Vegetable Harvest Residues as Alternative Forages: Feed Value, in Vitro Fermentation, Methane Production, and Digestibility of Fresh, Ensiled, and Pelleted Tomato Plant Residue

Abstract

Vegetable harvest residues are increasingly evaluated as alternative forage resources for ruminants, but their nutritive value depends strongly on crop species, preservation method, and processing form. This study evaluated the post-harvest green aerial vegetative parts (stems and leaves) of greenhouse-grown tomato plant residues (Solanum lycopersicum L., cv. Vermilenza F1) processed into three forms: fresh residue (TR-F), residue ensiled in laboratory-scale silos without additives for 60 days (TR-S), and residue dried and pelleted into 6-mm cylindrical pellets (TR-P). Chemical composition, cell wall fiber fractions, relative forage quality indices, in vitro gas production kinetics, methane production, and in vitro true digestibility (IVTD) were determined. Processing significantly affected the nutritive value and fermentation parameters (P < 0.05). The pelleted form (TR-P) exhibited the highest relative feed value (RFV) alongside lower crude fiber (CF), neutral detergent fiber (NDF), acid detergent fiber (ADF), and cellulose contents compared with the fresh form (TR-F). However, TR-P exhibited the highest acid detergent insoluble protein (ADIP) content, indicating heat- or pressure-induced protein binding and reduced protein availability. Ensiling (TR-S) resulted in the highest relative forage quality (RFQ) and the lowest methane production (5.79 mL/200 mg DM), but reduced total gas production, energy values, short-chain fatty acid (SCFA) production, microbial protein synthesis (MPS), and organic matter digestibility (OMD) compared with the fresh form (TR-F). The fresh form displayed the highest fermentation activity and energy potential, showing the greatest total gas production (79.85 mL/200 mg DM), 24-h gas production (47.43 mL/200 mg DM), metabolizable energy (ME; 8.49 MJ/kg DM), net energy for lactation (NEL; 5.53 MJ/kg DM), SCFA (1.04 mmol/L), MPS (2.49 mg/mL), and OMD (77.79%). In vitro true digestibility was slightly lower in TR-P (64.39%) than in TR-F (66.74%) and TR-S (66.21%). Tomato plant residue showed promising potential as an alternative source of roughage for ruminants. Although fresh tomato residue retained the highest biological energy and fermentability, ensiling with or without additives is recommended as the most effective preservation strategy to ensure aerobic stability and mitigate enteric methane emissions. Pelleting serves as an efficient densification and handling alternative, provided processing temperatures are controlled to minimize heat-induced protein binding to fiber fractions. Further in vivo studies are needed to evaluate intake, digestibility, and animal performance.