Edible Insects in Pet Food: Does the Rearing and Processing Alter the Nutritional Value?

Despite the legal approval, the use of edible insects in food for dogs and cats is still limited and there are still some fundamental questions before the widespread application will kick off. This research focused on the nutritional value of yellow mealworms (YMW) and black soldier fly larvae (BSFL) reared, harvested, and dried in different ways. For YMW, standard rearing crates were harvested over different sieve meshes, dividing them according to width. For BSFL, differences were created by different rearing densities (10,000, 20,000, 30,000 and 40,000 per crate of 60 by 40 cm). Concerning the effect of drying methods on nutritional quality, 3 different techniques— hot air at different temperatures (60°C, 90°C and 120°C), freeze-drying, and microwave drying — were evaluated using proximate analyses and in vitro digestibility trials. For YMW, larvae smaller than 2.5 mm had a higher protein content than the larger larvae (p = 0.002); however, this was compensated by a lower dry matter (DM) digestibility (p < 0.001) due to a higher crude fibre content (p < 0.001). Nitrogen digestibility was very high regardless of size (97%–98%). For BSFL, the only significant differences were in higher DM (p < 0.001) of the biggest larvae (10,000 per crate). In contrast to YMW, the biggest BSFL had the lowest in vitro digestibility (only 48% for DM and 83% for nitrogen compared to 60% for DM and 86% for nitrogen for the smaller sizes (p < 0.001)). The drying methods had no big impact on YMW on DM (85%–88%) and nitrogen (96%–98%) digestibility values. For BSFL, digestibility of DM and nitrogen were 57%–66% and 93%–97%, respectively, with the lowest values for drying at 120°C.