Effect Of Compaction And Harvest Stage On Quality And Mycotoxin Of Whole-plant Corn Silage

Ensiled forage,particularly corn silage,is an important component of dairy cow diets worldwide.Forages can be contaminated with several mycotoxins in the field pre-harvest,during storage,or after ensiling during feed-out.Exposure to dietary mycotoxins adversely affects the performance and health of livestock and can compromise human health.Problems associated with mycotoxins in silage can be minimized by preventing fungal growth before and after ensiling.Therefore,the appropriate harvest stage is particularly important for controlling the level of mycotoxin contamination in feed.Maturity at harvest alters nutrient composition and ensiling potential of crops.As the corn crop maturity progresses,sugars in kernels are converted to starch and the dry matter content of kernels increases.How to balance the mycotoxin pollution with the best nutritional value and choose the suitable harvest stage is the key to corn silage preparation.At the same time,proper silage preparation methods,especially the control of compactness,is essential to reduce mycotoxin contamination of dairy cow feeds and certain mold-inhibiting chemical additives or microbial inoculants can also reduce the contamination levels.Objective: The purpose of this study was to select the suitable harvest stage and control the optimum level of compaction to modulate corn silage,so as to reveal the effects of compaction and harvest stage on the quality of corn silage and the changes of microbial community composition in fermentation and after silos opened,as well as the concentration changes of mycotoxins.At the same time,screening strains with the ability of degrading mycotoxin efficiently,exploring the optimum conditions for degrading mycotoxin,corresponding analysis with fermentation parameters of corn silage,further analyzing the change mechanism of mycotoxin concentrations in high-quality corn silage,so as to provide theoretical basis for balancing the contradiction between mycotoxin pollution risk and optimum nutritional value and selecting suitable harvest stage.Methods: In this experiment,Zea mays L.cv.Xinsiyu 10 was harvested at 1/2,2/3 and 3/4 milk line stages.The corn silage with 500 and 600 kg/m~3 compaction levels was fermented(90 d).The samples were collected and analyzed at fermentation stage(3,7,15,30,60 and 90 d)and after soils opened(48,96,144 and 192 h).The sensory evaluation of silage at the end of fermentation(90 d)was carried out.The fermentation characteristics(lactic acid,acetic acid,propionic acid,butyric acid,ammonia nitrogen),main nutrients(dry matter,crude protein,neutral detergent fiber,acid detergent fiber,starch,water soluble carbohydrate)were determined and analyzed.The relative feeding value on the silos opened(90 d)was calculated.The silage temperature was dynamically measured throughout the fermentation process.The aerobic stability after silos opened was determined.The dynamic changes of aflatoxin B1,zearalenone,deoxynivalenol,T-2 toxin and fumonisin B1 after fermentation and silos opened were rapidly and accurately monitored by ELISA.Microbial culture and macrogenomics techniques were used to analyze the dynamic changes of microbial flora and the growth and decline of microbial flora.The quality of corn silage was comprehensively evaluated by membership function method.Screening strains with high degradability of mycotoxin,defining their effective degrading components,determining the degrading efficiency of mycotoxin by mixing different concentration of lactic acid bacteria and yeast,using response surface methodology to explore the influence of mixed concentration of lactic acid bacteria and yeast,fermentation p H(p H=3.4,3.6,3.8)and temperature(28,33,38 ?)on the degrading efficiency of mycotoxin.The optimum degradation conditions obtained by screening were corresponded with fermentation parameters of corn silage,and the change mechanism of mycotoxin content in high quality corn silage was further analyzed.Results: 1)The dry matter concentrations of ensiling material in 2/3 and 3/4 milk line reached 32.74 and 35.16 respectively,while the starch concentrations was 30.30 and 35.06 respectively.The p H values of compaction 500 and 600 kg/m~3 of corn silage at 2/3 milk line decreased to 3.55 after fermentation 90 days.The concentrations of neutral detergent fiber and ammonia nitrogen in corn silage was the lowest and lactic acid was the highest before and after silos opened,while the concentrations of starch in corn silage with 600 kg/m~3 compaction was always higher at 3/4 milk stage.2)With the prolongation of harvest stage,the highest population of fungi and yeasts reached 5.56 and 6.98 lg cfu/g respectively,and the dominant fungi flora were transformed into yeast(42.25%)by community diversity analysis,while the highest concentrations of aflatoxin B1 was 5.46 ?g/kg.The contents of zearalenone,deoxynivalenol,T-2 toxin and fumonisin B1 were the lowest(4.34,34.24,7.17 and 131.53 ?g/kg).The population of mould in corn silage harvested and produced at the milk line of 2/3 before and after silos opened was the lowest at the compaction level of 600 kg/m~3.3)The comprehensive scores of nutrition,fermentation quality and mycotoxin concentrations(0.979)were the highest and aerobic stability was the best(182.03 h)before(0.85)and after(0.79)silos opened of corn silage with a compaction level of 600 kg/m~3 harvested at 2/3 milk line.4)Lactobacillus strain ZB18042-3 and yeast strain YT01-4 were screened for the highest degradation efficiency of mycotoxin.Lactobacillus thallus and supernatant have the ability to degrade mycotoxin,but the degrading rate of supernatant for mycotoxin is higher.The main effective component of yeast degrading mycotoxin is thallus.The degradation rate of zearalenone,deoxynivalenol and T-2 toxin was the highest when the concentrations of lactic acid bacteria was 7 lg cfu/g and yeast was 5 lg cfu/g,while that of aflatoxin B1 was the highest when the concentration of lactic acid bacteria was 8 lg cfu/g and the concentration of yeast was 4 lg cfu/g;that of fumonisin B1 was the highest when the concentrations of lactic acid bacteria was 8 lg cfu/g and the concentrations of yeast was 5 lg cfu/g.5)The optimum conditions for mycotoxin degradation were as follows: temperature was 36.66 ?,p H was 3.66,lactic acid bacteria concentrations was 7.36 lg cfu/g and yeast concentrations 4.84 lg cfu/g.The correlation coefficient between the conditions and fermentation parameters of corn silage treatment with the compaction of 600 kg/m~3 at 2/3 milk stage was the highest(0.997 and 0.995,P < 0.01).Conclusion: The prolongation of harvest stage to 2/3 milk line is helpful to improve the nutritional quality of ensiling material,and the increase of silage compaction can guarantee the fermentation quality of corn silage;it has an excellent effect on improving sensory characteristics,improving nutrition and fermentation quality,reducing the population of harmful microorganisms and reducing mycotoxin residues;it can enhance the aerobic stability of corn silage after silos opened,which is of great significance for reducing nutrient loss.The compaction of 600 kg/m~3 corn silage at 2/3 milk line during the whole fermentation process and after silos opened,the fermentation parameters can not only improve the fermentation quality of corn silage,but also have the optimum conditions for degrading mycotoxin,so it is the best treatment in fermentation quality,and the concentrations of mycotoxin is relatively low.