figure 2. Colonization of S. suis (SS9) in the tonsil swabs of piglets after the challenge (days 12–19)


The present experiment studied the effect of Progres® on the quantity of Streptococcus suis in the ileum and tonsils of piglets. The results suggest that Progres® can reduce the quantity of S. suis in the tonsils, which act as its reservoir in piglets. Therefore, Progres® is suited for reducing the S. suis disease pressure in piglet farms.