From waste to feed: In vitro assessment of spent silkworm by-products and manure-raised housefly as soybean meal substitutes in ruminant feed.

The study aimed to evaluate the efficiency of utilizing insects-spent silkworm pupae, either fed naturally on mulberry leaves (SW-N) or on an artificial diet (SW-A), as well as housefly larvae (HF-L) and pupae (HF-P) reared on swine manure-as alternative feeds to replace soybean meal in ruminant diet (60% grass: 40% soybean meal) at inclusion levels of 5%, 10%, 20%, and 40%. This study assessed their nutritional value and investigated their effects on nutrient digestibility, rumen fermentation profile, and methane (CH(4)) production using an in vitro batch culture technique. The results showed that the tested insects had higher protein and fat contents than soybean meal. Fatty acid analysis revealed that SW-N and SW-A were rich in unsaturated fatty acids (70.9% and 60.6%, respectively), whereas HF-L and HF-P contained 52.4% and 51.4%, respectively. The inclusion of SW-N and SW-A at levels up to 40% in the diet had no negative effects on volatile fatty acids (VFA) production, increased ammonia-nitrogen concentration and nutrient digestibility, and decreased CH(4) production by 20%. Although HF-L and HF-P supplementation reduced CH(4) production by up to 25%, their inclusion at levels exceeding 10% inhibited rumen fermentation. In conclusion, SW-N and SW-A can effectively replace soybean meal in ruminant diets; while the inclusion of HF-L or HF-P at levels exceeding 10% is not recommended. These insects represent a promising strategy for sustainable feed development with CH(4)-reduction potential.