Global demand for rabbit meat continues to escalate, as it is an alternative to broiler chicken rearing. Interestingly, worldwide rabbit population exceeds 1 billion, with China, Italy and Spain leading as major producers (FAO, 2023) of rabbit. As per the FAOSTAT (2014), in 2012, global rabbit meat production increased to 1.83 million tons. Rabbit meat is considered as lean due to very low level of intramuscular fat and as an alternative to broiler chicken due to its higher protein (20-21%) and low fat content (10-11%), when compared with meat from other species.
       
Usage of antibiotic growth promoters in livestock nutrition (Windisch et al., 2008) for the improvement production performance was completely prohibited, as they might result in resistance to antibiotics and the antibiotic residues could be present in products of animal origin intended for human consumption. Due to this ban, presently, the livestock owners are using probiotics in feed to its role in reducing early mortality rates, improving feed conversion efficiency (Elmasry et al., 2021) and enhancing the activity of digestive enzymes while maintaining microbial balance in the digestive tract (Soomro et al., 2019).
       
In Tamil Nadu, rabbit farming is widely based on locally available feed resources including natural grasses, legume leaves, wild vegetables and agro industrial byproducts which have a very important role for rabbit production. The diet for rabbits usually contain high proportion of fiber and low protein content. Paragrass, also called buffalo grass, is a perennial fodder crop that spreads through stolons and is found in tropical countries like India, Africa and Australia, mostly in wet and swampy areas near rivers, lakes and dams and it is valued as a natural fodder rich in dietary fibre. However, using solely para grass in the diets could reduce the growth rate of rabbits due to its higher dietary fiber content and similar negative growth rate was also observed in our pilot study of treatment groups fed with paragrass alone. The soluble fiber fraction serves as a prebiotic and may have synergistic effects with probiotics (Wong et al., 2006) and thus, offer improvement in nutrient digestibility and stimulate growth of rabbits. Different levels of probiotic inclusion can influence carcass traits such as dressing percentage, muscle deposition and fat content, while also enhancing meat quality attributes like tenderness, juiciness and nutrient composition. (Abdel-Wareth and Lohakare, 2014; Al-Saef, 2017)
       
Moreover, the synergetic effects of probiotics and paragrass in rabbits have not been reported consistently in previous studies and also not been focused to improve animal health, particularly improving the carcass characteristics and meat quality of rabbits. The study was, thus, conducted to evaluate the efficacy of different level of probiotic supplementation on the carcass characteristics and meat quality in Soviet Chinchilla rabbits under cage system of housing.

Location of study
 
The present study was conducted at the Rabbit Section, Livestock Farm Complex, Madhavaram Milk Colony, Chennai-600 051, which is located at 13.15^oN latitude and 80.24^oE longitude, with an elevation of approximately 8 m above mean sea level. In this region the maximum temperature is about 38^oC, while the minimum is around 21^oC and an average relative humidity of about 71%. The area receives an annual rainfall of around 1,336 mm.
 
Details of experimental animals and duration of study
 
A total number of twenty four (comprising of both the sex) growing soviet chinchilla rabbits with an average body weight of 850±50 gm, 60 days of age, were randomly assigned to four dietary treatment groups (n=6 irrespective of sex). This study was conducted during the year 2023-2024.
 
Animal management
 
Experimental rabbits were reared individually in cages of galvanized wire net (width x length x height: 60 cm x 60 cm x 40 cm) equipped with automatic drinker and a manual feeder. Ambient temperature was maintained at 22^oC with a 12 h light/dark cycle. The rabbits were housed under the similar managerial, hygienic and environmental conditions. Every rabbit, was provided with sufficient fresh drinking water. The details of green fodder, concentrate feed, different levels of probiotic supplementation for the experimental rabbits were mentioned in Table 1.


