Are Insects a Feasible Option or Just a Hyped Promise in Ruminant Nutrition? A Systematic Review of What Has Been...

Insects have emerged as a promising sustainable feed alternative for ruminants, offering high nutrient density and potential environmental benefits in the context of growing pressures on conventional protein sources. This systematic review critically evaluates the state-of-the-art literature written in English and published in peer-reviewed journals from 2015 to 2025 on the use of insect-based feeds in ruminant nutrition, synthesising evidence from in vitro and in vivo studies, discussing their outcomes and elucidating underlying mechanisms to guide future research. Most insect species studied include black soldier fly (Hermetia illucens) larvae, housefly (Musca domestica) larvae, adult crickets (Gryllus bimaculatus), silkworm (Bombyx mori) pupae, and mealworm (Tenebrio molitor) larvae, with studies highlighting their favourable chemical composition, particularly high protein content and rich fatty acid profiles. In vitro and in vivo research, though occasionally inconsistent, shows promising effects on rumen fermentation, methane production, growth performance, product quality, and animal health. Nevertheless, inconsistent results, driven by variations in insect species, processing methods, and inclusion levels, highlight significant knowledge gaps. Challenges include non-standardised nutrient profiling, limited long-term health and performance studies, regulatory disparities, high production costs, scalability constraints, and underexplored consumer acceptance of sensory and market aspects. While insects offer opportunities for waste bioconversion and reduced ecological footprints, their integration requires targeted research into optimised feed formulations, longitudinal health studies, and robust regulatory frameworks. This review emphasises the necessity of multidisciplinary research to clarify the nutritional, environmental, and economic viability of insect-based feeds, paving the way for sustainable ruminant production systems.