Impact of Four Fiber Sources and the Strategy of Feeding on the Nutritional Quality of Rabbit Meat (Oryctogalagus cuniculis) ()
1. Introduction
In Benin and in the West African sub-region, rabbit farming helps to strengthen food and nutritional security and contributes in part to the socio-economic development of the population [1] . The rabbit is a short-cycle species with a high prolificacy [2] . Its breeding is a source of employment and income for young and women [1] . Rabbit meat has a good profile in unsaturated fatty acids and proteins of high biological value, and has exceptional nutritional qualities. It is rich in minerals, trace elements (potassium, phosphorus, and selenium), and B vitamins [3] .
Despite these advantages, rabbit production is not able to adequately satisfy the high demand for rabbit meat. It is still subject to several factors that hinder its development [4] . Among these, rabbit feed is one of the factors to be controlled to reduce the cost of production and to make the products more accessible to the population. Rabbits are herbivores and have the ability to convert fodder into meat [5] . Therefore, several local plants and by-products have been used as fodder resources to improve the zootechnical performance of rabbits and reduce the cost of production. These include the leaves of Moringa oleifera, Cissus populnea, Synedrella nodiflora, Gliricidia sepium, Andropogon gayanus Aeschynomene histrix, Stylosanthès hamata and Arachis pintoïs and maize bran which have been used in rabbit feeds due to their protein, fiber content and accessibility [6] [7] [8] . These forages are incorporated into or supplemented with conventional feed and provide fiber, vitamins, and minerals [5] . However, these studies have not highlighted the influence of forage and agricultural by-products on the nutritional quality of meat, even though the nutrition of an animal affects the quality of its meat [9] . It is, therefore, necessary to assess not only the effect of local forage and by-products, but also to determine the influence of their distribution strategy on the nutritional quality of rabbit meat. Hence, the present work whose general objective is to improve the nutritional quality of rabbit meat in Benin uses the leaves of Gliricidia sepium, Leucaena leucocephala, Moringa oleifera and palm nut fibers.
2. Materials and Methods
2.1. Study Framework
The experimental study on rabbits was carried out with the technical support of the Laboratory of Poultry Science and Zoo-Economy (LaRAZE) and occurred from August to November 2020 on the application form of the Faculty of Agronomic Sciences of the University of Abomey-Calavi (FSA) located in the Commune of Abomey-Calavi. The Commune of Abomey-Calavi is located in the Atlantic department in the south of Benin and lies between 6˚21 and 6˚42 North and 2˚13 and 2˚25 East. The climate is sub-equatorial with four seasons: a long dry season (early December to March), a long rainy season (March to July), a short dry season (August to mid-September) and a short rainy season (mid-September to early December). The average annual rainfall is around 1200 mm, of which 700 to 800 mm is for the long rainy season and 400 to 500 mm for the short rainy season. As for the temperature, the maximums vary between 28˚C and 32˚C while the minimums vary between 24˚C and 27˚C. As for humidity, the minima vary from 55% (January) to 77% (June) and the maxima from 88% (March) to 95% (June) [10] .
2.2. Plant Material
Four sources of fiber, namely, Moringa oleifera leaves, Gliricidia sepium, Leucaena leucocephala, and palm nut fiber were used. Table 1 showed depending on the fiber source, four complete rations were made up of concentrates of different compositions for each fiber source.
2.3. Animal Material
The experiment involved 128 local rabbits of masculine sex and aged seven (07) weeks. The young rabbits were subjected to different fattening regimes for eight weeks.
2.4. Methodology
In the first step, 128 local rabbits were fed with feed and fiber sources. The leaves have been dried to ambient temperature before use. At the end of the fattening period, the rabbits were slaughtered and the carcasses were used to determine the nutritional quality. At the same time, the physico-chemical characteristics of the feed used to feed the rabbits were determined.
2.4.1. Experimental Design
The young rabbits were housed in wire mesh cages equipped with a drinking trough and a feeder. They were divided into four (4) batches of 32 rabbits. Each batch was then subdivided into two subgroups of 16 rabbits. Two subgroups of the same batch were fed, one with a complete feed (feed with incorporated fiber source) served all the day (at 9:00 am and 4:00 pm); and the other, with the same feed without incorporated fiber source, served only in the morning (at 9:00 am) and supplemented with the fiber source (identical to the one used to prepare the complete feed) served only in the evening (at 16:00). This constitutes two feeding strategies for each fiber source; a continuous feed and sequential feed. A total of four complete feeds were then served for continuous feeding and four types of feeds (feeds supplemented with fiber sources) were served sequentially.
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Table 1. Ingredients and nutritional composition of the four complete rations.
Complete feed Gliricidia sepium: CFG; Complete feed Leucaena leucocephala: CFL; Complete feed Moringa oleifera: CFM; Complete feed palm nut fiber: CFF.
The different rations served during the experiment for the eight (8) subgroups, were:
- complete feed Gliricidia sepium (CFG);
- supplemented feed Gliricidia sepium (SFG);
- complete feed Leucaena leucocephala (CFL);
- supplemented feed Leucaena leucocephala (SFL);
- complete feed Moringa oleifera (CFM);
- supplemented feed Moringa oleifera (SFM);
- complete feed palm nuts fiber (CFF);
- supplemented feed palm nut fiber (SFF).
