Cutting-edge exploration of insect utilization in ruminant nutrition—feature and future: a systematic review and meta-analysis

There has been a growing interest in using insects as sustainable protein sources for ruminant feed, such as the adults of the two-spotted cricket (Gryllus bimaculatus), larvae of the mealworm beetle (Tenebrio molitor), black soldier fly (Hermetia illucens), and pupae of the silkworm (Bombyx mori). The advantages of these insects over other plant materials lie in their elevated levels of crude protein and fat. However, this interest lacks a comprehensive understanding of the impact of insects on the ruminal fermentation processes, including digestibility and gas production, as well as the impact on animal performance and related health aspects. This review offers a comprehensive analysis of ruminal fermentation indices across diverse insect species. Employing descriptive and meta-analysis methodologies, we examined the impact of incorporating insect-derived meals in ruminants’ diets. Moreover, we evaluated the growth performance and biochemical parameters of blood in ruminants when species such as Tenebrio molitor, Hermetia illucens, Oriental Hornet (Vespa Orientalis), and Bombyx mori were incorporated into ruminants’ diets. The meta-analysis was performed on a limited dataset of 14 in vitro and eight in vivo trials, investigating insect meal as a potential feed source. A comparison is drawn between these insect-based feeds and conventional dietary sources such as soybean meal, alfalfa hay, and commercial concentrate diets. Our meta-analysis revealed that incorporating Gryllus bimaculatus and Hermetia illucens to partially replace protein sources in ruminants’ diet did not adversely affect digestibility, ruminal fermentation, and ruminant production, supporting the feasibility as a feed ingredient for ruminant animals. In addition, the oriental hornet showed an overall higher outcome on the final BW, ADG, digestibility, and volatile fatty acid (VFA) production, suggesting the promising effect of this insect for future use in ruminants. The data also indicates that dietary insect inclusion levels should not exceed 30% (DM basis) to achieve an optimal ruminal fermentation profile. Furthermore, it offers comparative insights into the nutritional value of these insects, which warrant further investigation at the in vivo level. Ultimately, the existing understanding of the nutritional utilization potential of these insects by ruminants, particularly concerning macro- and micronutrients, is evaluated and revealed to be significantly constrained.