Many countries paid much attention to develop strategies for rabbit production sustainability, as rabbit meat is one of the most important sources of animal protein around the world (Šufliarsky et al., 2024). Weaned rabbits are very susceptible to intestinal troubles as a consequence of banning antibiotics as growth enhancers because of their special and distinguished digestive system (Volek et al., 2018; Ebeid et al., 2022). In rabbits, the weaning and post-weaning stages are most vital to support growth and stability against digestive troubles (Fortun-Lamothe and Boullier, 2007). Moreover, there is a growing interest in the requirement for antibiotic-free and organic rabbit products. Probiotics are live microorganisms added to animal and poultry diets to modulate gut microbiota in order to enhance health and performance (Pogány Simonová et al., 2020; Wang et al., 2020; Abd El-Moneim et al., 2020). The probiotic microorganisms usually added to rabbit diets include bacteria (e.g., Lactobacillus, Lactococcus, Bacillus, Bifidobacterium, Enterococcus faecium), fungi (e.g., Aspergillus awamori), and yeasts (e.g., Saccharomyces cerevisiae). Probiotics supplementation had a positive effect on growth performance and gut health (Wang et al., 2020; Wlazło et al., 2021). Also, probiotics improved antioxidative properties (El-Deep et al., 2021) and immune responsiveness (Guo et al., 2017). These enhancements could be related to: (1) competitive expulsion for the pathogenic microorganisms (Helal et al., 2021), (2) greater absorption of essential nutrients (Elbaz et al., 2023), (3) improving the digestion and absorption (Abdel-Wareth et al., 2021), and (4) manufacturing of antimicrobial molecules (Pogány Simonová et al., 2020). In the recent years, probiotics get much attention. Thus, the present review is an endeavour to explain the recent results linked to the benefits of supplemental probiotics on gut microbiome, gut architecture, nutrients’ digestion and absorption, antioxidative properties, immune responsiveness, and productivity in rabbits.
Put microbiome is a vital component in the intestinal mucosal barrier which increases the gut health and host defence (Fortun-Lamothe and Boullier, 2007). Several studies documented that probiotic addition modified microorganisms’ populations because probiotic strains are able to settle the gastrointestinal tract (GIT) of rabbits (Phuoc and Jamikorn, 2017; Shen et al., 2020; Wlazło et al., 2021; Helal et al., 2021). Supplemental probiotics are responsible for prohibiting the development and propagation of pathogenic bacteria, and stimulating the helpful bacteria that have a central role in digestion, vitamin manufacturing, volatile fatty acids (VFA) construction, and antimicrobial peptides synthesis (Mancini and Paci, 2021). Phuoc and Jamikorn (2017) illustrated that supplementation of Lactobacillus acidophilus (1×106 CFU/g diet) or mixture of (0.5×106 CFU/g Bacillus subtilis + 0.5×107 CFU/g L. acidophilus) increased GIT useful bacteria count (Lactobacilli and Bacilli), and decreased coliforms’ count in growing rabbits. Recently, Elbaz et al. (2023) observed that dietary Saccharomyces cerevisiae (5 g/kg diet) increased Lactobacillus count and minimized E. coli count in cecum of New Zealand White (NZW) growing rabbits. An increase in Lactobacilli count and decrease in number of coliforms and number of anaerobic bacteria, due to probiotics administration, were also documented by Oso et al. (2013), Shen et al. (2020) and Abdel-Azeem et al. (2018). Wlazło et al. (2021) noted that addition of a fermented rapeseed meal plus Bacillus subtilis increased number of lactic acid bacteria and reduced counts of coliforms and E. coli in the small intestine and colon of growing NZW × Popielno White rabbits. These findings agree with those of Helal et al. (2021) which showed that addition of 0.1% combination of Saccharomyces cerevisiae (1×108 CFU/g) and Bacillus subtilis (3×107 CFU/g) minimized the pathogens count (E. coli and Clostridium perfringens) and increased the count of Lactobacillus in growing rabbits. Also, Pogány Simonová et al. (2020) showed that addition of Enterococcus faecium CCM7420 increased faecal enterococci and lactic acid bacteria counts as well as decreased of faecal coliforms, Pseudomonas-like spp., Clostridium-like spp. and Staphylococcus aureus in broiler rabbits. Wang et al. (2020) pointed out that dietary supplementation of a mixture of three Bacillus strains (1.0 × 105 – 1.0 × 107 CFU/g) increased the concentrations of Lactobacillus spp. and Bacillus spp., and elevated the abundance of Ruminococcus flavefaciens and Fibrobacter succinogenes as well as reduced E. coli concentration in cecal contents in growing Rex rabbits. In another study, Liu et al. (2019) confirmed that dietary supplementation of Clostridium butyricum (1.0 × 104 – 1.0 × 105 CFU/g) elevated the abundance of total bacteria, Ruminococcus albus, Ruminococcus flavefaciens, Firmicutes, Butyrivibrio fibrisolvens, Bacteroidetes, Clostridium cluster IV, Clostridium cluster XIVa, Lactobacillus, and Bifidobacterium in duodenum, jejunum, ileum, cecum, and colon in growing rabbits. In another study by Guo et al. (2017), growing rabbits supplemented with Bacillus subtilis (1.0 × 106 CFU/g) showed higher relative abundance of Ruminococcus and reduced percentage of Bacteroides and Clostridium at the phylum level. The Ruminococcus participate in fibre digestion and absorption in rabbits. Therefore, the reduction of pathogenic bacteria might be attributed to increased intestinal VFAs concentration leading to reduced pH which suppress the development and propagation of pathogenic bacteria (Phuoc and Jamikorn, 2017; Pogány Simonová et al., 2020; Wang et al., 2020). Recently, Xia et al. (2024) observed that dietary heat-killed Lactobacillus acidophilus (800 mg/kg) increased the relative abundance of Phascolarctobacterium and Alistipes in the cecum of growing rabbits. Additional explanations have been put forth to account for the barrier effect: (i) The adhesion of beneficial bacteria to the mucosa can stop harmful germs from attaching and colonizing, (ii) The beneficial bacteria absorb all available resources and prevent the pathogens from getting their requirements, (iii) By generating antimicrobial compounds, the beneficial bacteria are able to prevent the growth of rival microbes (Combes et al., 2013; Ebeid et al., 2021 a).
