Frass from black soldier fly larvae as a sustainable by-product feed: in vitro evaluation and nutritional clustering for environmentally-friendly ruminant diets.

Abstract

This study aimed to assess the chemical composition, in vitro gas production, dry matter (DM) and crude protein (CP) degradability, and multivariate classification (hierarchical cluster and principal component analysis, PCA) of frass, barley, corn, soybean meal, and alfalfa hay. Chemical analysis indicated that frass had the lowest DM content, while its CP concentration was higher than that of barley, corn, and alfalfa hay but lower than that of soybean meal. The ether extract content of frass was comparable to barley but lower than corn and soybean meal. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) levels in frass were intermediate relative to other feeds. Gas production analysis showed that the asymptotic gas production (B) of frass was comparable to that of corn, whereas fractional rate constant of gas production (c) was the lowest, differing significantly only from barley. Energy-related parameters, including metabolizable energy (ME), organic matter digestibility (OMD), and short-chain fatty acids (SCFA), were highest in corn, with frass exhibiting higher values than alfalfa hay. DM degradability analysis revealed that frass had the highest soluble and very rapidly degradable fraction (a) and a lower insoluble but potentially fermentable fraction (b) compared to other feeds. CP degradability exhibited a similar pattern. Cluster analysis classified frass as an independent group, while PCA (explaining 67.9% of the variability) positioned it closer to alfalfa hay, primarily due to similarities in fiber and mineral composition. These findings suggest that frass, produced from BSFL reared on a Gainesville diet, represents a promising alternative feedstuff for ruminants. However, further in vitro and in vivo studies are required to evaluate its nutritional potential under varying dietary conditions and its impact on ruminant performance.