Levels of Circulating IgM and IgY Natural Antibodies in Broiler Chicks: Association with Genotype and Farming Systems

SIMPLE SUMMARY: Poultry is currently the most efficient animal productive system and could contribute to fulfilling the need for protein in order to supply the increasing human population. However, intensive selection of broilers makes them more susceptible to several welfare concerns. Moreover, in order to improve animal welfare, alternative housing systems, such as free-range and organic systems, are becoming increasingly popular. These changes in the modern poultry industry, in combination with restrictions on antibiotics, have led to the need for poultry with higher disease resistance. Naturally occurring antibodies (NAbs), which are major components of innate immunity, have been previously detected in chicken sera. These studies showed that NAbs are heritable and that high levels of NAbs are associated with survival and highly specific antibody responses against pathogens. Therefore, we investigated the circulating levels of IgM and IgY NAbs against selected antigens (actin, DNA, trinitrophenol and lipopolysaccharide) as potential biomarkers of poultry welfare and productivity in fast-growth (Ross 308) and slow-growth (Sasso) broilers raised in conventional and free-range systems, respectively, under 3-year industrial-scale production. Overall, we demonstrated significant differences in IgM NAb levels during the final breeding step between the two commercial genotypes, highlighting NAbs as potential biomarkers to be exploited in the poultry industry. ABSTRACT: Naturally occurring antibodies (NAbs), which are major components of innate immunity, exist in circulation under healthy conditions without prior antigenic stimulation and are able to recognize both self- and non-self-constituents. The present study aimed at identifying potential immunological differences between commercial fast- and slow-growth broilers (n = 555) raised in conventional and free-range systems, respectively, through the use of the specificity, isotypes and levels of circulating NAbs. The possible beneficial effect of oregano-based dietary supplementation was also evaluated. To this end, serum IgM and IgY NAbs against self- (actin and DNA) and non-self- antigens (trinitrophenol and lipopolysaccharide) were measured by ELISA and further correlated with genotype, season and performance. Significantly higher levels of IgM NAbs against all antigens were found in slow-growth compared to fast-growth broilers. IgM NAb levels were also significantly increased in dietarily supplemented slow-growth broilers versus those consuming standard feed. Moreover, significantly elevated levels of anti-DNA IgY NAbs were found in fast-growth compared to slow-growth broilers, whereas the opposite was observed for anti-LPS IgY NAbs. Multivariate linear regression analysis confirmed multiple interactions between NAb levels, genotype, season and performance. Overall, serum NAbs have proven to be valuable innovative immunotools in the poultry industry, efficiently differentiating fast-growing versus slow-growing broilers, and dietary supplementation of plant extracts can enhance natural immunity.