Journal of Animal Research and Nutrition

The present study aimed to evaluate the potential of yellow mealworms (Tenebrio molitor) reared using local agricultural byproducts as an alternative feed for monogastric and ruminant animals. The mealworms were raised on oat-based (OB) and wheat-based (WB) by-products, and their nutritional properties and in vitro digestibility were evaluated, simulating the digestive system of both monogastric and ruminant animals.

Furthermore, the gut microbiome of mealworm larvae was studied. Crude fat and most minerals were higher in larvae fed WB than those fed OB (P<0.05), reflecting the nutritional profiles of the substrates. Larvae and pupae generally shared a common nutritional profile: Lower contents of crude fiber, crude protein, and total amino acids, and higher crude fat, total fatty acids, and gross energy levels compared to adults. Total essential and non-essential amino acid contents in larvae and pupae were similar to those of a commercial soybean meal (SBM). The in vitro dry matter and protein digestibility of larvae and pupae were similar to SBM and significantly higher (30%) than the values for adults for both monogastrics and ruminants. Firmicutes and Proteobacteria were the most abundant gut microbial phyla in larvae, and the gut microbiome revealed remarkable plasticity in response to altered nutritional status, such as starvation. A new insight into the nutrition of mealworm's metamorphic stages fed on agricultural by-products and how feeding modulates the larval gut microbiome provides an innovative approach to exploit mealworms as a sustainable and alternative animal feed source in the future.

Livestock Sector

The world's human population is growing rapidly, and ensuring food security is a global concern. The livestock sector plays a vital role in agricultural food production, contributing 15% of total food energy and 31% of dietary protein globally. Due to increased calorie intake and the nutritional shift toward animal-based products worldwide, it is anticipated that future demands for livestock-based products will increase even further, particularly in low- and middle-income countries. Such increased demands for livestock products can be fulfilled through the identification and utilization of alternative animal feeding resources, as they play a crucial role in establishing a sustainable livestock sector in the future. In recent years, different insect species have been identified as promising alternative and more sustainable feed ingredients for livestock due to their capability to convert waste or by-products into biomass rich in protein and other valuable nutrients.

Among insects, the yellow mealworm (Tenebrio molitor) has been identified as one of the few candidate species with the potential for large-scale commercial production. Mealworms can potentially be grown under a variety of agricultural and other low-quality organic substrates and can be utilized as alternative nutrient sources for livestock, mainly monogastric animals. In Nordic countries, self-sufficiency for domestic animal feed resources is relatively low. Thus, the local production and utilization of new feed ingredients, such as mealworms, would contribute to an increased domestic supply of raw ingredients for feed industries in the region. This requires knowledge of whether locally available bioresources, such as agricultural byproducts from the Nordics, can be efficiently utilized to produce mealworm biomass of high nutritional quality for production animals.

The ability of mealworm larvae to use various substrates may depend upon the interaction between the larvae and their gut micro biome. For example, specific gut bacterial strains of the genera Klebsiella, Pseudomonas, and Serratia found in mealworm larvae were linked to bio plastic biodegradation. Furthermore, a substantial change in the larval intestinal microbial community of mealworms was observed s with dietary modification, i.e., Lactobacillus and Mucispirillum were associated with a plastic-enriched bran diet. However, changes in the gut microbial communities of mealworm larvae in response to an altered short-term nutritional status are largely unknown. This study investigates the potential changes in the gut microbial population of mealworm larvae exposed to nutritional challenges. Such data would be important in determining whether the gut microbiome could be used to improve the feed efficiency of mealworm larvae in commercial mealworm farming.

The mealworm is a holometabolous species, and its life cycle consists of four distinct metamorphic stages: Egg, larva, pupa, and adult. Previously, the biomass of mealworm larvae has been investigated in terms of their potential nutritional value as feed for animals. For example, including mealworm larvae in the diets of pigs and poultry improved their nutrient digestibility and growth performance. It is noteworthy that mealworms, at their different metamorphic stages, can have unique chemical compositions; for example, the level of chitin can affect the potential of utilizing them as animal feed ingredients. However, the impacts of such metamorphic stages on the nutritional profile and their utilization as animal feed ingredients have often been overlooked. This study aims to characterize the metamorphic-stage-specific nutritional compositions and in vitro digestibility (for both monogastric and ruminant animals) of mealworms.

The objectives of this study were to test the hypotheses that a) high nutritional quality of mealworms is achieved by using agricultural by-products that are locally available in the Nordic region, b) nutritional value and digestibility of mealworms are dependent on their metamorphic stages, and c) short-term nutritional challenges modulates the gut microbiome of mealworm larvae.