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Current IssueEditorial BoardOnline First ArticlesArchive

Full Research Article

Meta-analysis of the Effects of Chinese Herbal Additives on the Production Performance, Immune Function and Meat Quality of Sheep

Z
Zhina Du1,2,3
W
Wu Sun1,2,3,*
X
Xiayang Jin1,2,3
S
Shike Ma1,2,3
Y
Yuhong Ma1,2,3
1Academy of Animal Science and Veterinary Medicine, Qinghai University, Xining-810016, China.
2Key Laboratory of Livestock and Poultry Genetics and Breeding on the Qinghai-Tibet Plateau, Ministry of Agriculture and Rural Affairs, Xining-810016, China.
3Plateau Livestock Genetic Resources Protection and Innovative Utilization Key Laboratory of Qinghai Province, Xining-810016, China.

ABSTRACT

Background: This meta-analysis systematically evaluates the effects of Chinese herbal additives on production performance, immune function and meat quality in sheep to support their application in ruminant nutrition.

Methods: A total of 13 studies, comprising 37 controlled trials, were included in the analysis. The overall effect size was assessed by forest plots and meta-analysis was conducted to identify sources of heterogeneity, perform sensitivity analysis and evaluate publication bias by funnel plots.

Result: Dietary supplementation with Chinese herbal additives significantly increased average daily gain (ADG) and average daily feed intake (ADFI) (P<0.05) and reduced the feed-to-gain ratio (F/G) (P<0.05). Immunological analysis showed that serum IgA and IgM levels were elevated (P<0.05). For meat quality parameters, the additives increased cooking yield and pH (P<0.05) and decreased shear force (P<0.05) with no significant effect on drip loss (P>0.05). Funnel plot analysis revealed minimal publication bias and sensitivity analysis confirmed the robustness and reliability of the results. These findings suggested that Chinese herbal additives contributed to enhanced production performance, immune function and meat quality in sheep. Further research should validate these findings through more controlled feeding trials, while exploring the active ingredients and mechanisms of action of Chinese herbal additives.

INTRODUCTION

With the development of scale and industrialization of animal husbandry and the arrival of the era of comprehensive anti-antibiotic ban, seeking green, safe and effective feed additives has become the key to the development of the livestock industry. Chinese herbal medicines, with their natural properties, low toxicity, minimal side effects and multi-functionality, demonstrate significant potential in livestock and poultry breeding (Zhang et al., 2024). Numerous studies indicate that Chinese herbal additives have the advantages of promoting growth, enhancing immune function of the body and improving the quality of animal products (Liu et al., 2024; Wei, 2024; Zhang et al., 2024). Chen et al. (2021) reported that a Chinese herbal polysaccharide mixture (CMP), formulated with Lycium barbarum and Astragalus membranaceus at a 2:1 ratio, enhanced ADG and increased the serum concentrations of IgA, IgG and IgM. Additionally, CMP treatment elevated the relative abundance of Fibrobacteria, altered rumen microbial fermentation patterns, improved immune function and ultimately enhanced growth performance. Similarly, Ma et al. (2024) added different concentrations of salvia sclarea extract to the diet of 2-month-old Chinese Merino lambs and also arrived at the same conclusion. In sheep breeding production, Chinese herbal additives have shown many significant advantages, serving as an effective strategy to improve breeding efficiency. Research suggests that incorporating an appropriate amount of Chinese herbal additives into the diet of sheep can effectively improve the production performance of sheep. On the one hand, herbs can regulate the feed flavor, increase the feed intake, promote the digestion and absorption of nutrients, thus significantly increasing the daily weight gain and shortening the fattening cycle. On the other hand, by regulating the rumen development, it improves the feed digestive utilization and reduces the breeding costs (Du, 2023; Huang, 2023; Karnani Monika et al., 2020). Chinese herbal additives also exhibit unique immunomodulatory effects (Li et al., 2020). Many Chinese herbs are rich in polysaccharides, organic acids, alkaloids, volatile oils, anthracenes, etc. These substances can regulate the immune function of the animal body and promote the development of immune organs and enhance cellular immune response (He, 2016; Zhang et al., 2016). Herbs can significantly enhance the meat quality by enhancing meat tenderness, flavor and reducing fat content (Wang, 2016; Xia, 2022). At present, there have been many studies on the addition of Chinese herbal additives to sheep diets by domestic and foreign animal husbandry experts, but the quality of the studies varies and the experimental results have not yet been widely recognized due to the differences in feeding methods, raw material composition and processing methods (Zhang, 2023; Zhou et al., 2024).
               
Meta-analysis significantly enhances the credibility and generalizability of research by systematically integrating multiple independent studies, providing more reliable evidence for scientific decision-making. (Zhang et al., 2023). Meta-analysis was conducted on literature related to the production performance, immune function and meat quality of sheep with Chinese herbal additives from 2005 to 2022, screened from Chinese databases. The aim was to provide a statistical evaluation of these effects, offering a scientific basis for the rational application of Chinese herbal additives in sheep production.

MATERIALS AND METHODS

Literature search
 
A literature search was conducted in the China National knowledge infrastructure (CNKI), Wanfang Database, VIP database and Chinese science citation database (CSCD). Keywords included “Chinese herbal additives,” “sheep,” “production performance,” “immune function” and “meat quality.” Production performance indicators included average daily gain (ADG), average daily feed intake (ADFI) and feed-to-gain ratio (F/G); immune indicators included IgA, IgM and IgG levels; meat quality indicators included pH, drip loss, shear force and cooking yield. Studies from 2005 to 2022 were included in the search.
 
