Agro-Industrial Residues as Additives in Tropical Grass Silage: An Integrative Review

Agro-industrial residues can improve the fermentation quality of tropical forage grass silages when used as additives, but a systematic synthesis of their effectiveness is limited. This integrative review aimed to identify the main residues used as additives in silages and assess their effects on the fermentation process. Following the PVO (population, variable of interest, and outcome) protocol, searches were conducted in the Wiley Online Library, Web of Science, and SCOPUS databases, with no restrictions on language, time, or region. The guiding question was: “What are the main agro-industrial residues used as additives in the ensiling of tropical forage grasses?” Of the 1414 documents initially retrieved, 138 were selected after screening titles, abstracts, and keywords. After removing duplicates and full-text evaluation, 58 studies met the inclusion criteria. Brazil led in the number of studies (89.66%). Elephant grass (Pennisetum purpureum Schum.) was the most studied forage (34.21%). Citrus pulp (13.79%) and coffee husk (12.07%) were the most evaluated residues. The addition of residues promoted a reduction in pH (66.07%), ammonia nitrogen (71.74%), buffer capacity (57.14%), and the concentrations of acetic (52.17%), propionic (52.63%), and butyric (55.00%) acids. Lactic acid content increased in 32.76% of studies; gas and effluent losses decreased in 69.57% and 86.36% of cases, respectively. Citrus pulp and coffee husk are the most used residues, enhancing fermentation quality. It is concluded that the use of agro-industrial residues in the ensiling of tropical forage grasses has the potential to improve fermentation quality.