Due to the increase of consumption of food products by the population, especially of animal origin, the need of the livestock industry including sheep breeding for high-quality feed from an ecological point of view also increases. Recently, insects have received a lot of attention as a source of feed protein in the diet of farm animals. This is evidenced by numerous studies on the nutritional value and use of larvae of Black soldier fly (Hermetia illucens), Green-bottle fly (Lucilia Caesar), House fly (Musca domestica), meal worm (Tenebrio molitor), silkworms (Bombyx mori), and crickets (Gryllusbi maculatus) as food for farm animals. It is well known from foreign literature sources about the use of additive from silkworm pupae in the ration of sheep, as well as meal from crickets as the source of protein in the diet of lambs. The silkworm is a monophage eats in only at the caterpillar stage absorbing and accumulating the necessary nutrients and water from the mulberry leaves. The analysis of the works of foreign authors shows that the protein content in the silkworm caterpillars depending on the breed ranges from 63,02 to 67,99 %. However, the analysis of the content of the main nutrients in the section of silkworm breeds as well as the age of the caterpillars was not carried out in the works of domestic scientists. This research presents data on the nutrient content and metabolic energy in silkworm caterpillars by age depending on the breed for further development of the feed additive from silkworm biomass and its use in sheep breeding. In the course of the conducted research, the following results have been obtained. So, at the end of the 4th age on average the caterpillars have a body length of 4,5–5,0 cm, the weight of one caterpillar is 0,6–0,7 g. The largest size and weight are the caterpillars on 10 days of the 5th age; their body length on average for the studied breeds was 8,0–8,5 cm, the weight of one caterpillar was 4,5–5,5 g. The optimal stage of development of silkworm caterpillars for the production of feed additive is 10 days in the 5th age. During this period the caterpillars of the studied breeds Kavkaz-1, Kavkaz-2, Belokokonnaya-1, Belokokonnaya-2 contain protein from 62,71 to 66,55 %, fat from 14,81 to 16,95 %, fi ber from 2,36 to 2,81 %, ash 4,39–3,96 % and nitrogen-free extractive substances 9,31–15,81 % in absolutely dry matter. The highest content of nutrients and metabolic energy is allocated to the breeds Belokokonnaya-2 (protein – 66,55 %, fat – 16,95 %, metabolic energy – 20,86 MJ/kg) and Kavkaz-2 (protein – 64,10 %, fat – 15,59 %, metabolic energy – 20,24 MJ/kg).