Insufficient protection of piglets against S. suis infections through maternal immunity

In pig farming, the weaning dip is a well-known phenomenon. It is a vulnerable period in the life of a growing piglet, the moment when piglets are taken out of the farrowing pen and have to continue independently. Over the past four years, a consortium consisting of ForFarmers, Trouw Nutrition, Boehringer Ingelheim and Wageningen Bioveterinary Research (WBVR, part of Wageningen University & Research) has investigated how immunity to Streptococcus suis (S. suis) progresses in the weeks from piglet birth until three weeks after weaning. For this research, field studies were carried out at various pig farms in the Netherlands. On these farms, the immunity transfer from sow to piglet and the build-up of the piglet's own immunity were examined. The results were recently presented during a closure meeting of the project Piglets in Transition – Possibilities for Approach (BITMAP).

Birth order

The sow transfers antibodies (Immunoglobulin, Ig) to her offspring via the colostrum. “The composition of the colostrum is determined in the last weeks of the pregnancy. Therefore, the amount and constitution of the colostrum have already been determined before farrowing begins,” says Jan Fledderus of ForFarmers. “As a result of hormonal changes, the colostrum will be ‘diluted’ with milk from the moment farrowing starts. This means that proportionally firstborn piglets receive more antibodies than lastborn piglets.” Fledderus points out that birth order is a determining factor, not birth weight. “Firstborn piglets can get colostrum earlier and that colostrum is of better quality. We see this in all trials.”

Maternal immunity

To gain more insight in maternal immunity, the presence of antibodies was examined in colostrum as well as in the blood of the sow and piglet. “We find high levels of Ig antibodies in the colostrum in the first 24 hours after birth, but the composition of the colostrum changes rapidly during that period,” says WBVR researcher Sandra Vreman. Antibodies were also abundant in the blood of sow and newborn piglets (after colostrum intake). “After birth, the amount of antibodies in the piglet's blood decreases. Around day 18 to 23 after birth, just before weaning, that level reaches its lowest level. If the piglets are weaned during or shortly after this period, this low level of antibodies can be an important contribution to the well-known weaning dip.”

Specific immunity

To detect these specific antibodies, a special ELISA test was developed at WBVR, which makes antibodies of S. suis type 2 and 9 visible. “Based on these findings, the question is whether piglets have the right type of antibodies in the vulnerable period of their lives.”

Vreman points out that the majority of sows caries S. suis. The highest concentrations of the bacteria are detected in the saliva, genitalia and tonsils. As a results piglets can be colonised with S. suis as early as during birth. “This underlines the great importance of colostrum intake from the piglet's own mother. It is likely that the colostrum of the mother contains the antibodies that match the mother's microbiome. This colostrum will therefore offer the piglets the best possible protection against any germs present in this phase.” According to Jan Fledderus of ForFarmers it is also striking that sows with a high specific defense against S. suis pass this on to their piglets. “This aspect should be further explored in a future study.”

Minimise mixing

Much knowledge has been gathered on S. suis pathogenesis (the disease course) for the past decades, but there is a lack of knowledge on the very first steps of the diseases and the trigger factors, says Lluís Fabà of Trouw Nutrition. “From our internal research and research in this consortium, it seems clear that some sows and some litters are more likely to have pigs with S. suis infections than others. Fabà speaks of a 'sibling effect'. “Therefore, a practical advice is to minimise the mixing of piglets and maintain the litter group together during the streptococcal disease susceptible phase to reduce the risk of spreading the disease through a barn,” says Fabà.

Rutger Jansen of Boehringer Ingelheim endorses Fabà's findings. “We have also seen that keeping a litter together ensures that any pathogens present remain within the control.” Another relevant observation in the field trials was that piglets that have a low colostrum intake at the start are still vulnerable even after weaning. “By not mixing litters and ensuring good colostrum intake, pig farmers can contribute to a robust start to the rearing period,” says Jansen.

Shifting weaning moment

Jan Fledderus of ForFarmers points out that sows differ from each other when it comes to their mothering skills. “Our observations show that one sow suffers more loss of condition after farrowing than the other. The sow with more condition loss produces piglets with more weight gain in the farrowing pen," says Fledderus.

Because of the differences per sow, Fledderus advises in particular to inseminate gilts a little earlier. “Weaning is usually done at a set date, but farrowing in a barn is spread over several days. This ultimately leads to an age difference of three or four days between piglets at the time of weaning. The effect of that age difference on the quality of the piglets can be reduced by specifically inseminating gilts in the group earlier, so that their piglets are slightly older at the time of weaning.” Ultimately, according to Fledderus, it is desirable to shift the weaning moment to an older age of the piglets if this fits into the farm management. “The percentage of problem piglets will decrease and due to a higher weaning age, the buildup of antibodies will have improved drastically. Every extra day the piglet remains with the sow provides immediate benefits in rearing,” concludes Fledderus.