Characteristics of maternal antibodies transferred to foals raised through maternal equine rotavirus A vaccination

Equine rotavirus A (ERVA) can cause foal diarrhoea and the most common ERVA genotypes are G3P[12] and G14P[12]. Since the introduction of a monovalent killed G3P[12] vaccine, infection in neonates has decreased. We aimed to determine the dynamics and longevity of maternally derived anti-G3P[12] neutralizing antibodies (NAbs) in foals and what, if any, cross-reactivity exists between maternally derived NAbs against G14P[12]. Serum samples were collected from 50 mare-foal pairs before each vaccination and up to 6 months post-foaling for mares and up to 7 months of age for foals. These samples were then used for virus-neutralization antibody assays with both G3P[12] and G14P[12] viruses. We observed that vaccination of mares could increase their serum NAb titers. Pre-nursing serum samples of foals collected at birth before the first nursing contained no detectable NAbs. In contrast, post-nursing serum samples of foals showed a significant amount of NAb levels, thereby confirming that these NAbs are passed through the mare's colostrum. Our study demonstrated that there is variation in the ratio of NAbs transferred from the serum of mares to the serum of their foals. Results also confirmed evidence of cross-reactivity between maternal antibodies in the serum of G3P[12] vaccinated dams and G14P[12]. Heterologous (G14P[12]) NAb titers were about 2- to 4-fold lower than homologous (G3P[12]) titers in colostrum, milk, and serum samples of both mares and their foals. Our data demonstrate that G3 and G14 NAbs in the serum of foals decreased steadily over time with the lowest point measured at approximately 4 months of age.