Chlorella vulgaris supplementation in broiler feed: relation between dosage and effect on intestinal health under an Eimeria vaccine challenge

The broiler industry is facing increasing challenges due to the intensification of production and the associated rise in intestinal health issues. Chlorella vulgaris , a nutrient-rich microalga, may offer a sustainable antibiotic alternative to support gut health through its bioactive compounds. In this study, a dose-response trial was conducted to evaluate the health-promoting potential of microdoses (0-2%) of autotrophically grown C. vulgaris in broiler diets. Broilers were subjected to a mild Eimeria challenge to mimic industrial conditions and to induce stress in the intestinal tract. No significant linear relations were found between C. vulgaris inclusion level and intestinal histomorphology parameters. However, antioxidant capacity showed a trend toward linear increases with increasing algae inclusion. Feed viscosity increased significantly with C. vulgaris inclusion in the starter phase and fecal viscosity on day 23 showed a positive linear relation. A linear increase in breast meat redness (a*) and yellowness (b*) was observed on days 16 and 23. Body weight development and organ growth (bursa and spleen) were not significantly affected. In conclusion, while inclusion of C. vulgaris at microdose levels did not significantly alter intestinal morphology or growth performance, trends in antioxidant capacity, meat color, and spleen growth suggest potential health-promoting effects.