 
Details of experimental groups
 
The first group was fed with paragrass and concentrate (T₁), paragrass and concentrate mixed with probiotics at 0.05% (T₂), paragrass and concentrate mixed with probiotics at 0.1% (T₃) and paragrass and concentrate mixed with probiotics at 0.2% (T₄) respectively for three months. The probiotics levels were selected based on company recommendations (Healthy gutTM probiotics for rabbit, Equa Holistics manucature, Athens) and contains a unique and balanced mix of lactic acid bacteria culture, (P. freudenreichii, P. shermani, E. thermophilus, L. lactis, L. casei, B. longum, P. acidilacti, P. pentosaceus, B. bifidum, B. animalis, L. brevis, L. fermentum, L. acidophilus, L. plantarum, S. cerevisiae) fermentation extract of freeze dried probiotic organism, in a high concentration that adds to the count and assist in maintaining a healthy microflora which helps maximize feed digestion and utilization and prevent digestive upsets as well as contains a unique balanced combination of the was used for study. Probiotics at different level were mixed separately in 1 kg of the concentrate and were added to the required feed amount for the prescribed experimental period. Throughout the whole experimental period (three months), rabbit diets were formulated to meet the standard nutritional requirements for growing meet type rabbit. The ingredients used and chemical composition of green fodder and concentrate feed provided for the experimental diets are mentioned in Table 1 and 2. Six rabbits from each group were slaughtered at five months of age. The carcass characteristics, edible and inedible offals (%), Intestinal villus morphology, carcass measurements, Cut-up parts (%) and meat quality characteristics were recorded and evaluated as per the standard procedure.


 
Carcass characteristics, offals yield, carcass measure-ments and cutup parts yield
 
At the end of three months of experimental feeding, all the rabbits were slaughtered after starving them for 12 hours by Halal method (Ramayyan et al., 1980). The carcass was split into different cuts-two shoulder, thorax, loin, abdominal flap, rump and hind leg. The two legs were separated by sharply cutting across the carcass immediately in front of hip joint. The loin was separated from the chest at the last rib. Two shoulders were removed from the thorax by separating muscles between scapula and ribs. The weight of primal cuts was expressed as percentage of hot carcass weight. The cut up parts were measured for its length and circumference and expressed in centimeter. The weight of blood, different parts (head, skin, feet and carcass), edible (liver, heart and kidney) and inedible offal’s (stomach and gastrointestinal tract) were recorded soon after slaughter and expressed as percentage of slaughter weight. Carcass yield was calculated as per the following formula.
 

  

 
Intestinal histomorphometry
 
The small intestine of one randomly chosen animal per replicate from the four groups was taken for histomorphometry examination. The ilium samples approximately 4-5 cm from the pylorus were carefully dissected (2 cm of tissue samples) during the slaughter time and were first rinsed with saline (0.85% NaCl) and preserved in 10% formalin solution. The routine histological methods were applied to the specimen and were trimmed and transverse sections of 4-5 micron were stained with hematoxylin and eosin. The slides were examined under x 10 magnification and micrographs were taken with trinocular light microscope (Labomed, L x 400. Labo America, Inc. USA) supplied with a computerized digital camera (IVU 3000). Images were analyzed to measure the crypt depth and villi height using stereological image software which its scale was calibrated to the micrometer unit (µm) using a micrometric ruler. The villus height was measured (3-5 villi per sample) from the villus tip to villus-crypt junction. Measurements for crypt depth were taken from the base of the villus to the submucosa were followed as per the procedure Helal et al., 2021.
 
Meat proximate composition
 
Meat samples were collected from the breast portion of carcasses per treatment, wrapped individually in polythene bags and immediately placed in a refrigerator (+4^oC) until used for chemical analysis. Collected meat samples were analyzed for moisture, fat, protein and ash content (AOAC, 2016).
 
Statistical analysis
 
Data generated from the trials were compiled and were analysed by one way analysis of variance (ANOVA) using SPSS software for window (Version 17.0, SPSS, Inc., Chicago, IL).

