Constitute Variety and Nutrient Analysis of the Different Main Plant Parts of Caragana korshinskii for Animal Feed

Abstract

Caragana korshinskii, a protein-rich feed plant in arid regions, lacks comprehensive nutrient analysis. This study compared the chemical composition of its five parts (leaves, bark, twigs, branches, and stems) and evaluated protein quality through amino acid profiling and enzymatic digestion. Results showed that leaves and bark contained higher crude protein (16.6–18.6%) than stems (6.8%), with fiber components (NDF > 81% and ADF > 65%) contributing to structural rigidity. Aspartic acid dominated caragana proteins, while bark and twigs exhibited elevated proline levels. CNCPS analysis revealed leaves contained 53.3% intermediately degradable protein (PB₂) versus 11.6% non-protein nitrogen (PA), whereas bark and twigs had 38.8% and 45.8% PA, respectively. Despite higher PA content, bark and twigs demonstrated superior in vitro protein digestibility (73.2% and 67.4%) compared to leaves (61.2%). The findings established baseline nutritional data, highlighting part-specific variations in protein characteristics critical for optimizing caragana’s application in animal feed technology within resource-limited ecosystems.

1. Introduction

Animal-derived foods, including livestock products, are widely regarded as critical sources of high-quality protein and essential nutrients for humans in the contemporary era, as they enhance the bioavailability of numerous beneficial nutrients. In recent decades, the global livestock industry has experienced rapid growth to satisfy the increasing demand for meat and dairy products. However, the issue of livestock feed shortages, particularly concerning protein-rich feed, has become increasingly pronounced [1,2]. For instance, Europe’s livestock sector relies heavily on imported soybeans and soybean meal as primary protein-rich feeds [3]. Beyond protein feed shortages, the livestock industry also faces constraints from seasonal pasture scarcity. In northern China, for instance, the total grassland area spans approximately 2.8 × 10⁶ km² [4]. Geographic and climatic constraints limit grazing periods and reduce livestock carrying capacity. Consequently, research focus has shifted toward evaluating non-conventional plant feedstuffs, particularly abundant forest-derived protein sources [5,6].

Caragana korshinskii, a traditional and significant forest plant, is a perennial deciduous shrub that is extensively distributed across arid and semiarid regions of Eurasia. It was initially introduced as a resilient vegetation to combat desertification and soil erosion [7,8]. This hardy forest plant also serves as a crucial source of roughage in these challenging regions, with a long-standing history of utilization [9]. Notably, caragana shrub grasslands are recognized as effective unconventional feed resources for grazing livestock during the winter and spring months when other forage becomes scarce [10,11]. Caragana is typically harvested every three years to promote its growth, resulting in the production of substantial biomass, exceeding 4 million tons annually across China [7,9]. For a long time, caragana has been conventionally used as a valuable protein source for animal feed or for incorporation into ruminant diets, mainly by use of leaves and branches [12]. When a specific proportion of caragana powder is incorporated into the diet of dairy cows, it can lead to approximately at least a 10% reduction in grain consumption rates and a 20% decrease in production costs, while also resulting in a notable increase in milk yield [13]. Caragana powder is rich in nutrients and particularly beneficial for the fattening of livestock, such as cattle and sheep. Its inclusion promotes rapid growth and development, significantly shortening the fattening period [14,15]. However, the nutrient composition of caragana is still undisclosed and obscure, especially with respect to main different plant parts, which is absolutely the most fundamental information and essential data to the effective utilization of this plant resource for animal feeds.

While caragana is empirically used as feed, critical knowledge gaps persist regarding its part-specific nutrient partitioning and protein functionality. We hypothesize that (1) morphologically distinct plant parts (leaves, bark, twigs, branches, and stems) exhibit significant divergence in protein fractions and fiber architecture, and (2) these structural variations dictate differential protein digestibility, potentially contradicting conventional protein-quality paradigms.