Efficient GIT function and health is characterized by efficient structure and function of the GIT barrier, balanced microbiota, useful digestion and absorption, and perfect immune status. Probiotics supplementation has a positive impact on gut health including gut histomorphology, microflora, digestive enzymes, and intestinal mucosal immunity and health.
Greater villus height, minimal crypt depth, greater villus: crypt ratio, and other physiological traits of the intestines are indicative of an increase in absorption surface area. Additionally, because goblet cells make mucin to coat the epithelial surface and stop dangerous pathogens from adhering to it, they are a good sign of the intestinal health (Fortune-Lamothe and Boullier, 2007; Ebeid and Al-Homidan, 2022). Numerous researchers have demonstrated the beneficial effects of probiotic supplementations on intestinal histomorphology, as evidenced by increasing the villus height, reducing crypt depth, and elevating the villi height: crypt depth (VH:CD) ratio in the GIT of rabbits (Pogány Simonová et al., 2015; Liu et al., 2019; El-Deep et al., 2021). Pogány Simonová et al. (2015) elucidated that administration of Enterococcus faecium CCM7420 strain (5.0 × 108 CFU/rabbit/d in drinking water) increased the villus surface area and VH:CD ratio in broiler rabbits. Recently, Elbaz et al. (2023) proved that dietary Saccharomyces cerevisiae (5 g/kg diet) enhanced ileal villus height and VH:CD ratio of NZW broiler rabbits. Similarly, Wang et al. (2020) indicated that dietary supplementation of a mixture of three Bacillus strains (1.0 × 105 – 1.0 × 107 CFU/g) enhanced villus height and VH:CD ratio as well as decreased crypt depth in jejunum in growing Rex rabbits. Also, El-Deep et al. (2021) observed that addition of Aspergillus awamori (100 or 150 mg/kg diet) improved the gut villi traits (height and thickness). In another study, Liu et al. (2019) confirmed that inclusion of Clostridium butyricum (1.0 × 104 – 1.0 × 105 CFU/g) in feed elongated the height of the villi and VH:CD and reduced the depth of crypts in duodenum, jejunum, and ileum of weaning Rex rabbits. These data are consistent with those of Seyidoglu and Peker (2015), who noted that dietary administration of 2–4 g Saccharomyces cerevisiae per kg diet had a beneficial impact on duodenum morphology including increasing the villus height, crypt depth, gland depth, and total mucosa in rabbits. Furthermore, dietary probiotic supplementations have a positive effect on length of GIT and its parts. Nwachukwu et al. (2021) postulated that dietary Lactobacillus acidophilus, Saccharomyces boulardii, and Saccharomyces cerevisiae (50 mg/kg diet) increased the length of GIT and its segments (oesophagus, small and large intestines) and improved the intestinal histomorphology parameters in the form of increased villus height, villus width, and villus density, while crypt depth was lessened in Chinchilla × NZW growing rabbits. Likewise, Helal et al. (2021) showed that dietary addition of 0.1% probiotics (blend of Saccharomyces cerevisiae plus Bacillus subtilis) elevated the length of small intestine by 10% in comparison with the control group in growing NZW rabbits. Moreover, dietary supplementation of Saccharomyces cerevisiae, Bacillus subtilis or their mixture enhanced the length of ileal villi and reduced the ileal muscular layer thickness in comparison with the un-supplemented group. Therefore, it is crucial to note that dietary inclusion of probiotic may contribute to the growth of goblet cells and gut villus-crypt units, which in turn may enhance the digestion and absorption of nutrients.