Carcass characteristics
 
Effect of feeding paragrass and probiotics combination on the carcass characteristics of grower Soviet Chinchilla rabbits is presented in Table 3. Highly significant increases  (P<0.01) were noticed in live weight (3.11±0.09 and 3.36±0.28 kg), slaughter weight (2.85±0.12 and 3.22±0.12 kg), after bleeding weight (2.64±0.12 and 2.87±0.16 kg), carcass with giblet weight (2.09±0.08 and 2.31±0.14 kg) and hot carcass weight (1.80±0.06 and 2.07±0.07 kg) of T₃ and T₄ groups respectively compare with T₁ and T₂. The hot carcass weight of the T₄ (2.07±0.07 kg) group was the highest, suggesting that a higher level of probiotics may further enhance carcass yield. Also, the weight of the head was found significantly higher in T₃ and T₄ group with no significant difference in yield among different groups. However, no significant difference was noticed in the dressing percentage of rabbit fed with different feeding regime. But relatively the yield of feet % was found higher in T₁ and T₂ when compare with T₃ and T₄.


       
However, improved live weight, slaughter weight, after bleeding weight, carcass with giblet weight and hot carcass weight, highlights the growth-promoting effects of probiotics in rabbits (García-Ruiz  et al., 2019; Riad et al., 2017) and improved carcass characteristics in rabbits fed with probiotics in T₄ group (Probiotics at 0.2%) when compared with T₁, T₂ and T₃. This might be due to increased nutrient utilization and improvement in gut health in rabbits, attributed to probiotics, likely contributing to these results (Bovera et al., 2010). Rabbit in all dietary groups had similar dressing yield (Ranges from 59.67 to 64.40%), which corroborate with earlier findings of Marounek et al., 2007; Rotolo et al., 2014 on effect of live yeast (Saccharomyces cerevisiae var. boulardii); diet supplemented with conjugated linoleic acid on the productive performance and meat quality of rabbit. Kouadio et al., 2023 reported that slaughter traits of rabbit were not affected by Sun-Dried Stylo hay as a dietary fiber source in rabbit.
 
Edible and inedible offals %
 
Effect of feeding para grass and probiotics combination on the offals % of grower Soviet Chinchilla rabbits were presented in Table 4. Heart (7.31±0.60 and 7.36±0.48 gm), liver weight (62.58±3.74 and 66.30±5.53 gm) and kidney weight (16.10±0.58 and 17.48±0.45) had a significant increase (P<0.05 and P<0.01) in T₃ and T₄ groups respectively compare with T₁ and T₂ groups. However, in the yield of kidney was significantly lower in the T₂ and T₃ groups compared to T₁, but not in T₄. However, the heart and liver percentage did not show significant variation across treatments. The present result was consistent with the findings of Abdel-Azeem  et al., 2018 and Hou et al., 2020 observed that addition of anaerobic probiotic on the diet of rabbit increased (P<0.05) the percentage of liver, with no significant effect on percentage of heart and kidney compare to control diet.

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Inedible offals, including stomach and whole intestine weights, as well as total inedible offals weight did not show significant differences (P>0.05) across the dietary treatments. It indicates that combined effect of paragrass and concentrate feed mixed with probiotics at 0.1 and 0.2% level did not substantially affect the nonedible organs of rabbit. Chandra et al., (2015) also reported similar non significant findings in the weight of inedible offals in rabbit ration supplemented with probiotics Kemzyme HF @ 0.05 % (Saccharomyces boulardi 50% and Pediococcus acidilactii 50%) and enzymes (cellulose, xylanase, pectinase, b- glucanase, amylase, protease and lipase).
 