To address these hypotheses and bridge the research gap, this study aims to (1) quantitatively profile the nutrient matrix of five caragana parts using CNCPS fractionation—a novel application for this species, and (2) decipher the relationship between protein subfractions and in vitro digestibility.

Considering the variability in nutrient characteristics, such as fiber content, protein content, and amino acid composition, the main plant parts of fresh caragana are categorized into leaves, bark, fresh twigs, branches, and skinless stems. The Cornell Net Carbohydrate and Protein System (CNCPS) is employed to further evaluate and analyze the protein fractions of each caragana component. Subsequently, in vitro simulated digestion experiments are conducted to assess the nutritional value. This research provides direction and guidance for the subsequent valorization and refining process of caragana as an abundant and sustainable feed resource for livestock.

2. Materials and Methods

2.1. Raw Material Collection and Preparation

Sixty 3-year-old Caragana korshinskii plants were randomly selected in 2023 from a farm in Kaiyuan County (42.53° N, 124.03° E), Liaoning Province, China, with climatic data (temperature and precipitation) for the three years prior to harvest detailed in Table S1. Using pruning shears, intact plants were cut at the root collar, with 5 representative branches collected per plant (total n = 300 branches). Each branch was separated into five morphological parts: leaves, bark, fresh twigs, branches, and stems (without bark). Then, we performed natural air-drying and grinding to 40–80 mm particles.

2.2. Nutrient Analysis

Five parts of each caragana sample were analyzed for ash (method 942.05), crude protein (CP method 976.06), and crude fat (CF method 991.36) contents following the Association of Official Analytical Chemists [16]. Neutral detergent fiber (NDF) content was determined by the UNE EN ISO 16,472 method [17] with the use of an alpha amylase and sodium sulfite and was expressed free of ash. Acid detergent fiber (ADF) and acid detergent lignin (ADL), expressed exclusive of residual ash, were determined by AOAC method 973.18. Neutral detergent insoluble protein (NDICP) and acid detergent insoluble protein (ADICP) were determined by analyzing the NDF and ADF residues, respectively, for Kjeldahl nitrogen. The fiber composition (cellulose and hemicellulose) was determined according to the National Renewable Energy Laboratory (NREL) standard analysis protocol [18]. Non-protein nitrogen (NPN) and soluble protein (SP) were quantified in accordance with the methodology established by G. Licitra et al. [19].

2.3. Protein Fractions in CNCPS

Protein fractions were estimated according to the Cornell Net Carbohydrate and Protein System (CNCPS) modified according to Licitra et al. [19]. Proteins were fractionated using the CNCPS system into three major fractions: NPN (PA), true protein (PB), and unavailable nitrogen (PC). Then, based on the inherent rates of ruminal degradation, fraction PB was fractionated into subfractions PB₁ (true soluble protein), PB₂ (protein insoluble in buffer and soluble in neutral detergent), and PB₃ (protein insoluble in neutral detergent but soluble in acid detergent) [20]. The calculation formulas for the protein fractions are as follows:

PA(%CP) = NPN(%SP) × 0.01 × SP(%CP)

PA(%CP) = NPN(%SP) × 0.01 × SP(%CP)

PB₁(%CP) = SP(%CP) − PA(%CP)

PB₂(%CP) = 100 − PA(%CP) − PB₁(%CP) − PB₃(%CP) − PC(%CP)

PB₃(%CP) = NDICP(%CP) − ADICP(%CP)

PC(%CP) = ADICP(%DM) × 100/CP(%DM)

