Apple pomace addition improves fermentation quality, nutritive value and bacterial community succession of alfalfa silage

Objective: Apple pomace is an abundant by-product rich in soluble carbohydrates, yet its potential to improve alfalfa silage fermentation remains underexplored.This study aimed to investigate the effects of apple pomace addition on the nutritional composition, fermentation quality, and bacterial community succession of alfalfa silage.Methods: Alfalfa (357 g/kg fresh weight (FW)) was harvested at the early flowering stage and ensiled with no apple pomace (CK), 5%FW apple pomace (AL), and 10%FW apple pomace (AH) for 60 days at room temperature (23±1℃).The nutritional composition, fermentation quality, and bacterial community were analyzed.Results: AH significantly improved silage quality compared with CK, evidenced by higher (P<0.05)lactic acid (28.41 vs. 15.24g/kg DM), acetic acid (6.8 vs. 2.3 g/kg DM), dry matter (498 vs. 358 g/kg FM), crude protein (193 vs. 154 g/kg DM), and water-soluble carbohydrates (57.7 vs. 45.1 g/kg DM), and lower (P<0.05)pH (3.75 vs. 4.81) and ammonia nitrogen (38.4 vs. 69.8g/kg TN).At the phylum level, Pseudomonadota (35.94%) and Bacillota (64.06%) dominated CK, whereas apple pomace supplementation increased Bacillota to 87.78% and decreased Pseudomonadota to 3.93%.At the genus level, apple pomace boosted Weissella, Lactiplantibacillus, and Bacillus.AL was dominated by Weissella (42.65%) and Bacillus (95.91%), while AH was predominantly colonized by Weissella (38.89%),Lactiplantibacillus (20.04%),Levilactobacillus (10.53%), and Lacticaseibacillus (8.79%), forming a more diverse lactic acid bacteria consortium.Spearman correlation analysis showed that Lactiplantibacillus and Weissella were positively correlated (P<0.05) with lactic acid and nutritional parameters, and negatively correlated (P<0.05) with pH.Functional profiling A c c e p t e d A r t i c l eindicated that apple pomace reshaped metabolic functions and upregulated enzymes related to carbohydrate degradation, energy metabolism, and substrate transport, promoting lactic acid accumulation.Conclusion: Apple pomace enhanced fermentation performance and nutrient retention in alfalfa silage, and a 10% inclusion rate is recommended for practical production.