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.

The global demand for improvement in the welfare conditions of broilers has generated the necessity to implement alternative rearing systems as well as less intensive growth hybrids. The majority of the data on alternative farming methods, notwithstanding their abundance, are the result of small-scale experiments. The present extended field study examined the effect of two different industrial farming systems on broilers’ antioxidant status, performance, and meat quality, including 13 replicates of each industrial breeding system (intensive conventional; free range) and two different chicken genotypes (fast growth; slow growth). The duration of the study was 51 months, and the total number of broilers was 260.000 for the conventional and 78.000 for the free-range system. The results showed that fast-growth chicks demonstrated a more satisfactory performance (in terms of body weight gain (BWG) and feed conversion ratio (FCR) with p ≤ 0.001), reduced serum lipid oxidation (p ≤ 0.05), and more tender meat. Contrarily, slow-growth chickens presented significantly higher total antioxidant capacity (TAC) in serum and thigh muscle (p ≤ 0.001), significantly lower (p ≤ 0.05) thigh muscle oxidation (in terms of thiobarbituric acid reactive substances, TBARS), increased protein and decreased fat content (p ≤ 0.05), and better smell, taste, color, and texture. In conclusion, the free-range farming system for slow-growth chickens may result in an overall higher nutritional value, sensory score, and serum and thigh muscle antioxidant profile than the conventional farming system for fast-growth broilers. However, fast-growth broilers exhibit better performance and might undergo less stress.

Identifying blood components influenced by rearing systems that serve as biomarkers to distinguish free-range from conventional broilers can improve animal health, welfare, and productivity. The current study aimed to evaluate specific blood parameters related to immune function and tissue stress, as biomarkers to differentiate free-range, slow-growing Sasso broilers from conventionally raised fast-growing Ross 308 broilers. For this purpose, serum IgM Natural Antibodies (NAbs) targeting actin and lipopolysaccharides (LPS) as key immunological parameters of natural immunity, along with creatine phosphokinase (CPK) and other significant stress and tissue-related biochemical parameters, were measured in a total of 300 broilers (150 per group) raised under industrial scale rearing systems, by standard methodology. Our results showed significantly higher IgM-NAb levels to both antigens and lower CPK and Aspartate Aminotransferase levels in Sasso broilers compared to Ross 308 broilers (p < 0.001). Combination of anti-LPS IgM-NAbs and CPK levels, as the most potent biomarker candidates, achieved 90% sensitivity and 84% specificity in distinguishing Ross 308 from Sasso broilers. In conclusion, the combined evaluation of these blood biomarkers can effectively discriminate conventional from free-range broilers analyzed herein, with potent novel applications in the poultry industry making it a promising, cost effective and easy-to-use, diagnostic tool.