Probiotics may improve the digestive system’s physiological efficiency through two main mechanisms: the synthesis of digestive enzymes and changing the morphology of the GIT villi. El-Deep et al. (2021) observed that dietary inclusion of Aspergillus awamori (100 or 150 mg/kg diet) enhanced digestibility coefficients of protein, lipids, and fibres in growing rabbits. These results agree with several trials which noted that dietary probiotics improved digestibility coefficients in rabbits (Bhatt et al., 2017; Phuoc and Jamikorn, 2017; Liu et al., 2019). Bhatt et al. (2017) indicated that dietary supplementation of Lactobacillus acidophilus and Lactococcus lactis (1.0 × 107 CFU/g) elevated digestibility of dry matter, organic matter, fibres and crude protein in growing Chinchilla rabbits. Recently, Elbaz et al. (2023) observed that dietary Saccharomyces cerevisiae (5 g/kg diet) improved all nutrients’ digestibility in NZW growing rabbits. Abdel-Wareth et al. (2021) observed that supplying growing rabbits’ diets with 450 mg probiotics/kg diet (Lactobacillus acidophilus, Lactobacillus plantarum, Bifidobacterium bifidum, Bacillus subtilis fermentation extract, and Aspergillus niger fermentation extract) enhanced nutrient digestibility (crude protein, ether extract, energy, and crude fibre) in growing rabbits. These enhancements in digestibility coefficients might be attributed to increasing the secretion of digestive enzymes such as cellulase, xylanase, and protease (Phuoc and Jamikorn, 2017; Guo et al., 2017). Wang et al. (2020) confirmed that dietary supplementation of a mixture of three Bacillus strains (1.0 × 105 – 1.0 × 107 CFU/g) heightened the activities of protease and amylase in duodenum and ileum, protease activity in jejunum, cellulase activity in cecum of growing Rex rabbits. Recently, Xia et al. (2024) observed that dietary heat-killed Lactobacillus acidophilus (800 mg/kg) enhanced trypsin and fibrinase activities and consequently enhanced apparent digestibility of crude protein and crude fibre in growing rabbits. These findings showed that digestion of protein, starch, and cellulose function were improved by probiotics. Furthermore, Aspergillus awamori may enhance the release of amylases, cellulases, xylanases, and proteases as well as it can destroy the antitrypsin and antinutritional factors that are found in soybean meal and consequently enhance the proteins and lipids absorption in the GIT (de Castro et al., 2015). Moreover, numerous studies proved that dietary supplementation of probiotics improved cecal fermentation and increased intestinal VFAs concentration leading to reduce pH and consequently improve nutrient digestibility in rabbits (Phuoc and Jamikorn, 2017; Pogány Simonová et al., 2020). Also, Wang et al. (2020) showed that addition of Bacillus strains elevated the VFAs concentrations (acetic, propionic, and butyric acids) of cecal contents in growing rabbits. Likewise, addition of E. faecium CCM7420 to rabbits resulted in increasing acetic acid concentration in faecal contents in comparison with control animals (Pogány Simonová et al., 2009). From an additional point of view, elevation of VFAs concentration reduced pH in the GIT, which might participate in blocking the development and propagation of pathogenic bacteria in rabbits, leading to promote the digestion and absorption of nutrients and improving GIT immunity (Pogány Simonová et al., 2015).
Currently, numerous researchers have an excessive interest in the positive effects of probiotics on GIT health in various animals. The intestinal immune system of the rabbit depends on the lymphoid tissue located mainly in the sacculus rotundus, which is found in the ileo-cecal junction and the vermiform appendix, presented at the end of the cecum (Fortun-Lamothe and Boullier, 2007). The prime role of the rabbit appendix is immunological function rather than digestive function as it is the greatest relative lymphoid site in rabbits (Combes et al., 2013). Shen et al. (2020) pointed out that oral administration of Lactobacillus casei enhanced the length of vermiform appendix in artificially suckling rabbits. The highest development of the vermiform appendix is connected with the enhancing immune efficiency in rabbits. Similarly, Wang et al. (2020) indicated that dietary supplementation of a mixture of three Bacillus strains (1.0 × 105 – 1.0 × 107 CFU/g) increased the vermiform appendix index of growing Rex rabbits. It is well known that Paneth cell is involved in innate immune response via secretion of antimicrobial constituents to the GIT lumen, like lysozyme, defensin, peptides, and secretory phospholipase A2 (Clevers and Bevins, 2013). Moreover, Shen et al. (2020) illustrated that oral administration of Lactobacillus casei enhanced the percentage of degranulated Paneth cells and expression levels of toll-like receptor 9 (TLR9), defensin-7-like (DEFEN), and lysozyme (LYZ) in the duodenum and jejunum in artificially suckling rabbits. Toll-like receptors (TLR) are the first barrier against pathogens and can play a central role in stimulating the secretions of anti-inflammatory cytokines (Chytilová, 2013). These results agree with Liu et al. (2019) who confirmed that dietary inclusion of Clostridium butyricum (1.0 × 104 – 1.0 × 105 CFU/g) increased the relative expressions of MyD88, TLR2, and TLR4 and decreased the pro-inflammatory cytokines (IL-6, INF-γ, and TNF-α) in weaning Rex rabbits. Also, Guo et al. (2017) noted that rabbits supplemented with Bacillus subtilis (1.0 × 106 CFU/g) enhanced the expressions of innate immune-related genes (nucleotide oligomerization domain 1 “NOD1”, NOD-like receptor C3 (“NLRC3”) and NLRX1) in jejunum of growing rabbits. Furthermore, gut epithelium and secretory IgA (sIgA) serve as a natural defence barrier against pathogens and enteric toxins found in the gut lumen. Furthermore, Liu et al. (2019) confirmed that dietary administration of Clostridium butyricum (1.0 × 104 – 1.0 × 105 CFU/g) increased the secretory IgA (sIgA) in the duodenum and ileum of weaning Rex rabbits. Thus, it might be concluded that administration of probiotics is involved in enhancing gut immunity and health via enhancing the GIT lymphoid tissues, gut epithelium, and sIgA, as well as reducing the pro-inflammatory cytokines in the intestine.
