Natural nutraceutical feed additives as antibiotic alternatives in rabbit production

Several studies showed the different impacts of using lactic acid bacteria such as Lactobacillus spp.; for instance, the daily BWG of rabbits fed on dried Lactobacillus (L.) acidophilus (9.6%) and yucca extract (12.1%) was better compared to control animals (Amber et al., 2004). Furthermore, the dietary supplementation of rabbits with a probiotic with Lactobacilli resulted in elevated serum levels of immunoglobulins (Ig)G and IgM and boosted cell-mediated immunity (Fathi et al., 2017; Wang et al., 2017). The results of Kadja et al. (2021) revealed that oral treatment of rabbits with a mixture of L. rhamnosus GG, Saccharomyces (S.) boulardii CNCM I-745, and Bifidobacterium animalis subsp. lactis BB-12 increased productivity (live BW and FCR), Ig levels, electrolyte concentrations, and reduced blood lipid concentration when compared with control non-treated rabbits. Nano-selenium enriched probiotic product containing Lactobacillus promoted alum adjuvanticity and enhanced antigen specific systemic and mucosal immunity (Liu et al., 2023). Lam and Jamikorn (2017) demonstrated that 28-day-old New Zealand White rabbits fed a probiotic containing Bacillus (B.) subtilis [1×10⁶ colony forming units (CFU)/g] and L. acidophilus (1×10⁷ CFU/g) showed increased BWG, greater growth, and better FCR than control without probiotics supplement. Similarly, El-Shafei et al. (2019) demonstrated that basal diets supplemented with 0.25 and 0.5 g of L. planterium (1×10⁶ CFU/g) induced positive and significant influences on BW, FCR, serum concentrations of triiodothyronine and thyroxine thyroid hormones, and IgG of 4-week-old New Zealand White rabbits.

Strains of Enterococcus (E.) faecium and durans (500 μl/animal/day) belong to lactic acid-producing bacteria which had antimicrobial and growth promoting effects (Simonová et al., 2016), and gut health promoting characters in 5-week-old Pannon White rabbits (Lauková et al., 2017; Simonová et al., 2020). Ammonia impairs the structural integrity of cecal tissues and reduces the levels of butyrate, acetate, and propionate in rabbit cecum (Cui et al., 2021). However, E. faecium (1 × 10⁸ CFU/kg diet) and Clostridium (C.) butyricum (2.5 × 10⁶ CFU/kg diet) reduced the cecal ammonia concentration (Alagawany et al., 2023), promoted immunological indicators, and induced a high serum lysozyme activity and complement component 3 in growing post-weaned rabbits subjected to heat stress (Bassiony et al., 2021). Moreover, feeding of 5-week-old New Zealand rabbits with C. butyricum (100 mg/kg diet) improved their intestinal morphology, gut microbiota, and growth performance when compared with rabbits fed on basal diet (Huang et al., 2021), as well as enhanced IgA production and preserved intestinal barrier function (Liu et al., 2019 a). On the other side, Simonová et al. (2009) found no effect on the quality of rabbit meat after treatment with bacteriocinogenic and probiotic strain E. faecium CCM 4231. The drinking water treatment of heat-stressed 28-day-old weaned New Zealand White rabbits with Pediococcus (P.) acidilactici (CNCM I-4622) (1 × 10¹⁰ CFU) enhanced the BWG and feed efficiency and controlled some physiological functions (respiratory and heart rates and rectal temperature), without effects on the weights of viscera, digestive tract, and edible parts when compared with animals fed on basal diets without treatments (Ayyat et al., 2018).

