## 1 Introduction  
Phenolics consist of a broad range of secondary metabolites that are subdivided into different classes, including phenolic acids (hydroxybenzoic and hydroxycinnamic acid derivatives), flavonoids (flavonol, flavanol, isoflavoids, and anthocyanin), coumarins, lignans, and tannins(hydrolyizable and condensed tannins) [1; 2]. Phenolic compounds are an important group of secondary plant metabolites that have been shown to be responsible for many health benefits such as antimicrobial, antioxidant, anticancer, antidiabetic, and anti-inflammatory effects [3]. However, the phenolic compound contents and their pharmacological functions are vitally dependent on pre- and postharvest factors such as environmental and agronomic conditions, cultivar selection, stage of maturity, and extraction procedure [4]. Based on that, it is important to determine the optimal harvesting time for the highest amount of active ingredients (particularly phenolic acids and flavonoids) and maximum pharmacological activity [5; 6]. Plant maturity is the stage of development in crops where there are close relationships between plant features and their nutritive values. Plant maturation analysis may be used as a low-cost tool to analyze the nutritive composition of forages that provide relationships between nutritive value and suitable harvest time [7]. Additionally, forage maturity analysis is an important concept used to evaluate the yield and quality of the crop. Recently, [PERSON] et al. [8] studied the forage growth stage as one of the most important factors influencing nutritional composition. However, when a plant matures, the cytoplasmic compartment levels of the cells decrease and the quantities of proteins, lipids, soluble carbohydrates, and minerals are also reduced. In contrast, the dry matter (DM) content increases as the WCR crop matures. Therefore, the concentrations of phenolic acids and flavonoids in WCR may differ based on the different cultivar, environment, and stages of maturity [9]. Rice (_Oryza sativa_ L. Japonica) is an important food crop in South East Asian countries. Particularly in Korea and South Asia, rice is a community and a socioeconomic entity. Over the centuries, the Koreans have cultivated rice in hot and humid summer conditions. After harvesting the rice crop, the straw is used to feed ruminant animals, and the grains are consumed as a staple food. In addition, high-yield rice varieties are cultivated and these varieties greatly improve the agricultural inputs per acre yield of rice in the Korean peninsula [10]. The whole crop rice forage, including leaves, panicles, and stems, is harvested at different maturity stages, such as heading, milky, yellow-ripen, grain, and grain maturity, which are conditioned into whole-crop rice silage, hay, and hayalage development for feed for livestock animals. [PERSON] et al. [11] reported that whole crop rice silage (WCRS) prepared at the yellow-ripe stage contained approximately 6-7% crude protein (CP), which is similar to whole crop barley silage. In addition, WCRS usually contains a high amount of \(\alpha\)-tocopherol (lipid-soluble vitamins) at the yellow-ripe stage compared with the milky stage of WCR [12]. Many studies have also shown that the stage of maturity of crops may affect chemical compositions and fermentation profiles, as well as the net energy content of forages [7; 13]. The stage of maturation has a vital role in the nutritive value and ensiling process of the forage [14]. [PERSON] and [PERSON] [15] reported that whole crop wheat harvested at the flowering stage for silage had improved dietary fiber, digestibility, and milk quality and yields than other maturity stages. On the other hand, [PERSON] et al. [16] reported that the best harvest time for wheat silage was the grain stage in terms of the yield and nutrient composition. Based on the reports, the most suitable stage to harvest whole crop rice for ensiling and optimum phenolic and flavonoid profiles remains unclear [17].