Literature screening
 
In this study, literature selection was conducted based on the following criteria: 1) Studies must include the effects of Chinese herbal additives on production performance, immune function and meat quality of sheep; 2) The results of the study must include the outcome indicators of production performance, such as ADG, ADFI and F/G, the outcome indicators of immune function, such as serum IgA, IgG and IgM levels and the outcome indicators of meat quality, such as pH, drip loss, shear force and cooking yield; 3) The study must have both a control group and an experimental group; 4) Studies must be published in Chinese. All retrieved literature was independently screened, extracted and reviewed by two researchers. A total of 50 papers were retrieved according to the rules of literature search, among which 37 duplicates, conference papers, conference abstracts and unpublished papers were excluded and 13 papers were finally included.
 
Data extraction and characteristics
 
This study selected 13 articles, encompassing 37 controlled trials based on experimental designs. The following data and information were extracted: article title, publication year, sample size, concentration of Chinese herbal additives in experimental diets, the experimental data and the standard deviation. When multiple studies shared the same publication year and author, they were distinguished using superscript numbers (1), (2), (3), (4). A total of 13 papers were included in this meta-analysis, including 16 ADG studies, 16 ADFI studies, 16 F/G studies, 11 IgA studies, 11 IgG studies, 11 IgM studies, 8 pH studies, 5 drip loss studies, 4 shear force studies and 10 cooking yield studies. All included studies were controlled trials involving Chinese herbal additives.
 
Statistical analysis
 
Because production performance, immune function and meat quality outcomes were continuous variables, we used the standardized mean difference (SMD) as the effect size metric (Zhang et al., 2023). In this study, the SMD method developed by Hedges et al. (1985) and Cohen (1988) was used to evaluate the effect of herbs on the feeding effects (production performance, immune function, meat quality) of sheep. We determined the 95% confidence interval (CI) for all measured parameters and reported their 95% CI values. Detailed procedures are described in the Appendix. Meta-analyses were performed using the Python throughout and effect sizes were pooled using the Cohen or Hedges method in the metacont command. In addition, this analysis was assessed using the I2 method for between-study heterogeneity. When I2<50%, inter-study heterogeneity was considered to be low or non-existent, the effect sizes were pooled using fixed-effects model; when I2>50%, high inter-study heterogeneity was considered to exist. The effect sizes were pooled using the random-effects model. When the 95% confidence interval of the SMD++ did not overlap zero, it was considered that the feed additive group had a significant effect on the production performance, immune function and meat quality outcome indicators of sheep relative to the control group. When the SMD++ was greater than 0, it was considered that the feed additive group had a positive effect on the variable, while the opposite indicated a negative effect. To ensure the authenticity and accuracy of this analysis, funnel plot was used for bias analysis of published articles. Sensitivity analysis was conducted using Leave-one-out analysis. Sensitivity analysis is usually carried out by excluding each study in turn, assessing the impact of that study on the pooled effect size and heterogeneity, then evaluating the stability of the results.

RESULTS AND DISCUSSION

Meta-analysis of Chinese herbal additives on production performance of sheep
 
The meta-analysis demonstrated that there was inter-study heterogeneity (P<0.01, I²>50%) in the quantitative changes in the outcome indicators of production performance represented by ADG, ADFI and F/G after the addition of Chinese herbal additives to the feed, so the random-effects model was applied to pool the effect sizes. The pooled effect sizes of ADG and ADFI were to the right of the null line and the pooled effect size of F/G was to the left of the null line, with none of them intersecting the null line (Fig 1a). The meta-analysis indicated that the addition of Chinese herbal additives to feed significantly increased ADG and ADFI (P<0.05) and significantly decreased F/G (P<0.05). Based on this meta-analysis, these findings suggest that Chinese herbal additives significantly improved the production performance of sheep.

Fig 1: Forest plot showing the effect of Chinese herbal additives on (1a) ADG, ADFI and F/G; (1b) serum IgA, IgG and IgM levels; (1c) cooking yield, pH, drip loss and shear force in sheep.


 
Meta-analysis of Chinese herbal additives on immune function of sheep
 
The meta-analysis showed that there was inter-study heterogeneity in the quantitative changes in the outcome indicators of immune function represented by serum IgA, IgG and IgM levels after the addition of Chinese herbal additives to the feed (P<0.01, I²>50%) and therefore the pooled effect sizes were analyzed using a random-effects model. The pooled effect sizes for IgA and IgM were to the right of the null line and the pooled effect size for IgG was to the left of the null line, with none of them overlapping the null line (Fig 1b). Thus, the meta-analysis indicated that the addition of Chinese herbal additives to feed significantly increased serum IgA and IgM levels (P<0.05) and significantly decreased IgG levels (P<0.05). Based on this meta-analysis, these results suggest that Chinese herbal additives can significantly enhance the immune function of sheep.

Meta-analysis of Chinese herbal additives on meat quality of sheep
 
The meta-analysis showed that there was inter-study heterogeneity (P<0.01, I²>50%) in the quantitative changes of meat quality outcome indicators represented by cooking yield, drip loss, shear force and pH after the addition of Chinese herbal additives to the feed, so the random-effects model was applied to pool the effect sizes. The pooled effect sizes of cooking yield and pH were to the right of the null line and the pooled effect size of shear force was to the left of the null line, with none of them intersecting the null line (Fig 1c). Thus, the meta-analysis indicated that the addition of Chinese herbal additives to feed significantly increased cooking yield and pH (P<0.05) and significantly decreased shear force (P<0.05), indicating improved meat tenderness, but had no significant effect on drip loss (P>0.05). Based on this meta-analysis, these results suggest that Chinese herbal additives could significantly improve the meat quality of sheep.
 