Current rabbits are extra vulnerable to oxidative stress because of their elevated metabolic rate, higher fat content, and exposure to numerous unfavourable environments (Abdelsalam et al., 2019). Thus, it is essential to keep the antioxidative system in balance between the production and removal of free radicals under both normal physiological circumstances and under stress circumstances (Ebeid et al., 2023). Probiotics can stimulate the antioxidative enzymes responsible for eliminating the reactive oxygen species (ROS, including glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and catalase (CAT)) and minimizing lipid peroxidation in the form of reducing concentration of malondialdehyde (MDA) in rabbits (Liu et al., 2019; Wang et al., 2020; El-Deep et al., 2021; Elbaz et al., 2023). Arram et al. (2018) proved that administration of Lactobacillus acidophilus decreased MDA, reduced glutathione, oxidized glutathione, and nitric oxide in liver of growing rabbits. Also, Wang et al. (2020) indicated that dietary supplementation of a mixture of three Bacillus strains improved activities of SOD, GSH-Px, and CAT as well as reduced MDA concentrations in serum of growing Rex rabbits. Also, El-Deep et al. (2021) observed that addition of Aspergillus awamori improved the CAT activity and decreased MDA concentration in growing rabbits. These results confirmed the previous study (Abdelhady et al., 2017) which indicated that Aspergillus awamori enhanced the antioxidative properties in rabbits via upregulating the antioxidative-sensitive genes including heme oxygenase-1 (HO-1) and superoxide dismutase type 1 (SOD1). In fact, the GIT epithelium is more susceptible to oxidative damage caused by ROS and consequently deteriorating GIT health (Abdel-Moneim et al., 2021). Thus, enhancing antioxidant capacity of gut tissues is important for rabbits’ growth and health (Ebeid et al., 2013). Interestingly, Xia et al. (2024) observed that dietary heat-killed Lactobacillus acidophilus (800 mg/kg) enhanced concentrations of GSH-Px, SOD and TAC in both serum and ileal tissue of growing rabbits. Similarly, Liu et al. (2019) confirmed that dietary supplementation of Clostridium butyricum improved the activities of SOD, GSH-Px, and CAT and minimized the MDA content in duodenum and ileum which are involved in preventing the oxidative damage of intestinal epithelium, leading to enhance the GIT health. Together, it could be documented that probiotics are involved in enhancing the antioxidative ability, activating the antioxidant enzymes, and suppressing the extra generation of ROS resulted in protecting rabbits against oxidative damage.