2.4. Determination of Amino Acid Content

The amino acid contents of the samples were determined using an amino acid analyzer (Hitachi-LA8080, Hitachi City, Japan), following the AOAC Official Method 994.12 for sample hydrolysis and analysis. A total of ten milliliters of 6 N hydrochloric acid containing 0.1% phenol was employed to dilute the samples, which were then hydrolyzed under reflux at 110 °C for 24 h. After cooling each hydrolysate sample to room temperature, 20 mL of Norleucine Standard Solution was added using a volumetric pipette. The hydrolysates were filtered through a sintered glass filter and subsequently transferred into 1000 mL evaporating flasks. Following removal from the evaporator, each flask received an addition of 50 mL of sodium citrate buffer before being transferred to a 50 mL polyethylene bottle. The filtrate obtained from the hydrolysate samples was further filtered through a sintered glass filter into a 250 mL vacuum flask and then transferred into a separate beaker. Neutralization of the hydrolysates was achieved by adding 40 mL of NaOH (7.5 M) and adjusting the pH to approximately 2.2 with concentrated NaOH (2 M). For sampling purposes, aliquots diluted with sodium citrate buffer had their pH adjusted to exactly 2 using additional NaOH (2 M). The neutralized hydrolysate aliquots were further diluted with water, as necessary. Finally, after passing through a filter with a pore size of 0.2 mm, an analysis on an amino acid analyzer was conducted on a volume of filtrate measuring 20 mL.

2.5. In Vitro Protein Simulation Digestion

The in vitro digestion of caragana was slightly modified according to the method of Marambe et al. [21].

Simulated gastric digestion: The caragana sample (1 g) was incubated with 0.2% NaCl (25 mL) in a 50 mL Erlenmeyer flask for 10 min at 40 °C in a shaking water bath. The solution was brought to pH 2.0 ± 0.1 with 1 M HCl. Pepsin was added into this solution to result in a pepsin/protein ratio (E/S) of 1:250 w/w, and the mixture was subsequently incubated in a shaking water bath (150 rpm) at 40 °C for 2 h. The gastric digestion phase was terminated by inactivating pepsin by raising the pH of the solution to 6.8 with the addition of 1 M NaOH. After filtration, the residual protein content in the residue was determined for Kjeldahl nitrogen.

Simulated intestinal digestion: The caragana and gastric phase digested sample (pH 6.8) was incubated with 35 mL of SIFc (Simulated Intestinal Control Solution, 0.68% (w/v) KH₂PO₄ and 0.062% (w/v) NaOH in deionized water) and incubated for 5 min at 40 °C in a shaking water bath. To this mixture, 4 mL of SIF (Simulated Intestinal Fluid) containing pancreatin (E/S; 1:25 w/w) was added and incubated (150 rpm) for 4 h at 40 °C while mixing. After filtration, the residual protein content in the residue was determined for Kjeldahl nitrogen.

2.6. Data Analysis

All experiments were conducted with three independent technical replicates, with data presented as mean ± standard deviation (SD). Statistical significance was determined using one-way analysis of variance (ANOVA) followed by Tukey’s honestly significant difference (HSD) post hoc test for multiple comparisons in SPSS 24.0 (IBM Corporation, Chicago, IL, USA), adopting p < 0.05 as the significance threshold. Data normality and homogeneity of variances were verified by the Shapiro–Wilk test (p > 0.05) and Levene’s test (p > 0.10), respectively.

3. Results

3.1. Variety in the Main Different Plant Parts

Chemical composition is a critical factor influencing the nutritional value, digestibility, and processing properties of plant feeds, and protein and fiber contents are essential quality characteristics in forage. As indicated in

Table 1. Chemical composition of five parts of caragana (% DM).