Gram-positive spore-forming bacteria of the genus Bacillus that do not colonize the intestinal tract of animals, are often used as probiotics. They produce enzymes and vitamins and have antioxidant and antimicrobial effects (Milián et al., 2017). For instance, B. cereus showed positive impacts on performance and health of growing rabbits and modulated the immune response against infections (Trocino et al., 2005; Guo et al., 2017; Helal et al., 2021). Moreover, Phuoc and Jamikorn (2017) found that a probiotic supplement containing B. subtilis (0.5 × 10⁶ CFU/g) plus L. acidophilus (0.5 × 10⁷ CFU/g) enhanced feed efficiency, BW, and microbial population of 28-day-old weaned New Zealand White rabbits when compared with groups fed on basal diet without a probiotic supplement (control). Similarly, the inoculation of growing rabbits diets with 8% fermented rapeseed meal with B. subtilis strain 87Y significantly improved BW, average daily BWG, and FCR, as well as red blood cells, hematocrit, hemoglobin, and mean corpuscular volume blood profile when compared to the control group (Czech et al., 2024). Moreover, the same study indicated a significant decrease in the plasma levels of the low-density lipoprotein (LDL), the ratio of total cholesterol to high-density lipoprotein (HDL), and triacylglycerols (Czech et al., 2024).

The dietary inclusion of S. cerevisiae for rabbit feeding resulted in promoted general conditions in terms of enhanced digestibility, feed efficiency, growth rate, performance, and meat production, along with reduced gut pathogenic bacteria (Ezema and Eze, 2012; Garcia-Mazcorro et al., 2020; Helal et al., 2021; El-Sawy, 2022). Ayyat et al. (1996) reported that incorporated diets of lactating New Zealand White rabbit does with live yeast (Lacto-Sacc) (0.1%) helped in increasing milk production, litter size, and weight of 21- and 28 day-old weaned offspring. Similar results were obtained by Belhassen et al. (2016) who found high fertility rate of New Zealand × Californian rabbit does and improved viability rate of litter at birth following treatment of rabbits with live S. cerevisiae (6.5 × 10⁹ CFU/kg feed). The addition of S. cerevisiae var. boulardii in growing rabbits feed might promote the growth of gut lactic acid fermenting bacteria and enhance the digestibility of feed and utilization of ammonia (El-Sawy, 2022). On the other side, inactivated S. cerevisiae shows more action uniformity and direct accessibility of vitamins or other growth factors to the microbiota than living cells yeast (Opsi et al., 2012). The dietary treatment of 5-week-old New Zealand White male rabbits raised under hot summer conditions with organic selenium (0.3 mg/kg diet), inactivated S. cerevisiae (1000 mg), or their combination resulted in enhanced FCR, antioxidant activity, and gut health when compared with diets containing antibiotic colistin (120 mg/kg diet) or a control basal diet (Al-Sagheer et al., 2023). However, Rotolo et al. (2014) reported that the addition of different levels of live S. cerevisiae var. boulardii (300 and 600 mg/kg) to rabbit diet did not affect meat physicochemical characteristics from 37 to 84 days of age. Sarat Chandra et al. (2015) also demonstrated no differences between the cholesterol contents of rabbits when fed with S. boulardii (50%) and P. acidilacticii (10⁹ CFU/g of feed).

Although probiotics improve the rabbit health and have several beneficial health activities (Alagawany et al., 2023), their effectiveness, functionality, and safety have become debatable (Kothari et al., 2019). In this respect, probiotics did not show any observed positive influences on the carcass or organ traits of the treated rabbits (Bhatt et al., 2017; Ayyat et al., 2018). Also, the risk of inflammatory response, infection, or microbial translocation has been associated with using different probiotics (Gueimonde et al., 2013). Besides, some post-weaning digestive problems with a fragile gut function may occur due to the unique physiology of the gut (Colombino et al., 2022). The discrepancy in the obtained results may be related to the differences in their administered dosage or inclusion rates, animal species, study population, used strain of the compound, and composition of diets.

Synbiotic is a mixture of probiotics and prebiotics that beneficially affects the host by enhancing the survival and establishment of live microbial dietary supplements in the gut, by selective stimulation of the growth and/or activation of the metabolism of one or a limited number of health-promoting microorganisms, and therefore improving host welfare (Gibson and Roberfroid, 1995). The term “synbiotic” implies synergy, as prebiotic component selectively favors a probiotic microorganism. Different formulas containing both synbiotics are used in animal nutrition.

