Squabs typically refer to pigeons aged between 29 and 60 days that have left their parents and are transitioning to independent breeding (Liang et al., 2025). This period represents a critical stage of growth and development, during which their digestive system is still immature, with insufficient digestive enzyme secretion and underdeveloped intestinal villi, limiting their ability to effectively digest and absorb feed (Shan et al., 2019). Additionally, squabs undergo a significant transition from reliance on parental milk to self-feeding. Pigeons’ milk is rich in immune factors, and during early life, their immunity is primarily supported by maternal antibodies (Li et al., 2012). However, when squabs become young pigeons, they lose this maternal antibody protection, and their immature immune systems make them vulnerable. Moreover, a series of environmental stresses, such as leaving their parents, beginning self-feeding, and changes in housing and feed, negatively affect their health (Yang et al., 2010). Therefore, identifying a green, safe, and effective feed additive has become a viable solution to address these challenges. Ellagic acid (EA), as a novel, safe, and eco-friendly additive, offers potential benefits in enhancing animal growth performance, promoting nutrient absorption, and modulating gut microbiota (Wang, 2023). Xiao showed that EA protects against oxidative damage induced by paraquat in piglets, enhances intestinal barrier integrity, and alleviates systemic oxidative stress through the Nrf2 pathway (Xiao et al., 2022). Wang’s research found that by adding appropriate amount of ellagic acid to the feed, the oxidative stress of broilers can be alleviated, and the contents of serum total protein and albumin can be significantly increased (Wang et al., 2025). Chen found that oral administration of EA increases plasma total protein levels and reduces plasma total bilirubin levels (Chen et al., 2024). Liu found that by adding ellagic acid to the feed, it was found that ellagic acid could adjust the intestinal flora structure of ewes, significantly increase the abundance of beneficial bacteria such as Bifidobacterium and lactic acid bacteria, and reduce the proportion of harmful bacteria such as Escherichia coli and Salmonella. The Shannon and Simpson indices of flora increased significantly, and the intestinal microecological environment became more stable (Liu, 2025).

Although EA has a good protective effect on other livestock and poultry species (such as piglets, broilers and ewes), there is still a key research gap: there is no research focusing on the application of EA in young pigeons during the critical parental separation and nutritional transition period. The existing research on EA has not solved the unique physiological challenges of young pigeons at this stage (such as immature digestion, maternal immunity decline and combined environmental pressure), nor has it explored whether EA can alleviate these challenges to improve the health and production performance of young pigeons. This lack of targeted research hinders the rational application of EA in pigeon breeding industry, especially in the critical period of pigeon’s transition to independence. Based on the above research gaps, this study assumes that: Adding EA to the diet will improve the growth performance and apparent digestibility of nutrients of young pigeons during the transition period of 29–60 days by enhancing digestive function; Supplementing EA will reduce oxidative stress and improve the slaughter performance of young pigeons by regulating serum biochemical indices related to nutritional metabolism and immunity; EA can adjust the composition of fecal microflora of young pigeons, increase the abundance of beneficial bacteria and reduce harmful bacteria, thus stabilizing the intestinal microecological environment. In order to test these hypotheses, this study discussed the effects of different dietary e a levels on the growth performance, apparent nutritional metabolism, slaughter characteristics and fecal microbial diversity of young pigeons, aiming at providing scientific basis for the rational application of EA in pigeon feeding and determining its optimal addition level, so as to enhance the health of young pigeons in the critical transition period.

Animal growth performance is closely linked to food intake, which directly influences nutritional metabolism, growth, and development. Currently, research on the use of EA as an effective substitute for antibiotics in pigeon diets is limited, both domestically and internationally. Due to the incomplete development of the immune system and digestive organs in pigeons, immune function may decline, reducing the efficiency of nutrient digestion and metabolism, ultimately affecting growth performance. Previous research (Baradan Rahimi et al., 2020) has shown that incorporating EA into animal diets can enhance immune function, regulate intestinal flora richness, improve growth performance, and promote overall health. The results of this Test group demonstrated that supplementing the diet with 200 mg/kg EA increased the average daily weight gain and average daily feed intake of young pigeons, while reducing the feed-to-weight ratio. These findings align with previous studies. For instance, adding a suitable amount of EA to broiler diets has been shown to enhance immune function, increase feed intake and daily weight gain, and thereby accelerate healthy growth (Kishawy et al., 2016). Lu observed that adding 500 mg/kg EA to weaned piglet diets significantly improved daily weight gain and reduced diarrhea rates. Additionally (Lu et al., 2022), Gul reported that EA can regulate intestinal flora, improve intestinal health, and support animal growth and development, ultimately benefiting human health (Gul et al., 2022). Wang found that EA supplementation in broiler diets improved the structure and function of the digestive system, enhancing nutrient digestion and absorption, thereby improving growth performance (Wang et al., 2022). In this study, different doses of EA had no statistically significant effect on the apparent metabolic rate of meat pigeons, which may be due to the differences in feeding cycle, individual animals and detection conditions, and EA did not cause significant changes in nutritional digestion and metabolism indexes. This shows that EA can improve the digestion and absorption efficiency of nutrients and promote animal feed intake and weight gain by enhancing immune function, regulating intestinal flora structure and improving the structure and function of digestive system.