Item	Leaf	Bark	Fresh Twigs	Branch	Stem
Ash	11.2 ± 0.1 a	4.2 ± 0.0 b	3.2 ± 0.2 c	2.1 ± 0.0 d	1.0 ± 0.0 e
CP	18.6 ± 0.1 a	16.6 ± 0.2 b	11.2 ± 0.0 c	6.8 ± 0.1 d	3.4 ± 0.0 e
NPN	2.2 ± 0.2 c	6.4 ± 0.3 a	5.1 ± 0.1 b	1.9 ± 0.2 c	1.0 ± 0.1 d
SP	4.9 ± 0.3 b	6.9 ± 0.0 a	6.1 ± 0.3 a	2.5 ± 0.3 c	1.2 ± 0.1 d
CF	10.5 ± 0.2 a	7.1 ± 0.1 b	5.9 ± 0.1 c	5.8 ± 0.2 c	7.1 ± 0.2 b
NDF	38.2 ± 0.4 e	54.5 ± 0.2 d	70.5 ± 0.1 c	80.5 ± 0.5 b	81.9 ± 0.3 a
ADF	34.8 ± 0.5 d	44.5 ± 0.9 c	58.7 ± 0.6 b	65.0 ± 0.1 a	65.0 ± 1.0 a
NDICP	3.8 ± 0.1 a	3.3 ± 0.0 b	2.2 ± 0.0 c	2.3 ± 0.1 c	1.3 ± 0.1 d
ADICP	3.5 ± 0.2 a	1.3 ± 0.0 bc	1.4 ± 0.3 bc	1.9 ± 0.0 b	0.8 ± 0.0 c
Cellulose	22.0 ± 0.2 e	35.2 ± 0.1 b	33.6 ± 0.2 c	32.8 ± 0.1 d	43.9 ± 0.2 a
Hemicellulose	15.2 ± 0.4 d	19.4 ± 0.0 b	20.4 ± 0.3 b	16.8 ± 0.8 c	22.2 ± 0.1 a
ADL	22.0 ± 1.8 b	15.4 ± 0.5 c	21.5 ± 0.1 b	27.6 ± 0.5 a	17.2 ± 0.9 c

CP, crude protein; NPN, non-protein nitrogen; SP, soluble protein; CF, crude fat; NDF, neutral detergent fiber; ADF, acid detergent fiber; NDICP, neutral detergent insoluble protein; ADICP, acid detergent insoluble protein; ADL, acid detergent lignin. Significant differences between plant parts within the same parameter are denoted by distinct superscript letters (a, b, c, d, e) in tables and figures, where means sharing no common letter differ significantly (p < 0.05).

, leaves exhibited the highest levels of ash, CP, and CF content (11.6%, 18.6%, and 10.5%, respectively) among the five parts. Additionally, bark ranked second in both CP and CF content, at 16.6% and 7.7%, respectively. Further analysis of protein characteristics revealed that bark had the highest content of SP and NPN, indicating more digestible protein. In summary, the CP content of leaves, fresh twigs, and bark constituted over 10% of the total dry matter of caragana plants. Additionally, leaves exhibited distinct differences in terms of fiber-related indexes. The NDF and ADF levels in leaves, measured at 38.2% and 34.8%, respectively, were significantly lower than those in other parts. Branches and stems exhibited nearly double the NDF and ADF contents, at approximately 80% and 65%, respectively. For cellulose and hemicellulose contents, most parts of the plant exhibited similar profiles, except for leaves and stems, which had 43.9% cellulose and 22.2% hemicellulose, while leaves had only 22.0% and 15.2%, respectively.

3.2. Protein Fraction Analysis and Comparison in Different Plant Parts

The PA and PB₁ fractions constitute the soluble protein fraction of feed, whereas the PB₂, PB₃, and PC fractions are classified as insoluble protein fractions. As shown in Figure 1, CNCPS analysis indicated high levels of the PA fraction (NPN content) in both caragana bark (39% of CP) and twigs (46% of CP). The soluble protein fraction in caragana leaves was 26.5%, while the insoluble protein fraction constituted 73.5%.

3.3. Amino Acid Composition in Different Plant Parts

The nutritional quality of protein is primarily determined by its amino acid (AA) profile. AAs, as reliable indicators of nutritional value, are considered essential for the survival, growth, and reproductive development of ruminant livestock. According to the data in

Table 2. Amino acid content of caragana.