The dietary supplementation of rabbits’ diets with synbiotics resulted in enhanced growth and production performance (Oso et al., 2013; Hassanin et al., 2015; Ali and Hassan, 2018; Kurchaeva et al., 2020; Chinwe et al., 2021). The presence of lactic acid bacteria with their metabolites in fermented probiotic components or synbiotics, along with other short-chain organic acids, proteolytic enzymes and phytase, could enhance the gut microbiota, promote amino acids and minerals absorption, and modify some hematological and lipid parameters (Wlazło et al., 2021 b). Moreover, rabbits fed on diets containing fermented rapeseed meal showed an increase in plasma IgA, while a decrease in intestinal percentage of potentially pathogenic bacteria such as Clostridium spp. and Escherichia coli (E. coli) (Wlazło et al., 2021 a). According to Abdelhady and El-Abasy (2015), the dietary inoculation of rabbits with a prebiotic (MOS) (1 g/kg feed), a probiotic (Bacillus spp.) (0.4 g/kg feed), and their mixture resulted in improvement of BWG and FCR, stimulation of cell-mediated immune response and liver and kidney functions, as well as reducing the adverse impacts of Pasteurella multocida infection in 5-week-old New Zealand White male rabbits.

Forty-day-old growing rabbits fed on diets containing alginate encapsulated synbiotics [S. cerevisiae (11 × 10¹²) and Moringa oleifera (M. oleifera) leaf extract (0.15 g)] showed increasing lactic acid bacteria and yeast populations and decreasing cecal pathogenic bacteria and pro-inflammatory and oxidative stress, thus stimulating phagocytic and lysosomal activity (Hashem et al., 2020). Similarly, Hashem et al. (2021) found that nano-encapsulated alginate-synbiotic had positive influence on BWG and FCR of growing rabbits in comparison to non-treated control animals. In addition, synbiotics played an important role in alleviating the negative impacts of heat stress on rabbit health and production profit (Ebeid et al., 2023). Synbiotic supplementation of rabbits may possibly improve gut microbial population and digestion resulting in enhanced feed efficiency, BWG, and performance index of heat-stressed rabbits (Ebeid et al., 2023). Whereas Ewuola et al. (2011) found that dietary treatment of basal diets with a prebiotic (4 kg/ton), a probiotic (500 g/ton), or their combinations could improve the growth performance indices and nutrient digestibility, but did not affect the carcass characteristics of 56-day-old weaned rabbits. The authors referred the last result to the doses of the used probiotic and prebiotic, animal species, age, weight, or breed, strains of the used microorganism, and composition of diets.

Rabbit meat is a lean, low-fat, high-protein food beneficial for human health, providing essential B vitamins (B₁₂), iron, and minerals such as phosphorus, zinc, and magnesium, while also being low in cholesterol and sodium. For instance, Czauderna et al. (2021) found improvement in meat nutritive value of 35–90-day-old New Zealand White rabbits after supplementation with lycopene. In addition, rabbits fed a high-fat diet and lycopene showed reduced lipid parameters with a potential protective effect against oxidative damage (Rane et al., 2019; Imbabi et al., 2023). However, the addition of lycopene (carotenoid in tomatoes; 100 and 200 mg/kg diet) and allicin (organosulfur compound in garlic; 100 and 200 mg allicin/kg diet) showed no considerable effect on FI, live BW, or the hematology profile in 5-week-old V-line rabbits, but the FCR was improved as compared with non-treated control animals (Zweil et al., 2016).