Body size is a key index for evaluating the growth and performance of poultry, encompassing parameters such as body height, body oblique length, chest width, chest depth, tibia length, and tibia circumference. These indices not only reflect the development of bones and muscles but are also closely associated with economic traits, such as slaughter performance and meat yield. From the perspective of intestinal health, EA may enhance the intestinal microecological balance, promote nutrient digestion and absorption, and indirectly influence body size traits in poultry.

However, from the body size and weight, we also found a problem, that is, there are advantages between 400mg/kg EA and 200 mg/kg EA. The reasons are as follows: on the one hand, the biggest response of bone development to EA dose is higher: 400 mg/kg EA may provide sufficient physiological motivation for bone growth by promoting osteoblast activity and enhancing mineral element absorption, so the improvement of body shape index is more obvious; On the other hand, 200 mg/kg EA is more conducive to the accumulation of weight gain: this dose can effectively improve the utilization rate of nutrients without causing metabolic pressure on the body, and nutrients may be more like tissue synthesis, showing the peak of daily average weight gain; However, the nutrient distribution of 400 mg/kg EA group may be more inclined to bone mineralization, so the weight gain is slightly lower than that of 200 mg/kg EA group.

A healthy intestinal microbiota is crucial for improving intestinal barrier function, increasing feed conversion efficiency, and providing sufficient nutritional support for poultry growth and development. Moreover, EA may also affect body size development by modulating hormone secretion in poultry. Growth hormone (GH), insulin-like growth factor-1 (IGF-1), and other hormones play a central role in regulating growth and development by promoting chondrocyte proliferation and hypertrophy in the bone growth plate and stimulating muscle growth. In this study, dietary supplementation with varying concentrations of EA revealed that 400 mg/kg EA significantly improved the body size development of 60-day-old pigeons, specifically enhancing chest width, chest depth, and tibia length compared to the other concentration groups. It shows that ellagic acid may promote food intake by regulating the diversity of intestinal flora, and then affect the chest width, chest depth and other indicators.

Slaughter performance is a key indicator for assessing the production performance of meat pigeons, directly influencing economic returns. Generally, higher slaughter performance correlates with greater economic benefits (Li et al., 2024). The slaughter index of poultry is useful for breeding and identifying poultry varieties and serves as an important reference for evaluating the management and nutritional status of poultry. Organ weight reflects the state of organ growth and development and provides insight into metabolism, digestion, absorption, and immune function (Martínez et al., 2021). The results of this Test group showed that the semi-clean bore weight, chest muscle weight, leg muscle weight, and muscle stomach weight of the Test group were significantly higher than those of the control group, indicating that dietary supplementation with EA positively impacted both slaughter performance and organ index. Wang examined the effects of EA on the growth and development of pig breast and leg muscles and meat quality (Wang et al., 2024). Their findings indicated that EA increased breast and leg muscle weight, improved muscle tenderness, and enhanced water retention. Similarly, the results of this study show that the semi-clean bore weight, chest muscle weight and leg muscle weight of young pigeons are significantly increased after EA is added to the diet-this phenotypic change further proves that EA can alleviate the low nutritional and metabolic efficiency of young pigeons due to incomplete immune development by enhancing immune function (such as the increase of IgA and IgG levels in this experiment), thus providing more adequate nutritional and metabolic support for the growth of muscles and other tissues, and finally indirectly promoting the growth and development of the body.

The spleen and bursa of Fabricius are critical immune organs in poultry, and their development reflects the growth and immune function of the birds (Song et al., 2023). Studies have shown that EA promotes the development of immune organs, such as the thymus, spleen, and bursa of Fabricius, through its antioxidant and anti-inflammatory properties (Yang et al., 2022). In broilers, EA supplementation significantly increased thymus and spleen weight, indicating enhanced immune function. These findings highlight the potential of EA in promoting the development and function of immune organs (Wang et al., 2025), consistent with the results of this experiment. The data suggest that EA enhances animal immune function by promoting the development of immune organs, particularly the thymus and bursa of Fabricius. The possible reason is that EA can promote the development of immune organs such as thymus, spleen and bursa of fabricius by virtue of its antioxidant and anti-inflammatory properties, and then promote the immune function of animals themselves.