Amino Acid Composition (mg/g DM)	Leaf	Bark	Fresh Twigs	Branch	Stem
Alanine	7.5 ± 0.2 a	2.9 ± 0.2 b	2.2 ± 0.2 c	0.8 ± 0.2 d	0.6 ± 0.0 d
Arginine	7.6 ± 0.1 a	2.6 ± 0.1 b	2.2 ± 0.0 c	0.9 ± 0.0 d	0.4 ± 0.0 e
Aspartic acid	26.3 ± 0.3 a	17.2 ± 0.7 c	23.8 ± 0.4 b	3.2 ± 0.3 d	1.7 ± 0.1 e
Cysteine	1.2 ± 0.0 a	0.7 ± 0.0 b	0.7 ± 0.0 b	0.3 ± 0.0 c	0.1 ± 0.0 d
Glutamic acid	19.2 ± 0.4 a	7.2 ± 0.2 b	5.6 ± 0.3 c	2.3 ± 0.1 d	1.3 ± 0.1 e
Glycine	9.0 ± 0.1 a	3.2 ± 0.1 b	2.4 ± 0.0 c	1.1 ± 0.1 d	0.7 ± 0.1 e
Histidine	3.7 ± 0.1 a	2.5 ± 0.2 b	1.5 ± 0.2 c	0.6 ± 0.0 d	0.4 ± 0.0 d
Isoleucine	8.3 ± 0.5 a	4.1 ± 0.3 b	2.8 ± 0.1 c	1.1 ± 0.1 d	0.6 ± 0.0 d
Leucine *	12.3 ± 0.2 a	5.3 ± 0.1 b	3.6 ± 0.1 c	1.4 ± 0.3 d	0.9 ± 0.2 e
Lysine *	9.5 ± 0.4 a	5.4 ± 0.3 b	3.3 ± 0.2 c	1.3 ± 0.0 d	0.8 ± 0.1 d
Methionine *	2.9 ± 0.0 a	1.1 ± 0.1 b	0.9 ± 0.1 b	0.4 ± 0.1 c	0.1 ± 0.0 d
Phenylalanine *	11.1 ± 0.2 a	4.1 ± 0.2 b	3.0 ± 0.3 c	1.2 ± 0.2 d	0.7 ± 0.1 d
Proline	5.6 ± 0.7 b	16.8 ± 0.4 a	17.1 ± 0.2 a	2.8 ± 0.0 c	1.4 ± 0.2 d
Serine	8.4 ± 0.0 a	4.2 ± 0.6 b	3.3 ± 0.0 b	1.1 ± 0.0 c	0.8 ± 0.1 c
Threonine *	8.4 ± 0.1 a	5.6 ± 0.5 b	3.2 ± 0.1 c	1.3 ± 0.1 d	0.8 ± 0.0 d
Tyrosine	8.7 ± 0.4 a	5.4 ± 0.0 b	2.8 ± 0.4 c	1.1 ± 0.2 d	0.4 ± 0.0 d
Valine *	11.1 ± 0.1 a	6.4 ± 0.3 b	4.3 ± 0.1 c	1.7 ± 0.1 d	0.8 ± 0.1 e

* Means essential amino acid. Significant differences between plant parts within the same parameter are denoted by distinct superscript letters (a, b, c, d, e) in tables and figures, where means sharing no common letter differ significantly (p < 0.05).

, 17 AAs were detectable, and their distribution patterns were consistent across different parts of caragana. Here, aspartic acid presented the highest level among the AAs, constituting 16.2% of the crude protein in leaves. The second highest was glutamic acid in the leaves, accounting for 10.4% of the total crude protein content. In caragana leaves, essential amino acids constituted approximately 30% of the total crude protein content, with higher levels of leucine, phenylalanine, and valine, while methionine was present in lower amounts.