Several studies demonstrated that growing rabbits fed on M. oleifera dry leaves showed improved performance indices (BW, BWG, and FCR) (El-Badawi et al., 2014; El-Kholy et al., 2018; Hashem et al., 2019; Mohammed et al., 2020). High carcass percentage and dressing percentage, as well as low abdominal fat weight were also observed following supplementation of rabbits with M. oleifera (El-Kholy et al., 2018; Omara et al., 2018; Nayel, 2021). In addition, growing rabbits supplemented with moringa leaves diets showed decreased concentrations of malondialdehyde (MDA), but increased total antioxidant capacity, which could be attributed to reduction of fat deposition by either prompting the hormone-sensitive lipase activity in fat tissue or reducing lipoprotein lipase and malate dehydrogenase activities (El-Badawi et al., 2016; Ojo and Adetoyi, 2017). The reduced fat content in the abdomen of rabbits after feeding on moringa could be linked to the ability of this plant to enhance the growth of beneficial bacteria such as Lactobacillus spp. that limit the activity of acetyl-CoA carboxylase and the synthesis of fatty acids. Furthermore, the addition of M. oleifera extracts in the drinking water of growing rabbits had positive influences on serum biochemical responses without any adverse effects on kidney and liver functions (El-Kholy et al., 2018). An improvement in the serum lipid profile (cholesterol, triglycerides, and LDL) of rabbits fed on M. oleifera leaves extracts were also reported (El-Kholy et al., 2018; Selim et al., 2021; Reda et al., 2025). Regarding the effects of M. oleifera on the immune response, some constituents such as polyphenols and flavonoids have strong immuno-stimulant activities (Amaglo et al., 2010). Boosted immunity and enhanced liver function parameters in the M. oleifera leaves-fed rabbits were linked to the higher levels of total protein and globulin and lower levels of alanine transaminase (ALT) and aspartate transaminase (AST) in serum (Selim et al., 2021; Reda et al., 2025). Also, the daily oral treatments of rabbit does with 10 and 25 mg of nano-encapsulated M. oleifera extracts/kg BW for 75 days induced an enhancement of BW, FI, glucose concentration, white blood cell counts, phagocytic activity, lysozyme activity, concentrations of IgG and colostrum Ig, milk yield, conception and parturition rates, and litter characteristics than control free M. oleifera treated rabbit does (El-Desoky et al., 2022). It has been shown that the addition of M. oleifera leaves extracts in the drinking water for growing rabbits augmented the microbial ecology of the gut and decreased the count of pathogenic bacteria such as E. coli and Clostridium spp. (Aljohani and Abduljawad, 2018; El-Kholy et al., 2018; Reda et al., 2025). El-Desoky et al. (2021) demonstrated that the nano-encapsulated M. oleifera leaf ethanolic extract (25 or 10 mg/kg BW) had many active ingredients with antimicrobial and/or anticoccidial activities such as salinomycin, rifabutin, 2-furoic acid, lactacystin, and 9S, 11, 15 S-trihydroxythrombox-13E-enoic acids which inhibit the growth of pathogenic bacteria by disturbing the cell membranes or essential enzymes synthesis in the inoculated rabbits does.