Probiotics have a positive effect on both innate (non-specific) and acquired (specific or adaptive) immunological response via stimulating macrophages, motivating phagocytosis of pathogenic bacteria, increasing cytokine production, and raising immunoglobulins (IgA, IgG, and IgM) concentrations in rabbits (Wang et al., 2017; Guo et al., 2017; El-Deep et al., 2021; Elbaz et al., 2023). The innate or nonspecific immune response is the first line of defence against numerous pathogens (Fathi et al., 2019; Al-Homidan et al., 2022). The vital mechanism of probiotics in nonspecific immunity relies on efficient physical and chemical barriers, such as healthy GIT epithelial cells and an effective mucus layer barrier, that prevent infections and pathogen multiplication (Ebeid et al., 2021 b). Wang et al. (2017) noted that dietary supplementation of Lactobacillus (1 × 109 CFU/g) increased serum concentration of IgG and IgM in growing Rex rabbits. Similarly, Guo et al. (2017) observed that rabbits supplemented with Bacillus subtilis (1.0 × 106 CFU/g) had higher serum concentrations of immunoglobulins (IgG and IgA), greater index of immune organs (thymus % and spleen %), and higher expression of the principal innate immunity genes participating in starting and regulating immune responsiveness, including IFN-γ, IL-1β, IL-4, IL-8, α-defensin, and β-defensin in rabbits. These cytokines and defensins play an important role in initiation and regulation of acquired immune responsiveness. Recently, Xia et al. (2024) observed that dietary heat-killed Lactobacillus acidophilus (800 mg/kg) reduced serum tumour necrosis factor-α (TNF-α) while elevating serum concentrations of immunoglobulins (IgA and IgM) and sIgA levels in the intestinal mucosa of growing rabbits. Wang et al. (2020) showed that dietary addition of 1.0 ×106 CFU Bacillus strains/g elevated the indexes of immune organs (thymus and vermiform appendix). Moreover, Fathi et al. (2017) also elucidated that dietary Bacillus subtilis (4.0 × 109 CFU/g) enhanced cell-mediated immunity at 48 h post-injection of phytohemagglutinin P (PHA-P) into the left ear in growing rabbits. Indeed, leukocytes (white blood cells) play a central role in innate or nonspecific immunity (phagocytosis and pro-inflammatory cytokines), which might be modified by addition of probiotics (Amri et al., 2020; Kadja et al., 2021). Amri et al. (2020) highlighted that oral administration of probiotics (Lactobacillus casei, Rhodopseudomonas palustris and Saccharomyces cerevisiae) increased the total number of leukocytes and neutrophils, and stabilized the absolute concentration of lymphocytes and monocytes in weaned NZW rabbits. Also, Kadja et al. (2021) observed that supplementation of probiotic mixture (Lactobacillus rhamnosus GG, Bifidobacterium animalis subsp. Lactis BB-12 and Saccharomyces boulardii CNCM I-745) increased the total number of leukocytes and the total number of neutrophils in growing rabbits. Several studies documented that probiotic supplementation enhanced the phagocytic activity and their phagocytic index in growing rabbits (Pogány Simonová et al., 2013, 2015; Lauková et al., 2016; El-Deep et al., 2021). These results were confirmed by Abdelhady et al. (2017) who reported that addition of Aspergillus awamori (0.05–0.15%) enhanced the immune response in the form of improving the phagocytic activity and phagocytic index as well as upregulating the inflammation-related genes including tumour TNF-α and IL-6. Then, these cytokines motivate the nuclear factor kappa beta (NF-κB) and its downstream target cyclooxygenase-2 (COX2) in growing rabbits. Collectively and by taking into consideration the antioxidative properties of probiotics and their role in GIT health, dietary probiotics are involved in stimulating the immune response and regulate production of cytokines in rabbits.
Probiotics boost growth through altering gut microbiome, enhancing gut histomorphology, activating the immune system, and triggering the release of many digestive enzymes (Liu et al., 2019; Wang et al., 2020; El-Deep et al., 2021). An enhancement in feed conversion ratio (FCR) and average daily feed intake (ADFI) are directly correlated with a rise in body weight gain (BWG), which is a measure of improved growth performance. In growing rabbits, dietary supplementation of probiotics increased BWG, ADFI, FCR, and production efficiency factor (Bhatt et al., 2017; Phuoc and Jamikorn, 2017; Guo et al., 2017; Wang et al., 2017; Kadja et al., 2021; Abdel-Wareth et al., 2021; Nwachukwu et al., 2021). Furthermore, in growing rabbits, Arram et al. (2018) pointed out that dietary probiotics have a positive effect on thyrotrophic hormones (TSH) and thyroid hormones (T3 and T4) which have a direct effect in accelerating metabolism leading to increasing the growth rate. They also highlighted that dietary probiotics have a positive effect on serotonin concentration, which is involved in improving appetite leading to increasing feed consumption. These findings are consistent with those of Elbaz et al. (2023) who documented that dietary Saccharomyces cerevisiae (5 g/kg diet) elevated serum values of T3 and T4 in NZW growing rabbits. Additionally, probiotics improved cecal fermentation and increased intestinal VFAs concentration that participate directly in covering energy requirements in rabbits (Phuoc and Jamikorn, 2017; Wang et al., 2020). Contrarily, other studies indicated that probiotics did not have a positive impact on rabbit productivity (Fathi et al., 2017; Tag El Din, 2019; Emmanuel et al., 2019).