3.4. In Vitro Digestibility of Protein from Different Plant Parts

The protein digestibility of various parts of the caragana plant was evaluated using in vitro simulations of gastric, intestinal, and gastrointestinal digestion. Figure 2a indicates that the digestibility of caragana leaf protein was relatively lower in single protease digestion, with 49.1% gastric digestibility and 44.4% intestinal digestibility. Contrary to general understanding, bark protein exhibited the highest digestibility rates, with 68.8% gastric digestibility and 64.8% intestinal digestibility. Even when considering total digestibility during two-step digestion involving pepsin and trypsin, leaves demonstrated 61.2%, while bark and twigs exhibited 73.2% and 67.4%, respectively. Figure 2b indicates the proportion of digestible protein to dry matter in various parts of caragana. In terms of the dry matter proportion, notably, caragana leaves and bark exhibited the highest levels of digestible protein content, with total digestible protein percentages of 11.4% and 12.1%, respectively.

4. Discussion

Chemical composition is a critical factor influencing the nutritional value, digestibility, and processing properties of plant feeds, and protein and fiber contents are essential quality characteristics in forage. A comparison with other forage grasses indicated that caragana leaves and bark contained significantly higher CP than Festuca sinensis (8.1%), tall fescue (9.8%), and old awned wheat (9.3%) [22,23]. Even fresh twigs also exhibited some advantages in terms of CP. Additionally, the NDF and ADF contents in caragana leaves were slightly lower than those in fescue triticale leaves, which contained 40.9% NDF [24]. Excessive levels of ADF, NDF, and ADL negatively impacted feed quality by binding ADL to some proteins, thereby reducing available protein levels. These characteristics above constitute the logical reasons why caragana leaves, bark, and fresh twigs possess essential and attractive protein qualities for animal feed, in addition to some necessary and moderate fiber components. Regarding caragana sticks and branches, their polysaccharide-rich composition in cellulose and hemicellulose, combined with low CP content, inspires ideas and technological advancements in energy feed conversion, such as silage fermentation or effective pretreatment to break down the inert barriers of NDF and ADF, thereby facilitating easier animal digestion and nutrient absorption, including fermentable sugars, organic acids, and microbial protein [25,26].

Caragana feed materials serve primarily ruminant animals in arid and semi-arid regions. The nutritional value of crude protein (CP) in ruminant feeds is influenced by both the rate and extent of rumen degradation, as well as the intestinal digestibility of rumen-undegraded protein (RUP) [27]. The CNCPS system is a widely utilized dynamic evaluation framework for estimating and assessing the degradation characteristics of feed proteins in the rumen. This system accurately reflects the digestion and utilization of forage by ruminants through its detailed categorization of proteins. Considering the soluble protein content in CP, caragana leaves (26.5%) presented a higher level than that of distiller grain (15.6%) and palm kernel cake (20.2%) [27]. The PA fraction particularly indicates the quantity of protein accessible to rumen microorganisms during the initial phase of feed protein degradation [28,29]. The rumen microbiota rapidly utilizes PA, thereby facilitating the synthesis of microbial proteins and cells in the animal’s intestinal system [29]. It is evident that the bark and twigs exhibited higher soluble protein content and lower insoluble protein content, with PA (the non-protein nitrogen fraction) constituting the largest proportion of the crude protein, which facilitated easier digestion and absorption of proteins from bark and twigs by ruminants. Soluble true protein (PB₁) in forages constituted a minor fraction of the total nitrogen content. Except for oat and peanut meal, the soluble true protein content in most feedstuffs is less than 10% of their total nitrogen [30]. In caragana leaves, PB₁ constituted 14.9% of the total crude protein content. In contrast, the PB₁ fraction in caragana bark, twigs, branches, and sticks accounted for 3.1%, 8.8%, 6.5%, and 6.5%, respectively. The PB₂ fraction varied significantly across different feed types, ranging from 23% in oilseeds to as high as 86% in soybean meal, and this proportion was even lower in silage. In comparison to these forages, data from various parts of caragana revealed that the PB₂ fraction was highest in leaves (53.3%) and relatively lower in other parts. The content of the PC fraction in soybean feed was approximately 8%, whereas in forage, it ranged from 11% to 21% [31]. The PC content across different parts of caragana varied between 8% and 27%, with higher concentrations of nondigestible proteins found in branches and sticks. The dry weight of branches and sticks constituted 65% of the total dry weight of caragana plants. Despite elevated levels of unavailable nitrogen, a substantial amount of crude protein remained available for further processing, such as silage fermentation and other applications.