Carcass measurements
 
Effect of feeding paragrass and probiotics combination on carcass measurements of grower Soviet chinchilla rabbits were presented in Table 5. Significant increase (P<0.01 and P<0.05) were noticed in carcass length (39.16±0.70 and 40.18±0.79 cm), thorax circumference (24.63±0.33 and 26.63±0.82 cm), thorax length (16.85±0.69 and 17.10±0.62 cm), hind leg length (20.11±0.84 and 20.56±0.99 cm), fore leg circumference (10.11±0.44 and 11.21±0.47 cm) and non-significant increase (P>0.05) was noticed in for leg length, loin length and lumbosacral length, of rabbit fed with probiotics (T₃ and T₄) compared to group receiving only paragrass and concentrate (T₁). This enhancement in carcass length can be attributed to the synergistic effects of paragrass and higher level of probiotics supplementation especially at 0.2% (T₄), which may promote better nutrient absorption and muscle growth. These findings corroborated with previous research studies, that demonstrated the positive impact of probiotics on growth performance and carcass characteristics of rabbits (Bovera et al., 2010).
 
Cut-up parts
 
Effect of feeding paragrass and probiotics combination on the cut-up parts % of grower Soviet Chinchilla rabbits were presented in Table 5. Significant increases (P<0.05)  in Thorax (381.33±14.89 gm), Shoulder (313.12±9.21 gm), Loin weight (365.80±14.5 gm), abdominal flap (143.43±6.65 gm) and Rump (158.98±6.21 gm) were highest in T₄ group (combination of paragrass and concentrate feed mixed with probiotics at 0.2%) followed by T₃, T₂ and T₁. Similar findings on carcass characteristics were reported by Memon et al., 2024 and Öztürk and Yıldırım (2005) respectively in rabbit fed with dietary prebiotic, probiotic and symbiotics.

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Intestinal villus morphology
 
Effect of feeding para grass and probiotics combination on the intestinal villus morphology of grower Soviet chinchilla rabbits were presented in Table 6. Combined effect of feeding paragrass and concentrate feed mixed with probiotics at 0.05, 0.1 and 0.2% showed significant variation and had a positive effect (P<0.01 and P<0.05) on the height and width of the villi in all three segments of small intestine such as duodenum (8492.33±296.99 and 730.83±24.37 µm), jejunum (6112.33±267.03 and 625.00±25.61 µm) and ileum (4846.33±84.10 and 584.50±36.33 µm) respectively in T₄ groups as compare with T₁, T₂ and T₃ groups. This description was also stated by William and Linda (2000). Villus height and the ratio of villus height to crypt depth are indicators of gastrointestinal tract morphology (Shamoto and Yamauchi, 2000) and intestinal histomorphology are one of the important indications of gut health in different animal species. The surface area of the intestinal villi plays an important role in the absorption of nutrients by small intestine. Moreover, the improvement of available nutrients in intestine would, result in increasing weights of visceral organs and improving growth performance of animal.

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Meat quality characteristics
 
Effect of feeding a combination of paragrass and probiotics on the meat quality of grower Soviet Chinchilla rabbits was assessed, as presented in Table 7. No significant differences (P>0.05) were noticed in moisture, protein, crude fiber, total ash, nitrogen free extract except fat %. Similar findings was also reported by Chandra et al., 2015, on dietary supplementation of probiotics and enzymes on meat composition of broiler rabbits. This research study shows that probiotics had significant effect on fat content, while other meat quality parameters, including moisture, crude protein, total ash and nitrogen-free extract.

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It was concluded from the above experiment that supplementation of probiotics @ 0.2% with paragrass and concentrate had beneficial effect in terms of carcass quality (i.e. live weight, hot carcass weight, carcass measure-ments, cut-up parts and specific organ weights etc.) and meat quality (i.e. ether extract, moisture, protein, ash content etc.) of growing Soviet Chinchilla rabbits. 

The authors are thankful to the Livestock Farm Complex, Madhavaram Milk Colony, Chennai-600 051 for providing necessary funds, laboratory facilities and manpower to conduct the research work.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish or preparation of the manuscript.