Beneficial effects of probiotics on rabbit’s productivity and health
Summary of the beneficial effects of probiotics on rabbit’s productivity and health
| Probiotic | Level | Animal | Main impacts | References |
|---|---|---|---|---|
|
| ||||
| 1 | 2 | 3 | 4 | 5 |
| Saccharomyces cerevisiae | 5 g/kg diet | New Zealand White growing rabbits | Increased Lactobacillus count. | Elbaz et al. (2023) |
| Minimized E. coli count. | ||||
| Enhanced ileal villus height and villi height: crypt depth ratio. | ||||
| Improved all nutrients’ digestibility. | ||||
| Elevated serum values of thyroid hormones (T3 and T4). | ||||
| Enterococcus faecium NCIMB 11181 and Clostridium butyricum | 1 × 108and 2.5 × 106 CFU/kg diet | New Zealand White growing rabbits | Enhanced serum concentrations of total protein, globulin, IgM, and HDL-cholesterol. | Alagawany et al. (2023) |
| Improved cecal contents of total volatile fatty acids and propionic acid. | ||||
| Improved duodenal histomorphology parameters (greater villus height, greater muscular layer thickness, and lesser crypt depth). | ||||
| Improved growth performance traits. | ||||
| Saccharomyces cerevisiae and Bacillus subtilis | 1×108 CFU/g and 3×107 CFU/g | New Zealand White growing rabbits | Increased length of small intestine. | Helal et al. (2021) |
| Increased villus height and crypt depth. | ||||
| Reduced E. coli and Clostridium perfringens count. | ||||
| Increased Lactobacillus count. | ||||
| Aspergillus awamori | 100 and 150 mg/kg diet | APRI growing rabbits | Enhanced villi parameters (height and thickness). | El-Deep et al. (2021) |
| Enhanced digestibility coefficients of protein, lipids, and fibres. | ||||
| Improved the catalase activity and decreased malondialdehyde concentration. | ||||
| Improved average body weight and weight gain and decreased feed conversion ratio. | ||||
| Improved phagocytic activity and phagocytic index. | ||||
| Bacillus BSWJ2017001, BSWJ2017002, and BSWJ2017003 | 1.0 × 105– 1.0 × 107 CFU/g | Rex growing rabbits | Enhanced villus height and villi height: crypt depth ratio and decreased crypt depth in jejunum. | Wang et al. (2020) |
| Enhanced gut count of Lactobacillus and Bacillus, and reduced number of E. coli. | ||||
| Increased indexes of thymus and vermiform appendix. | ||||
| Improved serum concentrations of superoxide dismutase, glutathione peroxidase, and catalase. | ||||
| Reduced serum concentrations of malondialdehyde. | ||||
| Elevated caecal contents of acetic, propionic, and butyric acids. | ||||
| Enhanced activities of protease, amylase, and cellulose. | ||||
| Improved feed conversion ratio. | ||||
| Clostridium butyricum | 1.0 × 104– 1.0 × 105 CFU/g | Rex growing rabbits | Elevated the abundance of total bacteria, Ruminococcus albus, Ruminococcus flavefaciens, Firmicutes, Butyrivibrio fibrisolvens, Bacteroidetes, Clostridium cluster IV, Clostridium cluster XIVa, Lactobacillus, and Bifidobacterium in duodenum, jejunum, ileum, cecum, and colon. | Liu et al. (2019) |
| Increased height of villi and villi height: crypt depth ratio and reduced depth of crypts in small intestine segments. | ||||
| Increased relative expressions of MyD88, TLR2, and TLR4 and decreased pro-inflammatory cytokines (IL-6, INF-γ, and TNF-α). | ||||
| Increased secretory IgA (sIgA) in duodenum and ileum. | ||||
| Increased activities of superoxide dismutase, glutathione peroxidase, and catalase and reduced the malondialdehyde content in duodenum and ileum. | ||||
| Increased average daily weight gain. | ||||
| Lactobacillus acidophilus or mixture of Bacillus subtilis + L. acidophilus | 1×106 CFU/g or 0.5×106 CFU/g + 0.5×107 CFU/g | New Zealand White growing rabbits | Increased gut useful bacteria count (Lactobacilli and Bacilli), and decreased coliforms’ count. | Phuoc and Jamikorn (2017) |
| Improved body weight gain and feed conversion ratio. | ||||
| Improved digestibility coefficients of dry matter, organic matter, crude protein, neutral detergent fibre, and gross energy. | ||||
| Bacillus subtilis | 1.0 × 106 CFU/g | New Zealand White growing rabbits | Improved the relative abundance of Ruminococcus and reduced the percentage of Bacteroides and Clostridium at the phylum level. | Guo et al. (2017) |
| Enhanced the expressions of innate immune-related genes (nucleotide oligomerization domain 1 “NOD1”, NOD-like receptor C3 “NLRC3”) and NLRX1) in jejunum. | ||||
| Enhanced the expressions of innate immune-related genes (nucleotide oligomerization domain 1 “NOD1”, NOD-like receptor C3 (“NLRC3”) and NLRX1) in jejunum. | ||||
| Elevated serum concentrations of IgG and IgA. | ||||
| Increased thymus % and spleen %. | ||||
| Improved growth performance. | ||||
It is well documented that weaning is a critical period in young rabbits due to higher percentage of digestive disorders. Several nutritional strategies such as feed additives and feed restriction could be used to reduce the occurrence of digestive problems (in particularly epizootic rabbit enteropathy), and accordingly reducing both illness and mortality in growing rabbits (Tůmová et al., 2016, 2022 a, b). Interestingly, it was reported that probiotic administration enhanced the health condition and consequently lowered the mortality rate in rabbits (Pogány Simonová et al., 2013; Ayyat et al., 2018; Mancini and Paci, 2021). Recently, Li et al. (2024) documented that dietary inclusion of Enterococcus faecium ZJUIDS-R1 and Ligilactobaciiius animalis ZJUIDS-R2 (108 CFU/ml/kg/day) decreased bacterial diarrhoea via enhancing immune function (serum concentrations of IgA, IgG, and IgM) and restoring intestinal microbiota homeostasis (elevated the abundance of Ruminiclostridium 1, Adlercreutzia and Candidatus Saccharimonas and reduced the abundance of Shuttle-worthia and Barnesiella) in growing rabbits. Thus, it can be deduced that early stabilizing the GIT microbial balance via addition of probiotics is a successful strategy to minimize mortality rate during the most susceptible period of growing rabbits.