Sensitivity analyses
 
Chinese herbal additives significantly influenced sheep production performance, immune function and meat quality. This meta-analysis revealed substantial heterogeneity (P<0.01, I²>50%). These variations may relate to differences in sheep breeds, herbal additive compositions and inclusion rates, basal diets and farm management practices. We conducted sensitivity analyses to evaluate result stability and credibility (Table 1). After sequentially excluding each included study, the pooled effect sizes of the remaining studies were distributed on both sides of the null line without overlapping it, further supporting the accuracy of the findings (Fig 2).

Table 1: Results of meta-analysis of the effects of Chinese herbal additives on production performance, immunity function and meat quality of sheep.




Fig 2: Sensitivity analysis showing the effect of Chinese herbal additives on (2a) ADG, ADFI and F/G; (2b) serum IgA, IgG and IgM levels; (2c) cooking yield, pH, drip loss and shear force in sheep.


 
Bias analysis
 
The studies on production performance, meat quality and immune function outcome indicators were predominantly concentrated in the middle and upper regions of the funnel plot and demonstrated good symmetry (Fig 3). This distribution pattern indicated that the sample size of this meta-analysis was sufficient and representative, the experimental precision was high and the data were reliable. However, several studies were located in the outer regions of the funnel plot, suggesting the presence of some publication bias in this study.

Fig 3: Funnel plot showing publication bias in the effect of Chinese herbal additives on (3a) ADG, ADFI and F/G; (3b) serum IgA, IgG and IgM levels; (3c) cooking yield, pH, drip loss and shear force in sheep.


 
Effect of Chinese herbal additives on the production performance of sheep
 
Chinese herbal medicine can optimize intestinal development and flora, enhance digestive function and improve production performance (Li et al., 2024; Shao et al., 2025). The meta-analysis results demonstrated that the inclusion of Chinese herbal additives in diets led to significant increases in ADG and ADFI, accompanied by a significant decrease in F/G. These findings are consistent with previous studies by Liang et al. (2013). Chinese herbs, containing rich nutrients such as alkaloids, organic acids, trace elements and digestive enzymes, not only provide essential nutrients for growth and development but also promote feed nutrient decomposition, thereby enhancing production performance (Feng et al., 2024). Bao et al. (2019) found that astragalus polysaccharide could significantly increase Tibetan sheep’s ADG and ADFI and decrease F/G. This effect is probably attributable to its polyphenols’ ability to regulate rumen micro-ecological balance, promote the growth of beneficial bacteria and enhance beneficial bacteria activity, ultimately improving the production performance. All of these studies have demonstrated that Chinese herbs can promote animal growth by protecting intestinal tract health and regulating intestinal flora structure. However, some studies have shown that a proportion of Chinese herbal additives that is too high can also affect the production performance of sheep. Shi et al. (2024) found that with the increase in the level of Eucommia ulmoides leaf extract additive, ADG and ADFI of Hu sheep initially increased and then decreased.
       
The meta-analysis showed that the addition of Chinese herbal additives to diets could enhance the production performance of sheep to a certain extent, which was aligned with the conclusions reported by Hou et al. (2025). Despite the heterogeneity of the outcome indicators such as ADG, ADFI and F/G, the results also confirmed the reliability of the meta-analysis results after corrective analyses and sensitivity analysis.
 
Effect of Chinese herbal additives on the immune function of sheep
 
Animal immune function reflects health status and determines growth performance and economic outcomes. The levels of immune cytokines and immunoglobulins in the body can reflect the immune status (Liao et al., 2025). Immunoglobulins mainly include IgA, IgG and IgM, which play crucial roles in host defense against external factors (Hernández-Castellano et al., 2015). Li et al. (2025) pointed out that herbal dregs can improve immune function. Qu et al. (2024) showed that Chinese herbal additives could significantly increase IgA, IgG and IgM levels in blood and effectively improve the animals’ immune capacity. Wu et al. (2023) showed that adding 1.5%, 3.0% and 4.5% fermented dregs of Guiqi Yimu Oral Liquid to the basal diet significantly increased the concentrations of IgA, IgG and IgM in Hu sheep serum, possibly because the fermented dregs contain polysaccharides and flavonoid substances. The polysaccharides can enhance anti-tumor immune responses by activating immune cells (Wang et al., 2024) and flavonoids can effectively reduce pro-inflammatory cytokines (Tang et al., 2021). However, some studies showed no significant effects of herbal feed additives on immune function. For example, Zhao et al. (2020) added different proportions of Chinese herbal additives to diets of Tan sheep and found no significant differences in IgA, IgG and IgM levels between groups.
       