Feeding of rabbits on a diet containing a mixture of compound fennel (Foeniculum vulgare), lupin (Lupinus albus L.), fenugreek (Trigonella foenum-graecum L.), and khartoum (Cassia senna L.) resulted in antimicrobial effects against C. coccoides and C. leptum in rabbits as well as anti-inflammatory, immunomodulatory, and antioxidant impacts (Dalle Zotte et al., 2016). Feed treatment of weaned Moshtohor rabbits with fennel oil (1 ml) as a natural alternative for gentamycin (1 ml) improved daily BWG and FCR via enhancing the intestinal villus length and mucus thickness and meat shelf-life, but decreased the oxidative stress by increasing the antioxidant enzymes (Imbabi et al., 2021). Similar results were obtained by Omer et al. (2013) who demonstrated an enhancement in BW of 5-week-old weaned rabbits after feeding on diets supplemented with fennel seeds (0.5%) and oregano (0.5%) when compared with basal diets without treatments. Elghalid et al. (2020) demonstrated that a mixture of herbal plants and spices containing fennel (0.5 ml or 1 ml/liter of the drinking water) increased HDL cholesterol and triglycerides, while decreased MDA in the treated V-Line rabbits as compared with non-treated control rabbits. Because the additives mixture may contain phenolic compounds that elicit antioxidant action by scavenging reactive oxygen species, enhancing cellular antioxidant enzymes (e.g., superoxide dismutase, catalase, and glutathione peroxidase), and increasing glutathione, the fennel essential oil increased HDL, cholesterol, and triglycerides, but decreased MDA (Elghalid et al., 2020). In addition, rabbits fed on diets containing essential oil of fennel seeds showed reduced oxidative stress by increasing the levels of the antioxidant enzymes and inhibiting lipid peroxidation (Imbabi et al., 2021). It has been reported that Funiculus vulgare could decrease ALT, alkaline phosphatase, and AST in the serum of treated rabbits (Nazir et al., 2020). El-Hammady and AbdelKareem (2015) also reported a significant improvement in the number of mating per conception and conception rate in rabbit does fed a diet supplemented with dried herbal seeds (50% fenugreek, 30% caraway, and 10% each of fennel and dill). In contrast, no differences were found in carcass traits of rabbits fed with 20% and 40% fennel seed meal instead of clover hay and a commercial enzyme mixture (0.35 g/kg diet) (Salama et al., 2019). Also, Benlemlih et al. (2014) found that dietary supplementation of 35-day-old New Zealand White rabbits with fennel oil (0.05%) and thyme oil (0.05%) as well as oxytetracycline (1 g/liter drinking water) did not enhance live BW, growth rate, and FCR or the cecal count of E. coli and C. perfringens.

Bee products were found to improve the reproductive parameters of rabbits (Suleiman et al., 2021; Abd El-Ghany, 2024 a). The beneficial effects of bee pollen feed additives on BW, BWG, FI, and FCR ratio as well as pancreatic enzymes and intestinal contents of lipase, amylase, and protease activities in rabbits were reported (Zeedan and El-Neney, 2014; Zeedan et al., 2018; Abdel-Hamid and El-Tarabany, 2019). Likewise, Sierra-Galicia et al. (2023) found that supplementation of rabbits with bee pollens increased average daily BWG, and hot carcass yield, however, decreased FI, FCR, serum creatinine, ALT, and AST levels. The phenolic compounds in honey bees (catechin, caffeic acid, and vanillic acid) and in bee pollens (hesperidin, cinnamic acid, apigenin, rutin, chlorogenic acid, and kaempferol) showed antioxidant, digestive, antimicrobial, immuno-stimulatory, nutraceutical, and growth promoting activities (Bakour et al., 2022). El-Hammady et al. (2017) found an increase in serum protein and albumin in 52-week-old V-line and Moshtohor rabbit bucks provided with bee pollen at levels of 500 and 1000 mg/buck. Besides, incorporation of 2.6-year-old New Zealand rabbits’ doe diets with bee pollen (1 g) resulted in higher conception rate and milk production, larger litter size, and more increase in offspring growth performance compared to control non-treated rabbits (Dias et al., 2013). In the same line, Attia et al. (2015) reported that administration of bee pollen and/or propolis (200 mg/kg BW) or inulin and/or MOS (35 mg/kg BW) resulted in fewer services per conception but greater fertility rate in nulliparous V-line female rabbits compared to the control group. Moreover, honey bees treatment at a level 2 g/kg BW enhanced metabolic attributes of carbohydrates and lipids in a local breed of alloxan induced diabetic male rabbits compared to control non-treated animals (Shikoo and Bakeel, 2021). Ten days before mating and 28 days during pregnancy, treatments of 5-month-old Californian does with 3 ml of distilled water containing bee pollen (200 mg), honey bee (0.2 ml), date palm pollen (200 mg), and their mixture/doe/day improved the reproductive performance over the control distilled water receiving group (El-Speiy et al., 2024 a). This improvement may be attributed to augmentation of oogenesis, oocytes, hormone regulation, increasing pregnancy rate, and prevention of uterine rupture (Shehzad et al., 2021). Likewise, doe rabbits given two levels of date palm pollens (250 and 500 mg/doe) showed increased levels of estrogen, progesterone, and prolactin, enhanced ovulation rate, litter survival rate, pregnancy rate, and litter weight at birth and weaning (Baagar et al., 2022).

