The kinetics of maternal and self-developed Streptococcus suis-specific antibodies.

Background: Streptococcus suis (S. suis) infections are responsible for a large disease burden in piglets during the nursery phase, compromising animal welfare and increasing antibiotic use. The immune gap caused by decreased maternal-derived antibodies (MDA) and insufficient levels or functionality of acquired antibodies in weaned pigs could play a role in the increased susceptibility to S. suis infections. To better understand this, two studies were performed. Study I evaluated the associations between sow antibodies in colostrum and serum, birth parameters (e.g., birth weight, colostrum intake and piglet growth) and the levels of S. suis-specific (serotypes 2 and 9) antibodies in one-day-old piglets from four farms. Subsequently, study II used one of these farms to evaluate S. suis-specific and total antibody kinetics in piglets (10 litters with 6 selected piglets per litter, total n = 60) from birth until 10 weeks of age. Additionally, tonsil swabs from sows and piglets were taken to evaluate the S. suis tonsillar carrier status (serotypes 2 and 9) before and after weaning.

Results: High variability in serum and colostrum antibody levels was observed between and within the four farms (study I). In study II, there was a decrease in S. suis-specific MDA after 24 h of age, with the lowest level occurring at approximately 18/19 days of age. Afterwards, there was an increase in specific antibodies, most likely due to acquired immunity. Colostrum intake, birth weight and 24-h weight gain after birth were important parameters that were positively associated with S. suis antibody levels in piglets after birth but also affected these antibody levels at a later age. All the piglet tonsils were colonized with S. suis serotype 9 before weaning, while the prevalence of serotype 2 increased after weaning.

Conclusions: Total Ig against S. suis in serum declined after birth and the lowest level was detected just before weaning. Farmers and veterinarians should focus on piglets with low birth weights and late-born piglets because these parameters reduce both the S. suis-specific MDA preweaning and the specific antibodies acquired postweaning. Colostrum intake and 24 h-weight gain also affect the level of S. suis specific antibodies on day 1.