Fermentation characteristics, chemical composition, microbial quality and in vitro ruminal fermentation of almond hulls silages treated with different additives

Almond hulls (AH) are the main by-product of almond production and are currently used as ruminant feed after field drying. This study evaluated the feasibility of ensiling AH as an alternative preservation method and assessed the effects of different silage additives on fermentation characteristics, chemical composition, microbiological quality and in vitro ruminal fermentation of AH silages. Four silage treatments were studied: control (CON; without any additive), formic acid (FA; 4 mL/kg AH), a mixture of acetic and lactic acids (ALA; 2 mL of each acid/kg AH), and Lentilactobacillus buchneri (LB; 5 × 10⁹ colony forming units/kg AH). Almond hulls were ensiled in vacuum-bags at 530-550 g dry matter/kg and stored for 90 d at room temperature. Compared with CON, all additives reduced ( P < 0.05) silage pH to reach below 4.60. Both FA and ALA silages showed the lowest ( P < 0.05) dry matter losses (< 25 g/kg AH), whereas LB treatment promoted stronger heterofermentative activity and resulted in the greatest ( P < 0.05) concentrations of lactic and acetic acids. No pathogenic bacteria ( Escherichia coli , Salmonella spp., Listeria spp., Clostridium perfringens and Staphylococcus coagulase +) were detected in any silage, and all additives decreased ( P < 0.05) the growth of yeast and molds compared to CON silages. In vitro 24-h incubations with sheep ruminal fluid showed that LB silages had faster ( P < 0.05) fermentation rates and lower ( P < 0.05) acetic to propionic ratios than CON silages, but FA treatment decreased ( P < 0.05) the production of volatile fatty acids indicating reduced fermentation. A secondary objective of this study was to assess the changes in fermentation characteristics and chemical composition of AH silages over the storage period, and therefore additional silage bags were opened at 0, 4 and 21 d. Compared with CON silage, all additives produced a faster and greater pH decline and resulted in lower concentrations of NH 3 -N at both 4 and 21 days of storage. Except for FA silages, concentrations of lactic acid increased gradually with storage time for all other treatments. Propionic acid was not detected in any silage at any time and acetic concentrations increased with storage time in all silages except FA silage. Concentrations of butyric acid were lower than 0.30 g/kg DM in all silages at all sampling times except for LB silages at 90 d (2.22 g/kg DM). The most marked change in chemical composition over storage was the reduction in the concentration of water-soluble carbohydrates, being the reduction more pronounced for ALA and LB treatments (32.5 and 53.9%, respectively) than for CON and FA (10.2 and 8.0%) silages. The results indicate that ensiling could be a feasible alternative for preserving almond hulls in areas where weather conditions compromise their optimal drying. • Almond hulls (AH) were ensiled with different additives • Ensiling AH at 540 g dry matter/kg without additives resulted in good preservation • Formic acid reduced ruminal fermentation of AH silages • Both acetic-lactic acids and L. buchneri lowered pH and improved silage quality • Ensiling offers a viable alternative to field drying for AH conservation