Published studies demonstrated that dietary probiotics enhanced semen quality characteristics and reproductive performance of rabbit bucks (Helal et al., 2018; Emmanuel et al., 2019). Besseboua and Ayad (2021) showed that administration of Saccharomyces cerevisiae (0.3 and 0.6 g/day/head) enhanced semen quality characteristics including the average semen volume, mass motility, and individual motility in rabbit bucks. Also, Emmanuel et al. (2019) observed that supplementation of Saccharomyces cerevisiae (0.12 g/kg) enhanced epididymal sperm characteristics (sperm concentration, motility and live sperm, tubule diameter, epididymal volume, volume fraction of duct, and total duct volume, but decreased testicular volume) and testicular morphometric traits (tubule diameter, epididymal volume, volume fraction of duct, and total duct volume) in NZW rabbit adult males. Helal et al. (2018) noted that dietary combination of 0.1% Bacillus subtilis + 0.1% live Saccharomyces cerevisiae enhanced physical semen characteristics (elevated volume, concentration, advanced sperm motility and reduced sperm abnormality and dead spermatozoa), serum testosterone concentration, initial fructose concentration in seminal plasma and the reaction time (libido) in NZW rabbit bucks. Moreover, Attia et al. (2013 a) showed that probiotic addition (1000 ppm of Lactobacillus acidophilus and Saccharomyces cerevisiae) ameliorated the negative effects of nitrate and improved semen quality characteristics in NZW rabbit bucks. It is important to mention that effect of probiotics on reproductive performance still needs further studies, especially in females.
Results concerning the effect of probiotics on carcass parameters and slaughtering yields, that are related to the final live BW, are frequently inconsistent. Numerous studies elucidated that probiotics supplementation enhanced carcass traits and edible parts in growing rabbits (Brzozowski and Strzemecki, 2013; Mohamed et al., 2017; Fathi et al., 2017). Mohamed et al. (2017) reported that dietary probiotics supplementation increased carcass weight, carcass %, heart weight, liver weight, kidneys weight, lungs weight, and giblets weight in broiler rabbits. On the other side, further studies indicated that probiotics had no significant impact on carcass traits in growing rabbits (Rotolo et al., 2014; Bhatt et al., 2017; Ayyat et al., 2018; Beshara et al., 2018; Abdel-Wareth et al., 2021).
The physico-chemical characteristics of meat are crucial in influencing its acceptability by consumers as well as its processing and storage capacity. Results illustrated the impact of probiotics on meat chemical composition and physical quality characteristics is inconsistent. Several studies showed that probiotics administration had no significant effect on proximate composition (protein, fat, ash, water and energy contents), pH48, colour, and water holding capacity of rabbits’ meat (Rotolo et al., 2014; Bhatt et al., 2017; Pogány Simonová et al., 2020). Contrarily, Fathi et al. (2017) showed that there is a significant impact of dietary probiotic supplementation on moisture, dry matter, organic matter, and ash content in rabbits’ meat. However, Pogány Simonová et al. (2016) indicated that dietary probiotics increased concentrations of phosphorus and iron and reduced concentrations of calcium and copper in rabbits’ meat. Abdel-Wareth et al. (2021) showed a reduction in water holding capacity and cooking loss in rabbits fed a mixture of fenugreek seeds and probiotics.