Immunoglobulins are key indicators of animal immunity. IgA, IgM, and IgG are closely associated with blood diseases, infections, and autoimmune disorders (Fuentes et al., 2019). Among these, IgG represents the largest proportion and plays a pivotal role in maintaining the body’s immune barrier and early defense mechanisms (Vidarsson et al., 2014). IgA exhibits antiviral and bacteriostatic properties, serving as the main effector molecule in humoral and mucosal immunity, directly participating in immune responses. IgM is a high-performance antibody involved in human defense, with bactericidal and antiviral functions (Zhang et al., 2024). The antioxidant properties of EA may reduce oxidative stress-induced damage to immune cells, thereby indirectly enhancing immunoglobulin synthesis and secretion. Deng demonstrated that EA regulates the levels of inflammatory factors, immunoglobulins, and T cells in burned rats, promoting wound healing and improving symptoms of immunosuppression (Deng et al., 2023). In this study, EA supplementation increased the secretion of IgA, IgG, and IgM. These results indicate that EA supplementation improves the humoral immune response and immune system function in pigeons. Although certain doses of EA increased antioxidant enzyme activity and immune markers (such as IgA), the highest dose (400 mg/kg) also elevated MDA levels, suggesting a higher level of potential oxidative stress. At this dose, EA may induce mild oxidative stress (evidenced by a slight increase in reactive oxygen species, or ROS). In response, the body activates a compensatory mechanism, upregulating antioxidant enzymes such as SOD and GSH-Px to eliminate ROS. However, when ROS production exceeds the scavenging capacity of these enzymes, lipid peroxidation is triggered, leading to the accumulation of MDA. Therefore, the increase in MDA may reflect an intermediate state between the initiation of oxidative stress and the incomplete compensation by antioxidant mechanisms, rather than indicating a final “redox imbalance” outcome. In addition, EA can promote the expression and activity of downstream antioxidant enzymes such as SOD and GSH-Px by activating Nrf2 pathway in young pigeons. Activated Nrf2 can regulate the transcription of phase II detoxification enzyme gene and enhance the ability of liver to remove toxic intermediates produced during metabolism. However, it is worth noting that the appropriate dosage of EA of 200 mg/kg can accurately match the antioxidant needs of young pigeons during the transition period, while the dosage of EA of 400 mg/kg is close to the effect threshold, which may be related to the fact that excessive EA exceeds the metabolic capacity of young pigeons and interferes with the steady-state regulation of Nrf2 pathway. It shows that EA can enhance the antioxidant capacity of the body and reduce oxidative stress through multiple ways: on the one hand, it can directly scavenge free radicals and inhibit lipid peroxidation; on the other hand, it can regulate the activity and gene expression of antioxidant enzymes such as SOD, GSH-Px and CAT in blood, and at the same time reduce the level of MDA, thus maintaining cell stability and reducing DNA damage.

Although direct studies on the effect of EA on serum nitrogen metabolism are limited, insights can be drawn from other animal models. For example, in various mouse models, EA has been shown to reduce serum total cholesterol (TC) and triglycerides (TG), while increasing high-density lipoprotein cholesterol (HDL-C) (Xu et al., 2021). This mechanism may involve EA’s regulation of lipid metabolism genes, such as inhibiting the expression of SREBP-1c mRNA and FAS mRNA, and promoting the expression of LPL mRNA to lower lipid levels. While this study primarily focuses on lipid metabolism, the underlying mechanism may be similar to nitrogen metabolism, as both involve the regulation of metabolic pathways. EA supplementation in animal diets may also indirectly influence nitrogen metabolism through its antioxidant and anti-inflammatory effects. Studies have demonstrated that EA has significant antioxidant capacity, reducing oxidative stress and inflammation (BenSaad et al., 2017). This shows that EA can maintain the homeostasis of intracellular environment through these effects, and then ensure the activity and function of enzymes involved in nitrogen metabolism.

EA supplementation has been found to reduce liver function enzyme levels, such as ALT and AST. For instance, in sheep, EA significantly reduced serum ALT and AST levels, thereby improving liver function (Li et al., 2022). Additionally, EA has been shown to mitigate abnormal liver function induced by silver nanoparticles, including lowering ALT and AST levels (Dabbaghi et al., 2023). EA also exhibits immunomodulatory effects, enhancing immune function by increasing serum IL-2 levels (Umesalma and Sudhandiran, 2010 Furthermore, EA possesses anti-inflammatory properties, reducing levels of inflammatory factors. In an experimental rat model, intraperitoneal injection of EA combined with carrageenan-induced paw inflammation demonstrated its long-lasting anti-inflammatory effects, potentially interacting with known cyclooxygenase inhibitors. Additionally, EA may act as a cyclooxygenase inhibitor, exerting anti-inflammatory effects by suppressing the release and activity of inflammatory mediators (Corbett et al., 2010). This shows that EA has triple effects of liver protection, immune enhancement and anti-inflammation, and may play an anti-inflammatory role by enhancing its own immunity and reducing the release of inflammatory mediators, thus alleviating inflammatory stress injury. Thereby improving liver function.