The present meta-analysis found that Chinese herbal additives significantly increased serum IgA and IgM levels, significantly decreased IgG concentration. IgG, the most abundant immunoglobulin in blood, is crucial for infection immunity in animals. In the literature reviewed in this study, Li et al. (2021) found that adding 0.3% Astragalus, 0.3% Isatis root and 0.3% Astragalus-Isatis root mixture to the basal diet significantly reduced IgG levels compared with the control group. This study was also the main contributor to the overall reduction in IgG levels. Wang et al. (2021) mixed Astragalus root powder with basal feed and fed it to lambs. After 56 days, they found that the serum concentrations of IgA (P = 0.004), IgG (P = 0.006) and IgM (P = 0.020) were higher than those on day 14. Liu et al. (2023) added 0.8% and 1.6% Astragalus powder and 0.8% and 1.6% Isatis root powder to the basal diet. The results showed that the serum IgG levels in the high-dose Astragalus group were significantly higher than those in other groups. While both high- and low-dose Isatis root powder groups initially showed increased immunoglobulin levels compared to controls at 14 days, these levels decreased below control values by 28 days. None of these observed differences reached statistical significance. The variation in experimental outcomes appears directly linked to several key factors, including the inclusion rates of herbal additives, differences in animal species and duration of feeding trials. Previous studies have been affected by issues such as inconsistent effect measures, significant heterogeneity and potential bias, which may lead to an overestimation of immunomodulatory effects. Future research should further investigate how Chinese herbal medicine affects ruminant immune function to better understand the underlying immunophysiological mechanisms.

Effect of Chinese herbal additives on the meat quality of sheep
 
Cooking yield, drip loss, shear force and pH are important indicators of meat quality (Jin et al., 2022). Xia (2022) demonstrated that Chinese herbal additives had significant promotional effects on sheep farming. Wang et al. (2019) showed that adding 4% Chinese herbal additives to the basal feed could significantly reduce shear force of Hu sheep meat and the present meta-analysis results supported this conclusion. Zhang et al. (2023) showed that adding 0.1% baicalin in the ration could significantly reduce drip loss and water loss rate in the longissimus dorsi muscle of fattening Hu sheep. The results of Wang et al. (2024) demonstrated that the addition of mulberry leaf flavonoids to the feed could significantly reduce the drip loss and improve the quality of mutton. However, this meta-analysis showed that the Chinese herbal additives had no significant effect on the drip loss of mutton. The reasons for the different results of the studies may be attributed to the different levels of nutrition in the diet, herbal ingredients and breeds of sheep. Meat pH is a critical freshness indicator. Pre-slaughter lambs maintain neutral pH. Post-slaughter, glycolytic enzymes convert muscle glycogen to lactic acid, lowering pH. (Zhao et al., 2021). The pH of post-slaughter sheep meat was significantly higher in the antioxidant herbal feed group (0.3% Astragalus polysaccharides) and the flavor-improving herbal feed group compared to the high-concentrate control group (Wang, 2023). This indicates that Astragalus polysaccharides and flavor-improving herbal feed additives can delay post-slaughter glycogen-to-lactic acid conversion in mutton. That is conducive to the maintenance of higher water retention of the muscle of the lamb and obtains higher tenderness, which is consistent with the results of Zhang et al. (2023). Gao et al. (2020) found that the Chinese herbs had no significant effect on the cooking yield of meat, but could significantly improve the brightness of meat and reduce its shear force.
       
The meta-analysis results showed dietary supple-mentation with Chinese herbal additives could moderately enhance sheep meat quality, which aligns with the conclusions of Zhu et al. (2024). Despite the heterogeneity of outcome indicators such as cooking yield, drip loss, shear force and pH, the corrective analyses and sensitivity analyses also confirmed the reliability of the meta-analyses.
 
Limitations of this study
 
This study has certain limitations. First, although high-quality Chinese literature was systematically included, the risks of incomplete data and selective reporting could not be entirely eliminated, with funnel plots indicating minor publication bias that might affect the accuracy of the meta-analysis results. Second, substantial heterogeneity among studies was observed due to variations in basal diet composition and experimental duration, which complicated the interpretation of findings. Furthermore, the current analysis only incorporated selected production performance and economic trait indicators, potentially leading to an incomplete assessment of Chinese herbal additives’ effects. Finally, the inherent limitations of meta-analysis methodology preclude mechanistic investigations into how these additives function or how their effects may vary across different farming conditions. Future research should incorporate larger sample sizes under standardized protocols to establish a more comprehensive evaluation framework for assessing the practical value of Chinese herbal additives in sheep production systems.

CONCLUSION

Firstly, meta-analysis clearly showed that the addition of Chinese herbal additives to diets had a positive effect on ADG, ADFI and F/G of sheep, which had some significance in production practice. Secondly, meta-analysis results showed that the addition of Chinese herbal additives to diets mainly acted on mucosal immunity and significantly increased the concentration of IgA and IgM in serum. Thirdly, meta-analysis results showed that the addition of Chinese herbal additives to diets positively affected mutton cooking yield, pH and shear force, thus the addition of Chinese herbal additives to diets improved meat quality to some extent.
 
Funding
 
This work was supported by China Agriculture Research System of MOF and MARA (CARS-39-35), Qinghai Provincial Science and Technology Department Applied Basic Research (2025-ZJ-719), Qinghai Youth and Middle-aged Science and Technology Talent Support Project (2023QHSKXRCTJ17) and Key Technology Integration and Model Innovation in Sheep Breeding (2021-NK-A5).
 
Author contributions
 
Zhina Du designed the experiments and drafted the manuscript. Data processing and visualization were performed by Wu Sun, Xiayang Jin and Yuhong Ma. and Shike Ma revised the manuscript.
 
Informed consent
 
Informed consent has been obtained from all individuals included in this study.
 
Data availability statement

The datasets generated during and analyzed during the current study are available from the corresponding author on reasonable request.

CONFLICT OF INTEREST

The authors declare that they have no conflicts of interest.

