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

Abstract Background: Streptococcus suis (S. suis) infections are responsible for a large disease burden in piglets after weaning, compromising animal welfare and increasing antibiotic use. The immune gap caused by decreased maternal-derived antibodies (MDA) and insufficient acquired antibodies in weaned pigs could be a key factor for 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 until10 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 hours 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. suisserotype 9 before weaning, while the prevalence of serotype 2 increased after weaning. Conclusions: The lowest level of S. suis-specific antibodies was detected just before weaning, which contributes to piglet susceptibility to S. suis infections. Farmers and veterinarians should focus on piglets with low birth weights, late-born piglets, and/or piglets with low colostrum intake because these parameters reduce both the S. suis-specific MDA preweaning and the specific antibodies acquired postweaning.