Dietary crude glycerol as an energy source in broiler chickens: a meta-analysis

Objective: This meta-analysis evaluated the effects of dietary crude glycerol (CG) supplementation on growth performance, carcass traits, meat quality, and blood biochemical parameters in broiler chickens. Methods: A systematic search of peer-reviewed studies in Scopus, ScienceDirect, and Google Scholar was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses protocol. Twenty-five eligible studies were included. Effect sizes were calculated as standardized mean differences using a random-effects model in Open-MEE software. Subgroup analyses were performed according to strain, sex, rearing phase, and inclusion level. Results: CG supplementation increased body weight gain (p<0.05) and improved feed conversion ratio (p<0.05), while feed intake was unaffected. Among carcass traits, breast yield increased (p<0.05), whereas carcass yield and thigh yield were not affected. CG inclusion also reduced meat ash content and ultimate pH, while drip loss increased, indicating potential negative effects on water-holding capacity. Blood biochemical indices, including reduced alanine aminotransferase and elevated alkaline phosphatase, indicated adaptive physiological responses without evidence of toxicity. Subgroup analyses revealed that strain, sex, and inclusion level moderated growth outcomes (p<0.05). Conclusion: CG can be incorporated into broiler diets as an alternative energy source to enhance growth performance without compromising carcass yield. However, its influence on meat quality highlights the need to optimize inclusion levels and consider variability among glycerol by-products before large-scale application.