Interspecific correlations between oxidative stress status and age-related histomorphometric changes in the bursa of Fabricius of Anas crecca

The Bursa of Fabricius (BF) is a primary immune organ in birds, which is sensitive to infections and external stress. It is responsible for the secretion of proinflammatory cytokines for efficient inflammatory responses; thus, it undergoes significant histomorphological and functional alterations. As oxidative stress plays a crucial role in age-related tissue involution, it is ultimately necessary to understand the relationships between physiological and histological parameters for exploring the correlations between immune organ development and aging processes in the investigated duck species. This study aims to demonstrate correlations between bursal histomorphometric alterations and oxidative stress markers in Anas crecca ducks at two different developmental stages to display age-dependent alterations in BF structure and antioxidant capacity. Twenty Anas crecca ducks were examined at 8 th and 24 th weeks of age (n=10 per group). Histomorphometric analysis included gross bursal measurements (weight, length, and width), and histological parameters (plicae dimensions, muscle thickness, and cortical and medullary thickness) were measured. Oxidative stress markers also measured included antioxidant markers such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and prooxidant markers (lipid peroxidation (LPO)) and nitric oxide (NO). Statistical analysis employed Pearson correlation, chi-square tests, and comparative analysis between two age groups. Significant histomorphometric and oxidative outcomes were observed. The BF architecture in both groups is tightly correlated with the developmental stages and oxidative status. At the 8 th week, ducks exhibited higher antioxidant enzyme activities (SOD: 0.59±0.01 vs 0.34±0.02 U/mg, P<0.01; CAT: 1.94±0.05 vs 1.83±0.09 U/mg, P<0.01) and lower oxidative damage marker (LPO: 4.81±0.11 vs 72.16±1.64 nmol/mg, P<0.01) compared to the 24 th week. Conversely, GPX and NO activities increased significantly at the 24 th week (1607.4±115.18 vs 1452.8±118.88 U/mg, P<0.01) and (103.63±6.44 vs 168.31±60.34 µmol/mg, P<0.01), respectively. Strong correlations were identified between body weight and bursal dimensions (r=0.603-0.864, P<0.01), while negative correlations existed between body weight and plicae dimensions (r=-0.844 to -0.903, P<0.01). Oxidative stress markers showed significant correlations with morphometric parameters: SOD correlated positively with body weight (r=0.958, P<0.01) and exhibited a negative correlation with LPO (r=-0.955, P<0.01). Chi-square analysis revealed highly significant associations between age and multiple parameters, including duck weight (χ 2 =12, P<0.01, OR=165), bursal dimensions, and oxidative markers. The study constitutes a comprehensive investigation of age-related histomorphological and ultrastructural alterations in Anas crecca , filling a knowledge gap of the relation between histomorphometric alterations and immuno-oxidative markers in that species. Also, it sets a new standard for aging research in avian species, providing a significant framework for future investigations in the immune system involution throughout the avian lifespan.