Chlorella vulgaris and fat inclusion in diets for growing rabbits: effects on growth, diet digestibility, plasma metabolites, and caecal fermentations and microbiota
Microalgae, such as chlorella (Chlorella vulgaris), are protein rich sources (50-70% crude protein), providing essential nutrients such as omega-3 fatty acids, carotenoids, amino acids, and vitamin B 12 . This could result in an improved immune response, enhanced meat quality, and increased productivity in livestock species. The role of chlorella in rabbit nutrition remains underexplored, but existing research suggests positive effects on growth, reduced oxidative stress, and enhanced immune status with low chlorella inclusions (0.2% to 1%) in diets for growing rabbits. On the other hand, the impact of chlorella on diet digestibility, caecal activity, and targeted plasma metabolites remains unexplored. The present study evaluated growth performance, digestibility, plasma metabolites, caecal fermentations and microbiota composition in growing rabbits fed diets with different inclusion levels of chlorella (0% vs. 1% vs. 2%) and crude fat (3% vs. 5%). The inclusion of chlorella did not impact rabbit growth performance. However, diets with 5% crude fat compared to 3%, improved rabbit feed conversion ratio. Diets with 2% chlorella resulted in reduced digestibility of crude fat, while diets with 5% crude fat enhanced the digestibility of crude fat, hemicelluloses, and gross energy. Diets with 2% chlorella led to a decrease in plasma free NH 2 groups compared to diets with 1%, whereas diets with 5% crude fat reduced NEFA. Conversely, neither the inclusion of chlorella nor that of crude fat had an impact on other metabolites, such as glutamate, glutamine, D-lactate, creatinine, glucose, urea, inorganic P, and calcium. The characteristics of digestive organs, caecal fermentations, and microbiota were unaffected by the inclusion of chlorella or crude fat.  In conclusion, the inclusion of chlorella up to 2% in diets for growing rabbits did not affect diet nutritional value or rabbit performance and caecal activity. On the other hand, the inclusion of crude fat at 5% could improve the overall farm efficiency.