Are insects a solution for feeding ruminants? Legislation, scientific evidence, and future challenges

The growing interest of the scientific community on the inclusion of insect-derived products in ruminant diets is leading to a boost of research papers on this topic. Even though in absolute terms the increase in the number of published papers is limited—because limited is also the literature on this topic—the scientific production in 2022 equals the scientific production of the former 19 years (about 10 papers published in each above-mentioned time-period). The reason is that insect-derived products are considered not only promising but also sustainable feed ingredients, thanks to the ability of insects to successfully convert relatively low-value agri-food waste into high-quality proteins and fats. The insect crude protein content varies, according to insect stage and processing technology, from 7.5% to 91% (dry matter—DM—basis), while the crude fat values range between 46% and 64% (DM basis) (Finke and Oonincx, 2023). Moreover, their production is characterized by limited environmental footprint. A generalization of their use in ruminant farming could contribute to limit its impact and to move towards a Circular Economy model (Gasco et al., 2020). However, this requires that reality meets expectations. On this basis, in this review we provide information about the state-of-the-art on the use of insects in the nutrition of domestic ruminants, including an overview of the current legislation worldwide and the hitherto known effects of insect-derived products on nutrient digestibility, animal performance, and ruminal biohydrogenation (BH). Following the identified differences in legislative frameworks and the potential application of insect products, information will be provided by dividing them into protein-rich feedstuffs, lipid-rich products (differentiating full-fat meals and free oils), and other insect-derived ingredients for ruminant diets.