Pet Nutrition: Insect-based petfood
Whole larvae of the black-soldier fly (Hermetia illucens) and the yellow-mealworm beetle (Tenebrio molitor), or BSFL and YMW for short, have variable compositions. The crude protein and fat contents are 41 to 56 and 15 to 36 % in the dry matter (4-9). For puppies and kittens, the sum of methionine and cystine reflects the limiting amino acid in the two larvae species (6, 7). Lauric acid (C12:0) represents about 40% of total fatty acids in BSFL (5), but less than 0.2% in YMW (4).
Analysis of dried and partially defatted BSFL and YMW preparations used as petfood ingredients reveals around 60% crude protein, 15% crude fat and 10% crude fiber, but between-batch variation is considerable. Roughly half of the crude-fiber analyte could constitute chitin (5), but the N-acetylglucosamine polymer contributes little to the crude protein value.
In-vitro digestibility of protein in whole BSFL and YMW was 88.7 and 91.9% (6, 9), while the undigested residue appeared poorly fermentable by dog feces as microbiota source (9). Feces of dogs fed a BSFL-containing diet had increased chitin concentrations (10). For extruded foods with partially defatted BSFL or YMW, each accounting for about 30% of total dietary protein, apparent digestibilities of crude protein were 83.9 and 83.6% of intake in dogs and 79.8 and 80.4% in cats (11).
When dogs (12, 13) and cats (14) were switched to a formula with YMW as almost exclusive protein source, the owners did not note changes in feces consistency. For dogs fed commercial dry foods based on either lamb meal or BSFL, fecal scores differed statistically, but not meaningfully (10).
Free-ranging wolves (15) and feral cats (16) consume insects, the latter on average 1 weight% of their diet. Insects not only make up almost 1% of the animals brought home by British domestic cats (17), but are eaten also (18). Dogs seem to enjoy eating live BSFL (19) and dried mealworms (20) and were equally attracted towards olfactory cues from either commercial dry food, dried whole BSFL or YMW (21). In two-bowl preference tests, the intake ratio of dry foods with BSFL or YMW was about 60:40 in dogs and 40:60 in cats (11). Changing over dogs and cats to BSFL- or YMW-based, dry foods went smoothly (11, 12-14).
Forty six out of 50 pet owners gave positive feedback after learning they had been feeding an insect-based diet. Negative feelings, due to insect phobia and safety concerns, would be dropped for veterinary-prescribed diets with insects (22). Veterinarians seem interested in insect-based food as hypoallergenic alternative (23).
Insect-based, complete petfoods are on the market for up to three years. So far no health risks have been reported. YMW- and BSFL-containing diets did not negatively affect apparent pet health in studies lasting 28 (12-14) or 42 days (10), but clinical chemistry measurements were not done. An oral dose of 2.5 g cricket powder/kg bodyweight did not produce adverse effects in dogs (24). The impact of insect consumption on health in the long term is unknown. Insects might hold toxicants, either self-synthesized or derived from their feed substrates.
When at the farm gate, YMW (25) and BSFL (26) have emitted less greenhouse gas per kg live weight than chicken, pork or beef (27), but more than one kg of corn (28) or soybean (29). The ranking could persist after the processing toward isonitrogenous, dry protein concentrates for use as petfood ingredients. However, fair comparisons require calculations that allow not only for transportation and processing, but also for land use (change), energy efficiency, water pollution, co-products and their applications.
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