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    Full Research Article

    Meta-analysis of the Effects of Chinese Herbal Additives on the Production Performance, Immune Function and Meat Quality of Sheep

    Z
    Zhina Du1,2,3
    W
    Wu Sun1,2,3,*
    X
    Xiayang Jin1,2,3
    S
    Shike Ma1,2,3
    Y
    Yuhong Ma1,2,3
    1Academy of Animal Science and Veterinary Medicine, Qinghai University, Xining-810016, China.
    2Key Laboratory of Livestock and Poultry Genetics and Breeding on the Qinghai-Tibet Plateau, Ministry of Agriculture and Rural Affairs, Xining-810016, China.
    3Plateau Livestock Genetic Resources Protection and Innovative Utilization Key Laboratory of Qinghai Province, Xining-810016, China.

    ABSTRACT

    Background: This meta-analysis systematically evaluates the effects of Chinese herbal additives on production performance, immune function and meat quality in sheep to support their application in ruminant nutrition.

    Methods: A total of 13 studies, comprising 37 controlled trials, were included in the analysis. The overall effect size was assessed by forest plots and meta-analysis was conducted to identify sources of heterogeneity, perform sensitivity analysis and evaluate publication bias by funnel plots.

    Result: Dietary supplementation with Chinese herbal additives significantly increased average daily gain (ADG) and average daily feed intake (ADFI) (P<0.05) and reduced the feed-to-gain ratio (F/G) (P<0.05). Immunological analysis showed that serum IgA and IgM levels were elevated (P<0.05). For meat quality parameters, the additives increased cooking yield and pH (P<0.05) and decreased shear force (P<0.05) with no significant effect on drip loss (P>0.05). Funnel plot analysis revealed minimal publication bias and sensitivity analysis confirmed the robustness and reliability of the results. These findings suggested that Chinese herbal additives contributed to enhanced production performance, immune function and meat quality in sheep. Further research should validate these findings through more controlled feeding trials, while exploring the active ingredients and mechanisms of action of Chinese herbal additives.

    INTRODUCTION

    With the development of scale and industrialization of animal husbandry and the arrival of the era of comprehensive anti-antibiotic ban, seeking green, safe and effective feed additives has become the key to the development of the livestock industry. Chinese herbal medicines, with their natural properties, low toxicity, minimal side effects and multi-functionality, demonstrate significant potential in livestock and poultry breeding (Zhang et al., 2024). Numerous studies indicate that Chinese herbal additives have the advantages of promoting growth, enhancing immune function of the body and improving the quality of animal products (Liu et al., 2024; Wei, 2024; Zhang et al., 2024). Chen et al. (2021) reported that a Chinese herbal polysaccharide mixture (CMP), formulated with Lycium barbarum and Astragalus membranaceus at a 2:1 ratio, enhanced ADG and increased the serum concentrations of IgA, IgG and IgM. Additionally, CMP treatment elevated the relative abundance of Fibrobacteria, altered rumen microbial fermentation patterns, improved immune function and ultimately enhanced growth performance. Similarly, Ma et al. (2024) added different concentrations of salvia sclarea extract to the diet of 2-month-old Chinese Merino lambs and also arrived at the same conclusion. In sheep breeding production, Chinese herbal additives have shown many significant advantages, serving as an effective strategy to improve breeding efficiency. Research suggests that incorporating an appropriate amount of Chinese herbal additives into the diet of sheep can effectively improve the production performance of sheep. On the one hand, herbs can regulate the feed flavor, increase the feed intake, promote the digestion and absorption of nutrients, thus significantly increasing the daily weight gain and shortening the fattening cycle. On the other hand, by regulating the rumen development, it improves the feed digestive utilization and reduces the breeding costs (Du, 2023; Huang, 2023; Karnani Monika et al., 2020). Chinese herbal additives also exhibit unique immunomodulatory effects (Li et al., 2020). Many Chinese herbs are rich in polysaccharides, organic acids, alkaloids, volatile oils, anthracenes, etc. These substances can regulate the immune function of the animal body and promote the development of immune organs and enhance cellular immune response (He, 2016; Zhang et al., 2016). Herbs can significantly enhance the meat quality by enhancing meat tenderness, flavor and reducing fat content (Wang, 2016; Xia, 2022). At present, there have been many studies on the addition of Chinese herbal additives to sheep diets by domestic and foreign animal husbandry experts, but the quality of the studies varies and the experimental results have not yet been widely recognized due to the differences in feeding methods, raw material composition and processing methods (Zhang, 2023; Zhou et al., 2024).
                   
    Meta-analysis significantly enhances the credibility and generalizability of research by systematically integrating multiple independent studies, providing more reliable evidence for scientific decision-making. (Zhang et al., 2023). Meta-analysis was conducted on literature related to the production performance, immune function and meat quality of sheep with Chinese herbal additives from 2005 to 2022, screened from Chinese databases. The aim was to provide a statistical evaluation of these effects, offering a scientific basis for the rational application of Chinese herbal additives in sheep production.

    MATERIALS AND METHODS

    Literature search
     
    A literature search was conducted in the China National knowledge infrastructure (CNKI), Wanfang Database, VIP database and Chinese science citation database (CSCD). Keywords included “Chinese herbal additives,” “sheep,” “production performance,” “immune function” and “meat quality.” Production performance indicators included average daily gain (ADG), average daily feed intake (ADFI) and feed-to-gain ratio (F/G); immune indicators included IgA, IgM and IgG levels; meat quality indicators included pH, drip loss, shear force and cooking yield. Studies from 2005 to 2022 were included in the search.
     
