| Crop straw is an important agricultural resource with an annual output of approximately 800 million tons in China.During harvest season,large quantities of straws are burned,resulting in environmental pollution and wastage of agricultural resources.In order to effectively utilize the crop straw resources,we firstly investigated the quantities and types of crop straw resources in five provinces of central China;we then assessed the efficacy of three fermented crop straws(corn,wheat and rice)for mass rearing of the housefly Musca domestica by recording their biological traits.In addition,we analyzed and compared the nutritional components of M.domestica larvae fed with different straw diets.Finally,we examined the possibility of massed reared M.domestica fed with straw diet as feed for laying hens.Our study provided a feasible,cost-efficient and effective crop straw processing technique which could contribute to the sustainable use of agricultural resources.1.Investigation on species and quantities of crop straw resources in five provinces of central ChinaBased on China Statistical Yearbook of 2015,a straw coefficient method was used to evaluate the crop straw yields of five different provinces in central China(Hunan,Hubei,Henan,Jiangxi and Anhui).The results showed a total output of 214,831,400 tons in 2014,accounting for 27.36% of total output of the country.Henan province recorded the most abundant straws with 73,264,700 tons yearly.The main crop straws included rice,wheat,corn,bean,peanut and rapeseed and the yield was 83,119,000,60,336,900,27,998,900,4,574,400,8,094,000 and 21,418,800 tons,respectively.Rice straw was mainly distributed in Hunan,Hubei,Jiangxi and Anhui province and it was the most abundant in Hunan.Wheat straw was mainly present in Henan,Hubei and Anhui,being the most abundant in Henan.Corn straw was present in Henan,Hubei,Hunan and Anhui and Henan had the most abundant.Beans straw was mainly found in Anhui Province.All these five provinces have oil-crops straw but Hubei province had more than others.2.Screening of crop straw diets and assessment of the diets for rearing of M.domesticaTo offer new insights for sustainable utilization of crop straws,in this study,the artificial diets were formulated by fermenting corn,wheat and rice straw powder and then mixing them with wheat bran.The quality of the different straw diets were assessed by measuring the nutritional components after feeding M.domestica.The results suggested that:(1)The straws showed the highest nutritional value after a 3-day fermentation at 25?.(2)Based on the biological traits data(hatch rate,larval survival rate,pupation rate and emergence rate)collected on M.domestica,the corn straw diet seemed to be the best diets for rearing of M.domestica followed by wheat diet and then rice diet.The corn and wheat straw diets were thus chosen for the following experiments.(3)The corn straw diet showed significant decreases in crude protein and fat content post feeding by M.domestica,similar trends were also recorded in wheat straw diet with soluble sugar,starch,crude protein and crude fat contents.(4)In summary,we figured out an optimal procedure for preparing the artificial straw diets,as follows,the crop straws were processed by milling and sieved using 10-mesh sieve.The powder was then supplemented with 1% yeast and 5-6 times of water(W/W),fairly sealed and then fermented at 25? for 3 days.After fermentation,the substrate was mixed with bran at a ratio of 1:1(w:w)to get the straw artificial diets.The recommended rearing density was set up as: 200 mg M.domestica newly-hatched larvae per 250 g diet.3.Analysis of nutritional components of M.domestica reared on corn and wheat straw dietsInsect powder was made from M.domestica larvae that were previously fed with corn and wheat straw diets and the nutritional value of the powder was analyzed according to the National Food safety Standard.Our results revealed that:(1)There was no significant difference(P> 0.05)in the nutritional components(water,crude protein and fat,and ash contents)of M.domestica larvae fed on corn and wheat straw diets when compared to those fed with Conventional Diet(CD)(57.499%?57.802%?60.732% for corn straw,wheat straw and CD,respectively).This indicated that M.domestica can be used to transform and utilize crop straws;(2)Nine Essential Amino Acid(EAA)and Ten Non-Essential Amino Acid(NEAA)post-treatment were recorded on M.domestica larvae fed with the different straw diets.With respect to the protein quality,the criteria EAA/TAA(Essential Amino Acid/Total Amino Acid)ratio of 0.38,0.37 and 0.38 and EAA / NEAA(Essential Amino Acid/Total Amino Acid)ratio of 0.62,0.58 and 0.61 respectively recorded for corn,wheat and CD were similar to the FAO-based evaluation standard,suggesting that M.domestica larvae has a high protein quality.4.Utilization of straw diets fed M.domestica as a feed supplement for laying hensWe added 4g of powdered larvae into 100 g of laying hens basic diet and monitored their gowth and development.The results showed that:(1)The powder obtained from M.domestica larvae reared on corn straw,wheat straw and CD based diets increased the eggshell hardness by 18.05%,45.56% and 7.45% in the positive control and by 18.73%,46.40% and 8.07% in the negative control respectively.No significant differences were recored in hens weight,eggs laying potential,egg weight,egg white relative weight,egg yolk relative weight,egg shell relative weight and egg shape index;(2)The daily supplementation of powdered larvae into the food substantially increased the lysozyme activity(Lsz)of the positive and negative controls,CD,Corn and wheat straw diets by 139.65,166.24,317.46,387.24 and 324.26 U/ml,respectively and superoxide dismutase(SOD)activity of the positive and negative controls,CD,Corn and wheat straw diets by 311.00,385.06,361.74,394.48 and 339.64 U/ml,respectively in serum of laying hens whereas no significant difference was observed in Total Antioxydant Capacity(TAC)of the positive and negative controls,CD,Corn and wheat straw diets by 12.91,12.70,12.21,12.74,11.88 U/ml,respectively.In conclusion,we compared the efficacy of different crop straws on the rearing of M.domestica,and evaluated the differences of nutritional components of M.domestica larvae reared on corn and wheat straw diets,finally analyzed the effect of M.domestica larval powder on the growth and development of laying hens.We established a feasible,cost-efficient and effective crop straw pretreatment and insect-mediated transformation technique for utilization of crop straws by M.domestica.The optimal formula of crop straw diet for M.domestica and the recommended rearing density were obtained in present study.Our results provide the theoretical and practical basis for the comprehensive utilization of crop straw resources and the transformation of straws by insects. |
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