Incorporation of mulberry (Morus alba) leaves in rabbit diets resulted in positive impacts on growth performance, meat quality, and intestinal morphology, which led to reduced production costs and increased farm profitability (Khan et al., 2019, 2022). Morus alba leaves successfully replaced 50% of concentrate in rabbit diet and helped in the enhancement of growth performance and prevention of meat lipid peroxidation without any adverse effects on organoleptic characteristics (Khan et al., 2020). Nigella sativa L. seeds oil (200–400 mg/kg BW) showed a good therapeutic effect against hepatic coccidiosis in 6–8-week-old local male rabbits (Rafid et al., 2015). Feeding of 4-week-old male V-line rabbits with lettuce (Lactuca sativa) fertilized with whey protein hydrolysate improved body weight, carcass weight, and meat shelf-life compared to those that received nitrate-fertilized lettuce due to the high content of polyphenols and flavonoids (Osman et al., 2021). El-Deep et al. (2021) found that Aspergillus awamori at a concentration of 100–150 mg per kg BW showed a significant improvement in the average BW and BWG, protein, lipid, and fiber digestibility coefficients, antioxidative activity, as well as hemoglobin, total protein, red blood cell count, and phagocytic activity and index of 3-month-old male APRI rabbits compared with the control group. Rosemary and ginger essential oils at doses of 0.25% and 0.5% for each supplementation significantly improved BW, BWG, average daily gain, and FCR, increased weight percentages of liver and giblets, enhanced the total antioxidant capacity, but decreased cholesterol and thiobarbituric acid levels in meat of 42-day-old New Zealand White rabbits compared to the control (Elazab et al., 2022). Moreover, El-Deep et al. (2020 b) showed basal diets supplemented with chicken egg lysozyme at levels of 50, 100, and 200 mg/kg had positive impacts on the growth performance, FI, FCR, intestinal Lactobacilli count, hematological parameters, lymphocyte count, total protein and globulin concentrations, serum biochemical parameters, and resistance against E. coli and Clostridium spp. in 5-week-old APRI line-rabbits’ cecum relative to control non-treated groups. A basal diet incorporated with garden cress seeds at levels of 3%, 4.5%, and 6%, respectively enhanced the litter weight, milk yield, lipid profile parameters, and total antioxidant and superoxide dismutase activity of heat-stressed 6-month-old V-line does (El-Gindy et al., 2022). The commercial diets containing garlic extracts (50, 75, and 100 mg/kg) or turmeric (30, 60, and 90 mg/kg) significantly promoted ear temperature, respiration rate, germ cell apoptotic number, total cholesterol, triglycerides, malondialdehyde level, libido, semen and sperm quality, hemoglobin, red and white blood cells, platelets, and total antioxidants capacity of buck rabbits under heat stress (El-Kholy et al., 2021). Additionally, the substitution of soybean meal protein by jojoba treated with L. acidophilus at levels of 10%, 20%, and 30% improved nutrient digestibility, dressing percentage, and lipid profile in 5-week-old rabbits versus control animals (El-Adawy et al., 2013). Similarly, the dressing percentage of rabbits fed potato vines treated with L. acidophilus was increased compared to control non-treated groups (El-Banna et al., 2010). Nevertheless, Olorunsogbon et al. (2022) demonstrated that the addition of aqueous extract of ginger (Zingiber officinale) (50%) and almond fruit (Terminalia catappa) (50%) to the drinking water of weaned rabbits did not induce any change in the hematological parameters and blood biochemistry.

