Sustainable production of housefly (Musca domestica) larvae as a protein-rich feed ingredient by utilizing cattle manure

Abstract

The common housefly, Musca domestica, is a considerable component of nutrient recycling in the environment. Use of housefly larvae to biodegrade manure presents an opportunity to reduce waste disposal while the rapidly assimilated insect biomass can also be used as a protein rich animal feed. In this study, we examine the biodegradation of dairy cattle manure using housefly larvae, and the nutritional value of the resulting larva meal as a feed ingredient. Our results demonstrated that dairy cattle manure presents a balanced substrate for larval growth, and the spent manure showed reductions in concentration of total nitrogen (24.9%) and phosphorus (6.2%) with an overall reduction in mass. Larva yield at an optimum density was approximately 2% of manure weight. Nutritional analysis of M. domestica larva meal showed values comparable to most high protein feed ingredients. Larva meal was 60% protein with a well-balanced amino acid profile, and 20% fat with 57% monounsaturated fatty acids, and 39% saturated fatty acids. Larva meal lacked any significant amount of omega-3 fatty acids. Evaluation of micronutrients in larva meal suggested that it is a good source of calcium and phosphorus (0.5% and 1.1% respectively). The nutritional value of larva meal closely matches that of fishmeal, making it a potentially attractive alternative for use as a protein-rich feed ingredient for livestock and aquaculture operations.

Fig 1. Effects of intensive rearing on housefly larvae growth and development.

Twenty-five gram manure samples were incorporated with 1, 2, 4, 8 or 16, housefly eggs/gram manure (n = 7). Eggs were allowed to hatch and larvae were harvested after 5 days of growth. For the different larvae densities: (A) Harvest weight was determined by weighing all harvested larvae at the end of the experiment; (B) Individual larva weight was calculated by dividing the total harvest weight by the number of harvested larvae’ (C) Larva survival rate was calculated by dividing the number of harvested larvae and/or pupae by to the number of eggs incorporated; (D). Pupation rate was calculated by dividing the number of harvested larvae and/or pupae by the number of eggs incorporated. Values represent means ± SEM. Groups not connected by same letter are significantly different (P < 0.05).

Fig 2. Relationship between density and migratory behavior of housefly larvae in dairy cattle manure.

(A) Larva migration was observed over the 7 days of growth. Migration depth was calculated as the distance within manure (cm) that larvae were able to reach during the experiment. Data are represented as medians, 25^th to 75^th percentile as hinges, and range as whiskers. (B) Larvae outmigration rate was calculated as the percentage of larvae exiting or ultimately trapped in the manure environment at days 5, 6 and 7 of growth. This rate was compared across different densities of incorporation (1, 3, 5 and 7 larvae/g of fresh manure; n = 4/group).

Fig 3. Dairy cattle manure degradation resulting from housefly larvae growth.

(A) Housefly eggs incorporated in 25 g of fresh dairy cattle manure at different densities (0, 1, 2, 4, 8 or 16 eggs/g) were allowed to hatch and grow (n = 7/group). Decrease in manure weight after growth for 5 days was measured after harvesting larvae for the different groups. (B) Manure degradation rate was calculated as the percentage change in manure weight for each egg density group relative to the change in the control group after 5 days of larvae growth. Values represent mean ± SEM. Groups not connected by same letter are significantly different (P < 0.05).