How Long Does Maternal Immunity Last in Rabbits?

In this second episode, Massimiliano Baratelli explains how maternal immunity is transmitted to rabbit kits and how long it lasts. Based on the study “Characterization of the Maternally Derived Antibody Immunity against Rhdv-2 after Administration in Breeding Does of an Inactivated Vaccine”, he describes how vaccinated breeding does pass strong passive protection to their offspring—mainly through the placenta—and how this immunity gradually decreases, disappearing in all young rabbits at 58 days of age. 

These findings help determine the right timing for primo-vaccination and highlight the importance of vaccinating breeding does well before parturition.

Transmission of IgG in Rabbits 

The transmission of antibodies (specifically IgG) depends on three main pillars that determine whether a newborn is born protected or relies entirely on colostrum: 

1. Placental Barrier (Physical Structure): the most critical factor is the number of tissue layers separating maternal and fetal blood.
2. The Neonatal Fc Receptor (FcRn): these receptors bind specifically to the Fc portion of the IgG molecule, protecting it from degradation while transporting it across the cellular barrier into the fetal circulation. IgG has the specific structure required to bind to the FcRn receptor.
3. The "Open Gut" Window (Postnatal Transfer): in species with low or no placental transfer, antibody transmission depends on how long the intestinal cells of the newborn can absorb antibody molecules.

Rabbits have a hemochorial placenta, therefore maternal antibodies are mainly transmitted from the mother to the offspring through the placenta, as demonstrated in this study. Although a small quantity of IgG was detected during lactation, gestation was the most important route, with the highest amount of maternally derived antibodies (MDA) transferred to the rabbit kits. 

In the following table, there is a comparison between different species. Human and rabbits share a similar type of placenta, which means that the main route of IgG transfer occurs during gestation. In contrast, in cats and dog the main route is colostrum, as the endotheliochorial placenta does not allow this effective transfer of IgG antibodies.

In the case of colostrum, IgG transfer in rabbits and humans is low. However, in dogs and cats it represents the primary route of passive immunity, making it essential for adequate protection in newborn animals. 

Duration of maternal immunity against RHDV2 

While the presence of antibodies at birth is important, it is equally critical to understand how long these maternal antibodies remain in rabbit kits. 

The study discussed during the interview monitored antibody levels in rabbit kits over time and found that maternal antibodies persisted for at least 28 days after birth. During this first month of life, all rabbit kits maintained detectable levels of maternal antibodies, providing a window of passive protection against rabbit haemorrhagic disease. 

However, these antibody levels gradually declined as the kits grew. This decrease is a natural process, as maternal antibodies are not produced by the young animal and eventually disappear as they are metabolized. 

By 58 days of age, none of the animals in the study retained detectable maternal antibodies. At this point, the rabbits were no longer benefiting from passive immunity and relied entirely on their own immune system for protection. 

Implications for Vaccination Strategies 

The findings provide valuable guidance for the development of effective vaccination protocols in rabbit.

First, they confirmed that vaccinating breeding does is a key strategy for protecting newborn kits during the earliest stages of life. Maternal antibodies act as a protective shield while the kits’ immune systems are still developing. Second, the study demonstrates that the immune response generated in breeding does is long-lasting, allowing them to transmit antibodies to their offspring even up to one year after vaccination. 

This means that, under normal circumstances, annual vaccination of the mothers is enough to maintain passive protection in their offspring. Therefore, there is no need to re-vaccinate the mother every time she breeds. 

Finally, understanding the decline of maternal antibodies helps determine the most appropriate moment to vaccinate young rabbits, minimizing the risk of interference with maternal antibodies while ensuring that animals are protected before they become susceptible to infection.