Effect of compaction on nutritional quality and aerobic stability of silage corn after opening silos

Abstract: Compaction level is one of the major factors determining the nutritive value of silage. The low porosity of tightly compacted silage reduces O2 diffusion, thus limiting aerobic deterioration. If the silo is rapidly filled and densely packed with fresh forage, available O2 is quickly utilized and depleted by aerobic and facultative microorganisms as well as by the ensiling material through respiration with minimal loss of water soluble carbohydrates. Although compaction of the ensiled material is important, it is also necessary to seal silage quickly and carefully. The objective of this study was to evaluate the effect of different compaction levels on the nutritive value, fermentation characteristics, and aerobic stability of corn (Zea mays L. cv. Xinsiyu 10) silage so as to provide reference for establishing multiple linear regression models for silage production practice, as well as predict the silage quality quickly after the silos were opened according to the known conditions (opening time, compaction degree, temperature). The corn was sown on April 10, 2015 and harvested at the late milk stage (July 20, 101 d after planting). The corn was chopped into 1-2 cm segments in the field. The chopped corn was taken to the laboratory where mini-silos were filled and compacted. The mini-silos had a capacity of 30.2 L (height, 1020 mm; diameter, 194 mm). The corn was ensiled at 5 bulk densities (350, 400, 500, 600 and 700 kg/m3) and then fermented for 50 d. Silage samples were collected after 0, 12, 14, 36, 60 and 108 h after the silos were opened and then analyzed to determine pH value, dry matter, crude protein, neutral detergent fiber, acid detergent fiber, water soluble carbohydrates, lactic acid, acetic acid, and NH3-N, and the aerobic stability was evaluated by using an online multi-channel temperature recorder. Curve fitting between compaction and silage quality was performed, and multiple linear regression analysis between the silage quality and the silo opening time, compaction, and silage temperature was carried out. The results showed that dry matter and crude protein concentrations in the 350 kg/m3 treatment were respectively 2.6%-11.9% and 22.8%-37.0% lower than that in the 600 and 700 kg/m3 treatments (P<0.05); but neutral detergent fiber, acid detergent fiber, NH3-N concentrations and pH value in the 350 kg/m3 treatment were respectively 1.2%-4.6%, 6.2%-14.1%, 14.1%-37.4% and 3.1%-39.9% greater than that in the 500, 600 and 700 kg/m3 treatments (P<0.05). The increase of 2 ℃ above room temperature was considered a break of aerobic stability. The silage aerobic stability increased as silage density increased. The 600 kg/m3 treatment also showed the highest stability among the treatments (100 h in air; P<0.05). And the fitting degree of the multiple linear regression models between the above indices and the silo opening time, compaction, silage temperature reached 76.8%-92.3%, and the R2 reached 0.590-0.853. Among them, the model fitting degree and R2 of crude protein were the highest, and using this model to predict, the fitting degree was 92.3%. Therefore nutritive values and fermentation characteristics increased, and aerobic stability improved as silage compaction increased. In summary, 600 kg/m3 is the best density for producing corn silage with high fermentation quality and aerobic stability. This is of great significance to guide the production practice.