Background: Insects have gained global recognition as a sustainable alternative to conventional protein sources, with the potential to address global food and nutrition insecurity as well as reduce the ecological footprint of animal production. While insects are part of traditional diets in many regions, the Western world is still unwilling to consume insects in their diets, mainly due to acquired distaste and a lack of information on their nutritional benefits. Studies demonstrating similar or higher digestibility and protein quality of insects compared with conventional proteins can aid their acceptance as viable food sources.

Additionally, a great deal of interest has been placed on the biofunctional properties of insects owing to their ability to improve gut health, leading to good growth performance without any negative impact on animal health. These functional properties of insects can be valuable in animal production, particularly for overcoming the challenges associated with weaned piglets. Therefore, the overall aim of this thesis is to provide scientific evidence and add to the current knowledge on the suitability of insects as food and feed.

Methods: This thesis is based on two experimental studies and a review. Paper I reports the protein quality of five insect species (LMW, lesser mealworm; YMW, yellow mealworm; HC, house crickets; BC, banded crickets; and BSF, black soldier fly) based on the digestible indispensable amino acid score (DIAAS) recommended by the Food and Agriculture Organisation (FAO). A 6×6 Latin square design

was used in this study. During the experiment, all six cannulated pigs were fed one of the six different diets (one nitrogen -free and five insect-based diets) every experimental week for six weeks so that all pigs received all diets by the end of the experiment; hence, each diet was assessed in six replicate pigs.

An indigestible marker was used to assess digestibility. Individual insect, diet, and ileal digesta samples were collected to assess their chemical composition. Paper II aimed to evaluate the effects of three insect (LMW, YMW, and BSF) based diets (partially replaced with soybean protein concentrate) on growth performance, gut health, and immune response in weaned piglets compared with soybean protein

(control). A total of 96 piglets were randomly assigned to one of the four diets (24 piglets per diet) for 14 days. All the animals were euthanised at the end of the experiment. All insect species and diet samples were collected to assess their chemical composition, blood for diamine oxidase and D-lactate

concentration, stomach digesta for pH, small intestine and colon digesta for pH, microbial and volatile fatty acid analysis, and mucosal scraping of the small intestine for secretory IgA concentration. Paper III reviewed suitable methods for evaluating digestibility and protein quality, focusing on methods that have reported on the protein quality of insects. Additionally, the literature reviewed was based on the protein and AA digestibility of insects used in livestock feed (especially poultry and pigs) and their effect on growth performance.

Results: In Paper I, sulphur AAs (methionine + cysteine) were the limiting AAs in mealworm and

cricket species for the age groups above six months old. For young children and those older than three years, the DIAAS of both cricket species was higher than 75. Only one species of mealworm, LMW, had a DIAAS > 75 for individuals older than three years. The study in Paper II found that insect-based diets fed to weaned piglets did not affect growth performance significantly (P ˃ 0.05), but were comparable to soybean-based diets. There was no significant difference (P ˃ 0.05) in gut health and immune parameters between the diets. Only piglets fed the LMW and YMW diets had significantly (P < 0.05) lower diamine oxidase (DAO) concentrations (321 and 309 ng/ml, respectively) than those fed the control diet (382 ng/ml).

Conclusion: Crickets and mealworm species are good protein sources for older children, adolescents, and adults, with the cricket species having slightly better DIAAS than mealworms. While assessing the protein quality of insects using DIAAS, the standard nitrogen-to-protein conversion of 6.25 needs reconsideration as this conversion does not account for non-protein-nitrogen present in insects, thereby underestimating the DIAAS of insects. Additionally, the non-protein-nitrogen content of insects has challenged the direct comparison of insect protein quality with studies of other food sources. Sulphur AA was the first limiting amino acid in all four species of crickets and mealworms.

The inclusion of mealworms or BSF supported the growth and overall health of weaned piglets. The piglets fed insect-based diets and soybean-based diets performed equally in terms of growth performance and all related gut health parameters. Reduced plasma DAO concentrations in piglets fed with mealworms indicated protection of the intestinal mucosal barrier function.

Overall, these studies confirmed that insects are promising alternative protein sources for human food and animal feed, although further research is required to document and understand the properties and qualities of each of the relevant insect species. Their protein quality, comparable growth performance to that of conventional feed, and positive impact on gut health parameters highlight their suitability as viable alternatives. Additionally, mealworm-based diets contribute to improved gut health by protecting the intestinal mucosal barrier in weaned piglets. These findings expand our knowledge and pave the way for a more sustainable and innovative approach to food and feed production. A more comprehensive

understanding of the potential use of insects for food and feed requires further research, with careful consideration of the methods applied.