## 1 Introduction
In conclusion, silage VOCs can have negative, neutral, or positive effects on feed selection and intake by ruminants. The herbage utilization method affected the composition and sensory characteristics of milk and cheese, even when the forage's botanical composition and plot origin were the same. Therefore, the distinct flavor of silage has sparked growing interest in studying its chemical composition, driving further research into the VOCs that influence silage quality. In food flavor chemistry, gas chromatography-mass spectrometry (GC-MS) is commonly used to compare the retention index (RI) and odor characteristics of target compounds with those of control compounds (real compounds) [18]. This method provides an effective initial identification of compounds, enabling the identification or extraction of target compounds from complex mixtures [19]. Gas chromatography-ion migration spectrometry (GC-IMS) [20] and electronic nose (E-nose) technology [21] have gained popularity in recent years due to their advantages of simple operation, high sensitivity (detecting compounds at the ppb level), and the ability to perform real-time and rapid analysis. The E-nose has a broad detection range and can detect and analyze various gases in real time. With the continuous advancement of identification technology, the accuracy of classifying different VOC gases has reached 97.5% [22]. Furthermore, these new applications continue to emerge and remain an attractive area of research, with significant utilization in various food studies [23], including tea flavors [24], evaluation of milk [25], investigation of meat [26], and assessment of fermented alcoholic beverages [27]. As small molecules, VOCs are the first to be perceived (by smell or taste) when silage is presented to animals. These compounds are produced, released, or retained from the feed substrate and play a role in stimulating the appetite of ruminants [28]. The type, concentration, and formation of VOCs are crucial for assessing odor characteristics, classification, and identification and guiding the production, processing, and utilization of raw materials [23]. However, current research on whole corn silage mainly focuses on its nutritional value, fermentation quality, and microbial content, with relatively little attention given to analyzing its overall characteristic odor. Therefore, utilizing various flavor-omic analytical instruments to study the aroma of silage samples allows for the extraction and detection of VOCs from different silage substrates, providing a more comprehensive dataset for understanding the odor profile of silage. This study employed advanced analytical methods to identify VOCs in silage, such as HS-SPME-GC-MS, HS-GC-IMS, and E-nose techniques. The objective was to analyze the differences between abnormal silage with a bitter almond taste and normal silage from the same silo and to trace the specific compounds responsible for this unique smell. While odor changes due to microbial activity or production techniques are inevitable, effective management can minimize these odors and enhance silage quality. The study aims to deepen the understanding of silage odor diversity, address challenges posed by VOCs, and develop management strategies to control them, ultimately improving silage quality and supporting the sustainable development of dairy farming.