Regarding the uses of butyric acids in rabbit farming, Carraro et al. (2005) observed that diets supplemented with butyrate at levels of 0.5, 1.0, and 2.0 g/kg resulted in a greater increase in FI and average daily BWG, but a decrease in dry matter digestibility compared to a control diet without treatment. Similarly, Hullar et al. (1996) found improvements in 10-week-old rabbits’ performance and coefficients of apparent total tract digestibility following the addition of 0.15% sodium butyrate to the diet for 4 weeks. Supplementation of rabbits during the growing-fattening period with coated sodium-butyrate reduced FI, daily BWG, but enhanced the FCR (Ribeiro et al., 2012; Hassanin et al., 2015). Moreover, villus height and width were not affected, but crypt depth was increased in the treated rabbits. Hassanin et al. (2015) demonstrated significant improvements of BW, FI, cecal fermentation, intestinal morphometry, and metabolic profile in growing New Zealand buck rabbits after dietary supplementation with coated sodium butyrate (500 g/ton feed) and/or synbiotic (500 g/ton feed). Besides, formic acid together with lactic acid enhanced the feed efficiency and average daily BWG in 30–55 and 56–84-day-old rabbits (Cesari et al., 2008).

The addition of citric acid to rabbits’ diets increased carcass weight (Abdel-Khalek et al., 2012), improved immune response, enhanced nutrient digestibility (Debi et al., 2010), and reduced weaning fatigue (Li et al., 2009). On the other side, organic acids with probiotics did not show significant improvement of weaning rabbit performances (Hollister et al., 1990; Scapinello et al., 2001). Similarly, no detectable effect on growth rate (Skřivanová and Marounek, 2002), or digestibility coefficients (Abecia et al., 2005) was observed following supplementation with caprylic acid (2 and 5 g/kg) and fumaric acid (5 and 10 g/kg), respectively. Moreover, the antimicrobial activities of sodium butyrate (0.5, 1.0 and 2.0 g/kg) (Carraro et al., 2005), fumaric acid (Scapinello et al., 2001), or formic acid (5 mg/ml) (Skřivanová and Marounek, 2007) were not detected in the treated rabbits. The discrepancy of the different effects of acids on health or performance depends on the applied specific acid, dosage, and type of rabbits.

Lalhriatpuii and Patra (2022) demonstrated that rabbits fed on 10% to 20% fermented rice showed an improvement in the feed uptake and nutrient utilization compared to the non-treated group. Also, Oloruntola et al. (2018) revealed that dietary addition of multi-enzymes at dosage of 0.35 g/kg improved the final live BW and total and daily BWG of rabbits when fed with liquor fermented cassava peels based diets. Fermented feed compounds could support the endogenous phytase activity and enhance better nutrient utilization in the rabbit digestive tract. Rabbits can break down phytin complexes in cecum more than half of the phytase activity (Marounek et al., 2009). Moreover, the improved protein availability may be affected by the presence of other extracellular degradative enzymes including cellulases, proteases, glycosidic hydrolases, hemicellulases, and peroxidases in the fermented feed (Shi et al., 2016). The fermentation process also decreases the amount of antinutrients (Vig and Walia, 2001) and improves the nutrient availability (Koo et al., 2018). Some components such as phenolic substances, bioactive peptides, lactic acid, β-casomorphins, gamma-aminobutyric acid, and short-chain saturated fatty acids are present in the fermented feed with health-promoting effects (Karwowska and Kaczmarczyk, 2023).

