Effect Of Replacing Soybean Protein In Feed With Animal By-Product Meals In Silkworm Rearing On The Structure And Property Of Silk

As labor costs rise and the area planted with mulberry trees decreases,the traditional mulberry sericulture industry has been greatly challenged.Factory farming has many advantages and is an important development direction for the future of sericulture.However,there are still a number of problems facing the factory-fed sericulture industry,such as the high cost of raising silkworms(mainly feed).As the main source of protein for silkworms,the soybean protein content of artificial feed for silkworms accounts for30%to 50%of the feed quality,but China’s soybean production is insufficient,and to meet the needs of the feed industry,a large amount of soybeans need to be imported each year.Therefore,it is imperative to find new and economical protein sources for silkworm artificial feed.In this study,three animal by-products,keratin meal,meat and bone meal and poultry by-product,commonly used in the livestock and wool textile industries,were used as protein sources to replace soybean protein meal in the artificial feed of silkworm,to investigate their effects on the growth and silk structure and performance of silkworm,and to investigate the optimal ratio of the three animal by-products to replace soybean protein meal.The findings of this study are as follows:(1)The experiment of replacing soybean protein with wool keratin showed that the same molecular weight of wool keratin(5×10~2 Da)replaced different proportions of soybean protein in sericulture,and the increase in the proportion of keratin replacement led to a gradual decrease in body weight,cocoon volume and cocoon layer volume of mature silkworms,but the cocoon layer rate and mechanical properties of silkworms in the replacement group increased.The average increase in cocoon layer rate in the substitution group was 8.97 percentage points,and the maximum increase in break strength and elongation at break in the experimental group was 8.15%and 4.49percentage points compared to the control group(2.5%substitution group),while the change in silk fineness was not significant at substitution rates≤5.0%.Further study of the secondary structure and crystallinity of silk showed that the basic structure of silk did not change in the substitution group,but the relative crystallinity increased;the molecular weight of wool keratin had no significant effect(P>0.05)on the weight of mature silkworms,cocoon layer volume,silk mechanical properties and secondary structure.In a comprehensive analysis,the use of wool keratin to replace≤5%of soy protein in factory feed for silkworm farming has good feasibility.(2)The experiment of replacing different proportions of soy protein powder with meat and bone meal for silkworm rearing showed that with the increase of meat and bone meal replacement amount,the mature silkworm body weight,cocoon width,total cocoon weight,cocoon shell weight,and cocoon shell rate increase first and then decrease,reaching the maximum when the replacement proportion of meat and bone meal is 10%,and still reaching the right proportion level when the replacement proportion is 25%.With the increase of meat and bone meal substitution,the breaking strength of degummed silk increased first and then decreased,and the breaking strength increased up to 10.94%when the meat and bone meal substitution ratio was 15%,and the breaking strength still reached the proportional level when the substitution ratio was 50%.The effect of meat and bone meal substitution on silk’s secondary structure and crystallinity was further investigated.The results showed that the basic structure of silk did not change in the substitution group,but when the substitution amount was≤50%,the relative content ofβ-fold structure and crystallinity of the substitution group were increased compared with the control group,which indicated that substitution with meat and bone meal within a certain proportion of substitution could make the secondary structure of silk shift toβ-fold.In summary,it is considered that the optimum proportion of meat and bone meal to replace soy protein for sericulture is 10%.(3)Experiments with poultry by-product replacing different proportions of soy protein meal in silkworm farming have shown that with the increase of poultry by-product substitution ratio,the mature silkworm body weight,cocoon width,total cocoon weight,and cocoon shell weight increased first and then decreased.When the substitution ratio was 7.5%,it reached the maximum.When the substitution ratio was 15%,it could still reach the proportion level.With the increase of the substitution ratio of poultry by-product meal,the breaking strength of the degummed wire increased first and then decreased.When the substitution ratio was 7.5%,the breaking strength could be increased by 32.21%.When the substitution ratio was 25%,it could still reach the proportion level.The effect of poultry by-product meal substitution on silk’s secondary structure and crystallinity was further studied.The results showed that the basic structure of silk in the substitution group did not change,but when the substitution ratio was≤7.5%,compared with the control group,the relative content and crystallinity of theβ-sheet structure in the substitution group were improved,indicating that the substitution of poultry by-product meal in a certain proportion can make the secondary structure of silk change toβ-sheet.In summary,the best proportion of poultry by-product meal instead of soybean protein in silkworm rearing is 7.5%.