    Literature screening
     
    In this study, literature selection was conducted based on the following criteria: 1) Studies must include the effects of Chinese herbal additives on production performance, immune function and meat quality of sheep; 2) The results of the study must include the outcome indicators of production performance, such as ADG, ADFI and F/G, the outcome indicators of immune function, such as serum IgA, IgG and IgM levels and the outcome indicators of meat quality, such as pH, drip loss, shear force and cooking yield; 3) The study must have both a control group and an experimental group; 4) Studies must be published in Chinese. All retrieved literature was independently screened, extracted and reviewed by two researchers. A total of 50 papers were retrieved according to the rules of literature search, among which 37 duplicates, conference papers, conference abstracts and unpublished papers were excluded and 13 papers were finally included.
     
    Data extraction and characteristics
     
    This study selected 13 articles, encompassing 37 controlled trials based on experimental designs. The following data and information were extracted: article title, publication year, sample size, concentration of Chinese herbal additives in experimental diets, the experimental data and the standard deviation. When multiple studies shared the same publication year and author, they were distinguished using superscript numbers (1), (2), (3), (4). A total of 13 papers were included in this meta-analysis, including 16 ADG studies, 16 ADFI studies, 16 F/G studies, 11 IgA studies, 11 IgG studies, 11 IgM studies, 8 pH studies, 5 drip loss studies, 4 shear force studies and 10 cooking yield studies. All included studies were controlled trials involving Chinese herbal additives.
     
    Statistical analysis
     
    Because production performance, immune function and meat quality outcomes were continuous variables, we used the standardized mean difference (SMD) as the effect size metric (Zhang et al., 2023). In this study, the SMD method developed by Hedges et al. (1985) and Cohen (1988) was used to evaluate the effect of herbs on the feeding effects (production performance, immune function, meat quality) of sheep. We determined the 95% confidence interval (CI) for all measured parameters and reported their 95% CI values. Detailed procedures are described in the Appendix. Meta-analyses were performed using the Python throughout and effect sizes were pooled using the Cohen or Hedges method in the metacont command. In addition, this analysis was assessed using the I2 method for between-study heterogeneity. When I2<50%, inter-study heterogeneity was considered to be low or non-existent, the effect sizes were pooled using fixed-effects model; when I2>50%, high inter-study heterogeneity was considered to exist. The effect sizes were pooled using the random-effects model. When the 95% confidence interval of the SMD++ did not overlap zero, it was considered that the feed additive group had a significant effect on the production performance, immune function and meat quality outcome indicators of sheep relative to the control group. When the SMD++ was greater than 0, it was considered that the feed additive group had a positive effect on the variable, while the opposite indicated a negative effect. To ensure the authenticity and accuracy of this analysis, funnel plot was used for bias analysis of published articles. Sensitivity analysis was conducted using Leave-one-out analysis. Sensitivity analysis is usually carried out by excluding each study in turn, assessing the impact of that study on the pooled effect size and heterogeneity, then evaluating the stability of the results.

    RESULTS AND DISCUSSION

    Meta-analysis of Chinese herbal additives on production performance of sheep
     
    The meta-analysis demonstrated that there was inter-study heterogeneity (P<0.01, I²>50%) in the quantitative changes in the outcome indicators of production performance represented by ADG, ADFI and F/G after the addition of Chinese herbal additives to the feed, so the random-effects model was applied to pool the effect sizes. The pooled effect sizes of ADG and ADFI were to the right of the null line and the pooled effect size of F/G was to the left of the null line, with none of them intersecting the null line (Fig 1a). The meta-analysis indicated that the addition of Chinese herbal additives to feed significantly increased ADG and ADFI (P<0.05) and significantly decreased F/G (P<0.05). Based on this meta-analysis, these findings suggest that Chinese herbal additives significantly improved the production performance of sheep.

    Fig 1: Forest plot showing the effect of Chinese herbal additives on (1a) ADG, ADFI and F/G; (1b) serum IgA, IgG and IgM levels; (1c) cooking yield, pH, drip loss and shear force in sheep.


     
    Meta-analysis of Chinese herbal additives on immune function of sheep
     
    The meta-analysis showed that there was inter-study heterogeneity in the quantitative changes in the outcome indicators of immune function represented by serum IgA, IgG and IgM levels after the addition of Chinese herbal additives to the feed (P<0.01, I²>50%) and therefore the pooled effect sizes were analyzed using a random-effects model. The pooled effect sizes for IgA and IgM were to the right of the null line and the pooled effect size for IgG was to the left of the null line, with none of them overlapping the null line (Fig 1b). Thus, the meta-analysis indicated that the addition of Chinese herbal additives to feed significantly increased serum IgA and IgM levels (P<0.05) and significantly decreased IgG levels (P<0.05). Based on this meta-analysis, these results suggest that Chinese herbal additives can significantly enhance the immune function of sheep.

    Meta-analysis of Chinese herbal additives on meat quality of sheep
     
    The meta-analysis showed that there was inter-study heterogeneity (P<0.01, I²>50%) in the quantitative changes of meat quality outcome indicators represented by cooking yield, drip loss, shear force and pH after the addition of Chinese herbal additives to the feed, so the random-effects model was applied to pool the effect sizes. The pooled effect sizes of cooking yield and pH were to the right of the null line and the pooled effect size of shear force was to the left of the null line, with none of them intersecting the null line (Fig 1c). Thus, the meta-analysis indicated that the addition of Chinese herbal additives to feed significantly increased cooking yield and pH (P<0.05) and significantly decreased shear force (P<0.05), indicating improved meat tenderness, but had no significant effect on drip loss (P>0.05). Based on this meta-analysis, these results suggest that Chinese herbal additives could significantly improve the meat quality of sheep.
     
