The effect of capsaicin based natural and processed feed additives on fattening performance and welfare level of Japanese quail (Coturnix japonica) statistical modeling

This study consists of two phases investigating the performance and welfare of Japanese quails (Coturnix japonica). The first phase examines the effects of diets containing different levels of Urfa pepper waste (Capsicum annuum L.) and a capsaicin-based commercial feed additive (ID Phyt Capcin) on quail performance, carcass traits, blood parameters, and egg production. The second phase evaluates the impact of welfare on growth, physical activity, biological and physiological stress, and the immune system. The performance phase lasted a total of nine weeks and included seven experimental groups. Urfa pepper waste and ID Phyt Capcin were incorporated into diets at 2.5%, 5%, and 7.5% levels. Results indicated that the 7.5% Urfa pepper waste group achieved the highest body weight at the end of the first three weeks (p<0.05), whereas no significant difference was observed among groups at six weeks (p>0.05). Feed intake was highest in the 5% and 7.5% Urfa pepper waste groups during the 0–3 week period (p<0.05), with no significant differences detected among groups in the 4–6 week period (p>0.05). Feed conversion ratiowas lowest in the 5% ID group and highest in the 7.5% Urfa pepper waste group (p<0.05). Carcass analysis revealed an increase in gizzard weight in the Urfa pepper waste group (p<0.05), while heart and spleen weights significantly decreased (p<0.05). Triglyceride levels were lower in the Urfa pepper waste groups but higher in the ID groups (p<0.05). Egg production was highest in the 7.5% ID group (p<0.05), whereas egg yolk color was significantly darker in the Urfa pepper waste groups (p<0.05). These findings highlight that the type and dosage of feed additives exert varying effects on performance parameters. The welfare phase assessed quail welfare levels using partial least squares structural equation modeling (PLS-SEM). A hierarchical component model (HCM) was employed, where welfare was designated as a higher-order component (HOC) and physiological variables as lower-order components (LOCs). The results demonstrated that welfare significantly influenced physical activity (0.791), immune system function (0.567), and growth (0.903). Welfare explained 62.6% of the variance in physical activity, 32.1% in immune system function, and 81.6% in growth. These findings underscore the critical role of welfare in shaping key biological processes in quails and provide a robust methodological framework for welfare assessment.