Compared to other legumes and grasses [32,33], the amino acid content of caragana leaves exhibited similarities to white clover. Furthermore, the concentrations of aspartate and glutamate in caragana were higher than those in tall fescue, alfalfa, and other forage species. Proline levels were significantly higher in both bark and twigs. This discrepancy may be attributed to the specific growth and developmental characteristics inherent in caragana plants. The composition of essential amino acids was comparable to that in white clover (32.5%) [32]. Non-essential amino acids accounted for 56.9% of the total crude protein content; apart from cysteine and histidine, their distribution was generally more abundant on average. Current research indicates that certain non-essential amino acids play significant roles in various cellular functions, including gene expression, microRNA biogenesis, epigenetics, and T-cell activation and function. Furthermore, most non-essential amino acids are involved in cellular signal transduction and the regulation of nutrient metabolism via kinase pathways. For ruminants, non-essential amino acids are equally important for animal growth as essential amino acids. Limiting amino acids are defined as those with low ratios or amounts in essential amino acids required by animals. Typically, the limiting amino acids for ruminants include methionine, lysine, and threonine. In caragana plants, all parts were rich in lysine and threonine but comparatively lower in methionine. For instance, caragana leaves contained threonine and lysine at 8.44 mg/g and 9.54 mg/g, respectively, while methionine was present at only 2.94 mg/g. In summary, the amino acid profile of caragana seems relatively balanced and abundant, encompassing most of the essential amino acids required by ruminants. Additionally, caragana is rich in lysine and threonine, which could provide the limiting amino acids for ruminants. However, its methionine content is relatively low, which may necessitate the addition of exogenous methionine in caragana-based diets for ruminants.

The analysis of CNCPS protein fractions revealed that the non-protein nitrogen content in bark and twig PA fractions was higher than that in leaves, while the unavailable nitrogen fraction (PC) was lower compared to that in caragana leaves. The results from in vitro simulated digestibility were consistent with the CNCPS findings. Although the crude protein content in caragana leaves exceeded that in bark and twigs, the latter provided a greater amount of soluble protein with enhanced digestibility. In contrast, most proteins in bark and twigs existed as non-protein nitrogen, leading to higher digestibility in ruminants. Different parts exhibited distinct properties regarding digestion and absorption, thereby better addressing the varied nutritional needs of ruminants.

5. Conclusions

Through comprehensive detection and nutrient analysis for animal feed, five plant parts of Caragana korshinskii exhibited significant variations in crude protein, crude fat, and fiber contents and compositions. Leaves contained nearly 20% CP, with 53% medium-speed degrading protein and 26% aspartic acid composition, presenting a significant advantage in protein characteristics compared to common plants in arid and semi-arid regions. Stems and branches contained over 80% NDF and 65% ADF, compared with only 3%~7% CP, which were presumably characterized by their inert and protein-poor properties. Notably, the in vitro protein digestibility of bark and twigs appeared higher than that of leaves. Overall, crude protein, crude fat, and fiber accounted for over 60% of caragana and support its promising potential for animal feed. This work provided fundamental data and necessary information to understand the chemical structure and properties of caragana, thereby developing animal feed technology and applications.

However, this study has limitations that warrant consideration. First, our nutrient assessments were conducted under controlled in vitro conditions, which may not fully replicate complex ruminant digestive environments. Second, sampling was restricted to a single growth season and geographic region, potentially overlooking temporal and spatial variations in nutrient profiles. Future research should validate these findings through in vivo trials with target livestock, such as sheep and goats, evaluating actual nutrient absorption and metabolic responses; additionally, investigations into seasonal dynamics of bioactive compounds and their potential interactions with rumen microbiota are warranted.