Effects of Dietary Inclusion of β-Hydroxy-β-Methylbutyrate on Growth Performance, Fat Deposition, Bile Acid Metabolism, and Gut Microbiota Function in High-Fat and High-Cholesterol Diet-Challenged Layer Chickens

Excessive lipid deposition in layer chickens due to inappropriate feeding adversely affects egg production; however, nutritional manipulation methods to deal with this issue are still limited. β-hydroxy-β-methylbutyrate (HMB), a metabolite of L-leucine, was recently reported as a lipid-lowering nutrient in mice and pigs, although its role in layers had not been investigated. Here, we employed high-fat and high-cholesterol diet (HFHCD)-challenged growing layers as an obese model to explore HMB function in the regulation of lipid metabolism and the potential mechanisms involved. We found that dietary supplementation with (0.05% or 0.10%) HMB significantly reduced HFHCD-induced bodyweight growth in layers, mainly due to reduction in abdominal fat deposition. Mechanistically, HMB supplementation enhanced hepatic bile acid synthesis from cholesterol through elevating expression of Cyp7a1, a gene coding a key enzyme in bile acid synthesis. Furthermore, 16S rRNA gene sequencing revealed that HMB supplementation remodeled the diversity and composition of the layers' cecal microbiota, and the abundance of Bacteroidetes at the phylum level were especially affected. Correlation analysis further indicated a strong negative association between Bacteroidetes abundance and lipid metabolism-related parameters. Taken together, these data suggest that dietary HMB supplementation could improve abdominal fat deposition in layers, probably through modulating hepatic bile acid synthesis and gut microbiota function.