Rabbit production is often associated with several stress factors that lead to a decline in their productive and reproductive performance. Several scientific evidences indicated that most stress factors in rabbit production cause oxidative stress, which fatally damages the cell (Ebeid et al., 2023). Probiotics show their positive effects under stress conditions more than under ideal optimal conditions (Ayyat et al., 2018; El-Deep et al., 2020; Mohamed et al., 2023; Alagawany et al., 2023). Remarkably, dietary supplementation of probiotics alleviated the harmful impacts of heat stress in broiler rabbits (Fathi et al., 2017; Hegab et al., 2019; Alagawany et al., 2023). Ashour et al. (2024) reported that addition of Lactobacillus acidophilus from 5 to 13 weeks of age enhanced FCR, performance index (PI) values, and carcass traits during the summer season in growing NZW rabbits. Fathi et al. (2017) demonstrated that rabbits fed Bacillus subtilis (400 g/ton) improved carcass traits (carcass weight, dressing %, and cuts of mid part and hind part as a percentage of live BW), enhanced meat chemical composition (dry matter, organic matter, crude protein, and ash) and elevated cell-mediated immunity in growing rabbits raised in hot environmental circumstances. Similarly, Ayyat et al. (2018) noted that dietary Saccharomyces cerevisiae (3 g/kg diet) improved growth performance indices (LBW, DBWG, RGR, FI, and FCR), increased blood haemoglobin and red blood cells count, elevated serum concentrations of total protein, albumin, and globulin, and enhanced economic efficiency, but, respiration rate, rectal temperature, and heart rate were reduced in growing rabbits raised in hot summer conditions. Hegab et al. (2019) pointed out that dietary supplementation of Saccharomyces cerevisiae (3×109 CFU/kg) or Lactobacillus acidophilus (3×109 CFU/kg) heightened growth performance traits, reinforced the presence of beneficial yeast species (Yarrowia lipolytica), and blocked harmful bacteria (Salmonella spp., Clostridium spp. and Enterobacteria spp.) in NZW rabbits reared in heat stress circumstances. Alagawany et al. (2023) elucidated that supplementation of probiotics mixture (Enterococcus faecium NCIMB 11181 and Clostridium butyricum) had a positive impact on growth performance traits, immunological indicators (serum total protein, globulin, IgM, and HDL-cholesterol), cecal fermentation (cecal contents of total VFA and propionic acid), and duodenal histomorphology parameters (greater villus height, greater muscular layer thickness, and lesser crypt depth) in growing rabbits suffering from heat stress.
Indeed, mycotoxins are amongst the main feed-associated stressors in rabbit and poultry production and cause oxidative stress (Attia et al., 2013 b; 2016). Studies indicated that probiotics might be a useful approach in ameliorating liver oxidative damage caused by mycotoxins contamination (Abdelhady et al., 2017; El-Deep et al., 2020; Mohamed et al., 2023; Ebeid et al., 2024). Abdelhady et al. (2017) demonstrated that dietary supplementation of Aspergillus awamori (0.05–0.15%) ameliorated the negative effects of aflatoxin B1 via activating hepatic GSH-Px activity and minimizing MDA content of liver of growing rabbits suffering from aflatoxin B1 contamination. Also, Mohamed et al. (2023) postulated that different dietary kinds of probiotics had detoxification properties against aflatoxins B1 and improved growth performance (live BW, BWG, and FI) and nutrients digestibility coefficients (dry matter, organic matter, crude fibre, ether extract, nitrogen-free extract, and total digested nutrients) in growing NZW male rabbits. These data were consistent with those of El-Deep et al. (2020) who reported that addition of Aspergillus awamori (1 g/kg diet) alleviated the adverse effects of ochratoxin A and improved the phagocytic activity and phagocytic index as well as enhanced CAT and SOD activities in growing rabbits fed diets contaminated with ochratoxin A.
Globally, environmental pollutions pose a serious threat to human and animal health as well as productivity. Attia et al. (2018) indicated that probiotic administration (1000 ppm of Lactobacillus acidophilus and Saccharomyces cerevisiae) ameliorated nitrate toxification and improved FI and nutrient digestibility (dry matter, crude fibre, ether extract and crude protein) and reduced plasma urea concentration, and AST and ALT activities in NZW rabbit bucks. Also, Attia et al. (2013 a) showed that probiotic addition (1000 ppm of Lactobacillus acidophilus and Saccharomyces cerevisiae) relieved the negative effects of nitrate, improved semen quality characteristics (increased sperm concentration, total sperm yield, and total live sperm and reduced total dead sperms and total abnormal sperms), enhanced fertility %, number of offspring and total offspring weight and enhanced total antioxidant capacity in NZW rabbit buck.
As stated above, it might be concluded that probiotics may assist as a successful alternative to antibiotic growth enhancers in rabbit production under both thermo-neutral and heat stress circumstances. Dietary 1.0 × 104 – 1.0 × 106 Lactobacillus acidophilus, Bacillus subtilis, or Saccharomyces cerevisiae might be recommended for growing rabbits. The main profits of probiotics administration to rabbit diets is preserving a vigorous gut microbial equilibrium, supporting gut integrity, stimulating gut physiological function, boosting the gut immunity and health, improving the antioxidative properties, and triggering the host immune system, that subsequently appears as high performance and better resistance to diseases. Accomplishment of such profits is a requirement in rabbit industry.