Several studies showed that the addition of multi-enzymes such as phytase, protease, cellulase, α-amylase, β-glucanase, and lipase for rabbits to rabbit diets could degrade fibers and proteins, increase digestibility, and consequently improve productive performance and meat quality (Bolis et al., 1996; Fernandez et al., 1996; Sarhan, 2001; El-Mandy et al., 2002; García et al., 2005; Oloruntola et al., 2018; Abdullahi et al., 2020; Abu Hafsa et al., 2022). The study of Abdl-Rahman et al. (2010) showed that multi-enzymes-bentonite co-supplementation has a positive influence on cecal fermentation and metabolic pattern in rabbits. The average daily FI of growing California rabbits was increased due to supplementation of a compound containing xylanase, protease, cellulase, hemocellulase, and amylase at levels of 500 or 750 mg/kg feed (Makled et al., 2005). The drinking water supplementation of 35- to 40-day-old growing New Zealand White rabbits with multi-enzymes (0.5 ml/liter) resulted in a greater improvement in BW, daily BWG, and FCR as compared with high dietary levels (16 and 19%) of crude fiber (Ibrahim, 2000; Abd El-Latif et al., 2008). Similar results were obtained by Eiben et al. (2004 b) who found an enhancement in FCR and reduced mortality rate in weaning rabbits fed cellulase supplemented diets. Moreover, Gutierrez et al. (2002) found that daily BWG of rabbits was increased by 3.1% as a result of including xylanase and pectinase exogenous enzymes in the diets. The addition of probiotics and multi-enzymes to the rabbit diets improved BW, BWG, and FCR (El-Sagheer and Hassanein, 2014). For instance, Chandra et al. (2014) demonstrated significant impacts of incorporation of probiotics (S. boulardi and P. acidilacticii, 50% each) and an enzyme mixture (fibrolytic, proteolytic, and lipolytic) alone or in combination on BWG of rabbits. Likewise, treatment of sugarcane bagasse with L. acidophilus, exogenous enzymes, or their combination successfully improved FCR, blood chemical composition, carcass characteristics, growth and feed efficiency parameters, and economical evaluation of the fed rabbits (Abdel-Aziz et al., 2015). Besides, feeding rabbits on diets containing enzymes and a phytobiotic Alchornea cordifolia leaf meal also enhanced the digestibility of crude protein and crude fiber (Ayodele et al., 2016). The replacement of rumen liquor fermented cassava peels in rabbit diet can be increased beyond 50% by multi-enzyme supplementation (Oloruntola et al., 2016). However, no significant effect on performance following dietary supplementations of rabbits with enzymes was observed (García-Ruiz et al., 2006). Kong et al. (2022) reported that there was no positive influence of feeding Rex rabbits on enzymolytic soybean meal. Also, feeding of growing rabbits on diets containing 10% corn cobs and enzymes preparation containing cellulase, β-glucanase, α-amylase, protease, and lipase induced no adverse effects on growth performance parameters (Abaza and Omara, 2011).

Regarding the effects of enzymes on carcass traits, Shanmuganathan et al. (2004) demonstrated that some exogenous enzymes (cellulases and proteases at 400 ppm), yeast culture (Yea-Sacc1026 at 200 ppm), or effective microorganisms (1%) enhanced the carcass yield (24.7%) of 8- to 9-week-old New Zealand White rabbits due to better nutrient utilization when compared with basal diet treated control rabbits. Nonetheless, no differences were found in carcass traits of rabbits fed with 20% and 40% fennel seed meal instead of clover hay and a commercial enzyme mixture (0.35 g/kg diet) (Salama et al., 2019). Similarly, Hernández-Martínez et al. (2018) found that Trametes maxima and Pycnoporus sanguineus hydrolyzed sorghum (300 g/kg diet) lowered feed and water intake without affecting carcass traits or chemical composition of 20-day-old New Zealand rabbits. Results may suggest that the synthesis and assimilation of nutrients in muscles are more efficient when diet ingredients are hydrolyzed before being consumed by the rabbits. Although doses of 20,000, 40,000, and 60,000 IU/kg¹ of laccase enzymes from the spent substrate of Pleurotus ostreatus enhanced productive performance of 35-day-old California × English Spot rabbits, they deteriorated rabbit meat characteristics by increasing the treatment concentrations (Saavedra-Castillo et al., 2023). Furthermore, the effects of using multi-enzymes on blood parameters were studied by Veselin et al. (2003) who showed no significant changes in the levels of albumin and globulin of 6-month-old New Zealand rabbits fed on multi-enzymes (1 g/kg diet) in the concentrate mixture. Although exogenous enzymes can increase the digestibility of fibers and improve the nutrients availability to complement endogenous enzyme activity (Ojha et al., 2019), the high cost and accessibility may limit their use.