    Sensitivity analyses
     
    Chinese herbal additives significantly influenced sheep production performance, immune function and meat quality. This meta-analysis revealed substantial heterogeneity (P<0.01, I²>50%). These variations may relate to differences in sheep breeds, herbal additive compositions and inclusion rates, basal diets and farm management practices. We conducted sensitivity analyses to evaluate result stability and credibility (Table 1). After sequentially excluding each included study, the pooled effect sizes of the remaining studies were distributed on both sides of the null line without overlapping it, further supporting the accuracy of the findings (Fig 2).

    Table 1: Results of meta-analysis of the effects of Chinese herbal additives on production performance, immunity function and meat quality of sheep.




    Fig 2: Sensitivity analysis showing the effect of Chinese herbal additives on (2a) ADG, ADFI and F/G; (2b) serum IgA, IgG and IgM levels; (2c) cooking yield, pH, drip loss and shear force in sheep.


     
    Bias analysis
     
    The studies on production performance, meat quality and immune function outcome indicators were predominantly concentrated in the middle and upper regions of the funnel plot and demonstrated good symmetry (Fig 3). This distribution pattern indicated that the sample size of this meta-analysis was sufficient and representative, the experimental precision was high and the data were reliable. However, several studies were located in the outer regions of the funnel plot, suggesting the presence of some publication bias in this study.

    Fig 3: Funnel plot showing publication bias in the effect of Chinese herbal additives on (3a) ADG, ADFI and F/G; (3b) serum IgA, IgG and IgM levels; (3c) cooking yield, pH, drip loss and shear force in sheep.


     
    Effect of Chinese herbal additives on the production performance of sheep
     
    Chinese herbal medicine can optimize intestinal development and flora, enhance digestive function and improve production performance (Li et al., 2024; Shao et al., 2025). The meta-analysis results demonstrated that the inclusion of Chinese herbal additives in diets led to significant increases in ADG and ADFI, accompanied by a significant decrease in F/G. These findings are consistent with previous studies by Liang et al. (2013). Chinese herbs, containing rich nutrients such as alkaloids, organic acids, trace elements and digestive enzymes, not only provide essential nutrients for growth and development but also promote feed nutrient decomposition, thereby enhancing production performance (Feng et al., 2024). Bao et al. (2019) found that astragalus polysaccharide could significantly increase Tibetan sheep’s ADG and ADFI and decrease F/G. This effect is probably attributable to its polyphenols’ ability to regulate rumen micro-ecological balance, promote the growth of beneficial bacteria and enhance beneficial bacteria activity, ultimately improving the production performance. All of these studies have demonstrated that Chinese herbs can promote animal growth by protecting intestinal tract health and regulating intestinal flora structure. However, some studies have shown that a proportion of Chinese herbal additives that is too high can also affect the production performance of sheep. Shi et al. (2024) found that with the increase in the level of Eucommia ulmoides leaf extract additive, ADG and ADFI of Hu sheep initially increased and then decreased.
           
    The meta-analysis showed that the addition of Chinese herbal additives to diets could enhance the production performance of sheep to a certain extent, which was aligned with the conclusions reported by Hou et al. (2025). Despite the heterogeneity of the outcome indicators such as ADG, ADFI and F/G, the results also confirmed the reliability of the meta-analysis results after corrective analyses and sensitivity analysis.
     
    Effect of Chinese herbal additives on the immune function of sheep
     
    Animal immune function reflects health status and determines growth performance and economic outcomes. The levels of immune cytokines and immunoglobulins in the body can reflect the immune status (Liao et al., 2025). Immunoglobulins mainly include IgA, IgG and IgM, which play crucial roles in host defense against external factors (Hernández-Castellano et al., 2015). Li et al. (2025) pointed out that herbal dregs can improve immune function. Qu et al. (2024) showed that Chinese herbal additives could significantly increase IgA, IgG and IgM levels in blood and effectively improve the animals’ immune capacity. Wu et al. (2023) showed that adding 1.5%, 3.0% and 4.5% fermented dregs of Guiqi Yimu Oral Liquid to the basal diet significantly increased the concentrations of IgA, IgG and IgM in Hu sheep serum, possibly because the fermented dregs contain polysaccharides and flavonoid substances. The polysaccharides can enhance anti-tumor immune responses by activating immune cells (Wang et al., 2024) and flavonoids can effectively reduce pro-inflammatory cytokines (Tang et al., 2021). However, some studies showed no significant effects of herbal feed additives on immune function. For example, Zhao et al. (2020) added different proportions of Chinese herbal additives to diets of Tan sheep and found no significant differences in IgA, IgG and IgM levels between groups.
           
