## 4 Discussion
### Effect of Different Growth Stages on Nutritional Components of Whole-Plant Millet Silage
This complex interaction between growth stages and CP content highlights the dynamic nature of plant biochemistry in response to developmental changes. WSC is a digestible part of the feed that is directly proportional to the feed's digestibility and nutritional value. In this study, the WSC content gradually increased from the heading to the dough stages, reaching its peak at the dough stage and then is rapidly decreased by full maturity. This pattern is similar to [PERSON]'s [25] findings on the impact of irrigation on WSC content and grain yield in different wheat varieties, where the WSC content continuously increased from the jointing to flowering stages and then rapidly decreased during the grain-filling stage. The accumulation of WSCs is closely linked to photosynthesis, which accumulates WSCs through photosynthesis as the plant matures. In the later stages of growth, as light intensity decreases, the rate of photosynthesis drops, leading to a reduction in soluble sugar accumulation [26; 27]. Additionally, during the late growth stages, leaf senescence occurs, during which chlorophyll and other cellular components break down, releasing nitrogen and carbohydrates [28] and further contributing to the decline in WSC content as the growth period concludes. In this study, the numbers of LAB and the contents of LA and AA are significantly higher at the dough stage compared to the milk stage, while the number of general bacteria is significantly lower. LAB efficiently convert WSCs into organic acids such as LA and AA under anaerobic conditions, which helps lower the pH and inhibits the growth of harmful microbes. Lactic acid, in particular, is the most effective organic acid in reducing pH in the silage environment, being 10-12 times more acidic than other organic acids [29]. Additionally, as the growth stage progresses, the number of general bacteria initially increase and then decrease, peaking during the milk stage. These general bacteria compete with LAB for fermentation substrates, leading to energy losses in the silage [30]. Consequently, selecting a growth stage with appropriate DM content is crucial to control moisture and air in the silage, thus reducing the number of general bacteria and enhancing silage quality. The LA content typically increases with the WSC content. However, this correlation was not observed in Experiment 1. This discrepancy could be due to several factors. Variations in the types and activities of the microorganisms present can affect the fermentation process. Different strains of lactic acid bacteria may have varying efficiencies in converting WSCs to lactic acid. Temperature, pH, and moisture content can influence microbial activity and fermentation efficiency. Additionally, other nutrients essential for microbial growth and activity may be limited, affecting the overall fermentation process and the production of LA. The LA/AA ratio is commonly used as a qualitative indicator of fermentation and the aerobic stability of silage. A higher LA/AA ratio often indicates a more efficient fermentation process, as lactic acid is a stronger acid and more effective at lowering pH, which preserves the silage. A balanced or lower LA/AA ratio can improve the aerobic stability of silage. While lactic acid is important for initial preservation, AA plays a crucial role in inhibiting the growth of spoilage organisms when the silage is exposed to air. It is generally recommended that the concentration of AA should be around 3% DM [31]. [PERSON] et al. found that at low levels of AA (below 4.1% DM), nutritional losses can be highly variable [32]. [PERSON] et al. reported that adding 5% DM of AA to the daily diet of dairy cows resulted in lower feed intake within 4 h of the morning feeding, but no differences in intake were observed over the entire day. Additionally, the average milk yield and milk quality throughout the study period did not differ from the control group [33]. [PERSON] et al. indicated that the AA content required for successful silage preservation can be very high.