Cortisol, a stress hormone, is closely linked to oxidative stress (Balasundram et al., 2006). Tannin compounds, including EA, are widely present in plants and have demonstrated beneficial effects on the digestive and immune systems (Park et al., 2021). Feeding high-quality feed in combination with low-quality roughage has been shown to elevate serum cortisol concentrations in dairy cows. However, EA supplementation may reduce stress responses through its antioxidant properties, thereby lowering cortisol levels (Bai et al., 2022). Additionally, EA has been found to regulate the expression of leptin, a key protein secreted by adipose tissue, which plays a pivotal role in energy balance and weight regulation (Cisneros-Zevallos et al., 2020). By influencing leptin secretion or receptor expression, EA may positively affect body weight and metabolism. However, the effect of EA on the hormone level of meat pigeons and its related mechanism with production performance still need further verification and clarification in follow-up studies.

Non-starch polysaccharides in plants are not hydrolyzed by enzymes secreted by the host but are instead decomposed and utilized by microorganisms such as Bacteroides and Cladosporium in the intestine, serving as a primary carbon source for intestinal microbiota (Mo et al., 2023). Bacteroides and Cladosporium comprise more than 90% of the total intestinal microbiota, and their wide-ranging functions are attributed to their secretion of various degrading enzymes. EA exerts an antibacterial effect by interacting with bacterial cell wall components, such as NDK protein and GND protein, disrupting the structure (Fan et al., 2022). This may inhibit the formation of biofilms by beneficial bacteria like lactic acid bacteria (Ratti et al., 2023) and indirectly influence bacterial metabolism by regulating apoptosis-related genes (such as Bax and Bcl-2) and antioxidant capacity (Wu, 2018).

The bacteriostatic effect of EA is dose-dependent. At concentrations of 0 mg/kg, 100 mg/kg, 200 mg/kg, and 400 mg/kg, a low concentration (100 mg/kg) may promote the abundance of Firmicutes and Bacteroides through antioxidant effects (Xia et al., 2023). A medium concentration (200 mg/kg) may inhibit certain microbiota, while a high concentration (400 mg/kg) can cause fluctuating abundance levels due to toxicity. This fluctuation may result from the competitive effects of EA, the formation of metabolites, and the regulation of intestinal barrier function (Liu et al., 2016; Wang et al., 2022). Bacilli, as the dominant flora, is capable of protein decomposition (Partanen et al., 2010), while α-Proteobacteria positively correlates with humoral immune IgG levels (Yu, 2023) and impacts feed conversion efficiency along with Clostridia in the jejunum (He, 2021). Notable members include Burkholderia, which secretes antibacterial and anticancer secondary metabolites for bioremediation (Depoorter et al., 2016; Kunakom and Eustáquio, 2019) and serves as a host for heterologous expression (Liu et al., 2021). Lactobacillus bulgaricus, used as a feed additive, synthesizes antioxidant exopolysaccharides (Xu et al., 2017; Sasikumar et al., 2017), regulates immunity (Moro-Garcia et al., 2013), and promotes digestion to improve animal health. Its preparation enhances growth performance and antioxidant capacity in nursing pigs (Niu, 2022). Additionally, Flavobacteriia IIA improves nutrient utilization through pantothenic acid synthesis (Clemmons et al., 2019), and changes in the abundance of Fusobacteriia and Gammaproteobacteria are associated with diarrhea, stress (Liu, 2021), and potential pathogenicity, respectively. Sphingomonas tolerates environmental stress through its antioxidant properties, and Acidovorax creates an acidic microenvironment through acid production (Huang et al., 2024), influencing microbiota balance.

Although this study initially revealed the improvement of growth performance, immune function and antioxidant capacity of meat pigeons by adding EA to the diet, and explained some regulatory mechanisms, there were still some limitations. In this study, the effect of EA was analyzed only by serum biochemical indicators and routine immune indicators, and the combined analysis of metabonomics, transcriptomics and other multi-omics technologies was not carried out, so it was difficult to intuitively and accurately analyze the molecular network and key targets of EA regulating intestinal metabolism-immunity-growth axis of meat pigeons. Future research can integrate multi-omics technology, combined with intestinal histological observation and functional gene verification, further clarify the core pathway of EA to improve the meat quality of meat pigeons, and provide more comprehensive theoretical support for its application as an antibiotic substitute in poultry breeding.

In conclusion, supplementing the diet with EA can enhance growth performance, immunity, total protein content, and help maintain the richness and stability of the intestinal microbiota in young pigeons. The optimal effect is observed with the addition of 200 mg/kg EA to the feed.