    The present meta-analysis found that Chinese herbal additives significantly increased serum IgA and IgM levels, significantly decreased IgG concentration. IgG, the most abundant immunoglobulin in blood, is crucial for infection immunity in animals. In the literature reviewed in this study, Li et al. (2021) found that adding 0.3% Astragalus, 0.3% Isatis root and 0.3% Astragalus-Isatis root mixture to the basal diet significantly reduced IgG levels compared with the control group. This study was also the main contributor to the overall reduction in IgG levels. Wang et al. (2021) mixed Astragalus root powder with basal feed and fed it to lambs. After 56 days, they found that the serum concentrations of IgA (P = 0.004), IgG (P = 0.006) and IgM (P = 0.020) were higher than those on day 14. Liu et al. (2023) added 0.8% and 1.6% Astragalus powder and 0.8% and 1.6% Isatis root powder to the basal diet. The results showed that the serum IgG levels in the high-dose Astragalus group were significantly higher than those in other groups. While both high- and low-dose Isatis root powder groups initially showed increased immunoglobulin levels compared to controls at 14 days, these levels decreased below control values by 28 days. None of these observed differences reached statistical significance. The variation in experimental outcomes appears directly linked to several key factors, including the inclusion rates of herbal additives, differences in animal species and duration of feeding trials. Previous studies have been affected by issues such as inconsistent effect measures, significant heterogeneity and potential bias, which may lead to an overestimation of immunomodulatory effects. Future research should further investigate how Chinese herbal medicine affects ruminant immune function to better understand the underlying immunophysiological mechanisms.

    Effect of Chinese herbal additives on the meat quality of sheep
     
    Cooking yield, drip loss, shear force and pH are important indicators of meat quality (Jin et al., 2022). Xia (2022) demonstrated that Chinese herbal additives had significant promotional effects on sheep farming. Wang et al. (2019) showed that adding 4% Chinese herbal additives to the basal feed could significantly reduce shear force of Hu sheep meat and the present meta-analysis results supported this conclusion. Zhang et al. (2023) showed that adding 0.1% baicalin in the ration could significantly reduce drip loss and water loss rate in the longissimus dorsi muscle of fattening Hu sheep. The results of Wang et al. (2024) demonstrated that the addition of mulberry leaf flavonoids to the feed could significantly reduce the drip loss and improve the quality of mutton. However, this meta-analysis showed that the Chinese herbal additives had no significant effect on the drip loss of mutton. The reasons for the different results of the studies may be attributed to the different levels of nutrition in the diet, herbal ingredients and breeds of sheep. Meat pH is a critical freshness indicator. Pre-slaughter lambs maintain neutral pH. Post-slaughter, glycolytic enzymes convert muscle glycogen to lactic acid, lowering pH. (Zhao et al., 2021). The pH of post-slaughter sheep meat was significantly higher in the antioxidant herbal feed group (0.3% Astragalus polysaccharides) and the flavor-improving herbal feed group compared to the high-concentrate control group (Wang, 2023). This indicates that Astragalus polysaccharides and flavor-improving herbal feed additives can delay post-slaughter glycogen-to-lactic acid conversion in mutton. That is conducive to the maintenance of higher water retention of the muscle of the lamb and obtains higher tenderness, which is consistent with the results of Zhang et al. (2023). Gao et al. (2020) found that the Chinese herbs had no significant effect on the cooking yield of meat, but could significantly improve the brightness of meat and reduce its shear force.
           
    The meta-analysis results showed dietary supple-mentation with Chinese herbal additives could moderately enhance sheep meat quality, which aligns with the conclusions of Zhu et al. (2024). Despite the heterogeneity of outcome indicators such as cooking yield, drip loss, shear force and pH, the corrective analyses and sensitivity analyses also confirmed the reliability of the meta-analyses.
     
    Limitations of this study
     
    This study has certain limitations. First, although high-quality Chinese literature was systematically included, the risks of incomplete data and selective reporting could not be entirely eliminated, with funnel plots indicating minor publication bias that might affect the accuracy of the meta-analysis results. Second, substantial heterogeneity among studies was observed due to variations in basal diet composition and experimental duration, which complicated the interpretation of findings. Furthermore, the current analysis only incorporated selected production performance and economic trait indicators, potentially leading to an incomplete assessment of Chinese herbal additives’ effects. Finally, the inherent limitations of meta-analysis methodology preclude mechanistic investigations into how these additives function or how their effects may vary across different farming conditions. Future research should incorporate larger sample sizes under standardized protocols to establish a more comprehensive evaluation framework for assessing the practical value of Chinese herbal additives in sheep production systems.

    CONCLUSION

    Firstly, meta-analysis clearly showed that the addition of Chinese herbal additives to diets had a positive effect on ADG, ADFI and F/G of sheep, which had some significance in production practice. Secondly, meta-analysis results showed that the addition of Chinese herbal additives to diets mainly acted on mucosal immunity and significantly increased the concentration of IgA and IgM in serum. Thirdly, meta-analysis results showed that the addition of Chinese herbal additives to diets positively affected mutton cooking yield, pH and shear force, thus the addition of Chinese herbal additives to diets improved meat quality to some extent.
     
    Funding
     
    This work was supported by China Agriculture Research System of MOF and MARA (CARS-39-35), Qinghai Provincial Science and Technology Department Applied Basic Research (2025-ZJ-719), Qinghai Youth and Middle-aged Science and Technology Talent Support Project (2023QHSKXRCTJ17) and Key Technology Integration and Model Innovation in Sheep Breeding (2021-NK-A5).
     
    Author contributions
     
    Zhina Du designed the experiments and drafted the manuscript. Data processing and visualization were performed by Wu Sun, Xiayang Jin and Yuhong Ma. and Shike Ma revised the manuscript.
     
    Informed consent
     
    Informed consent has been obtained from all individuals included in this study.
     
    Data availability statement

    The datasets generated during and analyzed during the current study are available from the corresponding author on reasonable request.

    CONFLICT OF INTEREST

    The authors declare that they have no conflicts of interest.

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