2.4.2. Slaughter of Rabbits and Collection of Meat Samples
Four 15-week-old rabbits per feed treatment were selected according to the average weight of each batch for slaughter. The rabbits bled after being stunned by a sharp blow to the occipital region. The two-man dressing method described by [11] was used in this study.
2.4.3. Determination of the Physico-Chemical Composition of Feed and Meat
The physico-chemical composition of the rabbit feeds was determined through the levels of dry matter, ash, fat, and fiber. The Biceps femoris and Longissimus dorsi muscles from the different meat samples were dried at 65˚C for 72 hours. Subsequently, the contents of dry matter, ash, fat, and protein were determined according to standard procedures. The moisture content was determined in two replicates using the thermogravimetric method of the AOAC standard [12] . The determination of protein content was done according to the Kjeldhal method [13] . Lipids were determined by direct Soxhlet extraction and according to the AACC method [14] . The ash content was determined by the AACC method [14] . The crude fiber content of the feed was determined by the method of Weende [15] .
2.5. Statistical Analysis
Data was encoded using Microsoft Excel 2013 spreadsheet software. Means and standard deviations were calculated using SAS (Statistical Analysis System) software [16] . The effect of the fiber source and the influence of the feeding strategy on the nutritional characteristics of the feed and meat were evaluated. The generalized linear model procedure [16] was used for the analysis of variance. Fisher test was used to determine the significance of each effect in the model and the least squares means were estimated and compared while doing an analysis of variance (ANOVA with two factors), and then the comparison of the averages using Tukey Post hoc test.
3. Results and Discussion
3.1. Physico-Chemical Composition of Feeds
Table 2 shows that the dry matter contents for the complete feeds of dried leaves of Gliricidia sepium (CFG), of Leucaena leucocephala (CFL), of Moringa oleifera (CFM) and palm nut fiber (CFF) were similar (p > 0.05). The dry matter contents
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Table 2. Physico-chemical composition of rabbit feed.
CFG: Complete feed Gliricidia sepium; SFG: Supplemented feed Gliricidia sepium; CFL: Complete feed Leucaena leucocephala; SFL: Supplemented feed Leucaena leucocephala; CFM: Complete feed Moringa oleifera; SFM: Supplemented feed Moringa oleifera; CFF: Complete feed palm nut fiber; SFF: Supplemented feed palm nut fiber. NS: p > 0.05; *: p < 0.05; **: p < 0.01; ***: p < 0.001; mean in the same column followed by different letters differ significantly at the 5% threshold.
were 88.42%, 88.52%, 88.96%, and 89.42% for the Gliricidia sepium complete feed (CFG), palm nut fiber complete feed (CFF), Leucaena leucocephala complete feed (CFL) and Moringa oleifera complete feed (CFM) respectively. These dry matter values are close to those found (90.5% - 91.4%) on feeds made with 10% of M. oleifera leaves in Benin [17] . These values are also close to those found (87.08%) by [7] who incorporated 16.5% maize bran in the rabbit feed. The dry matter for feed without fiber sources such as feed supplemented in the evening with dried Gliricidia sepium leaves (SFG), feed supplemented in the evening with dried Leucaena leucocephala leaves (SFL), feed supplemented in the evening with dried Moringa oleifera leaves (SFM) and feed supplemented in the evening with the palm nuts fibers (SFF) was significantly influenced by the fiber source. Indeed, the dry matter content was high (p < 0.001) for the feed supplemented in the evening with dried leaves of Gliricidia sepium (SFG) (91.07%) compared to the feed supplemented in the evening with dried leaves of Leucaena leucocephala (SFL) (88.87%). The feed supplemented in the evening with dried Moringa oleifera leaves (SFM) and feed supplemented in the evening with palm nut fiber (SFF) had similar dry matter contents (p > 0.05) (90.03% and 90.08% respectively). For the different fiber sources, dried Leucaena leucocephala leaves (84.77%) had recorded low dry matter content (p < 0.001) compared to dried Gliricidia sepium leaves (86.53%) which gave similar dry matter content (p > 0.05) to that obtained for dried Moringa oleifera leaves and palm nut fibers (86.35% and 86.98% respectively). Moreover, the dry matter was similar to the dried leaves of Moringa oleifera and Leucaena leucocephala.
The ash levels of the whole feed, feed without fiber sources, and the different fiber sources themselves were similar (p > 0.05). These ash levels ranged from 8.41% to 10.30% (obtained by whole feed with palm nut fiber and palm nut fiber respectively). The ash levels obtained in this study are lower than those found in rabbit feeds containing 50% of Ipomoea batatas (14.24%) and Solanum melongena (14.05%) leaves [5] . These levels are rather close to those found by the same authors on rabbit feed containing 50% of Abelmoschus esculentus leaves (10.69%). Moreover, similar values of mineral contents (7.4% - 9.5%) were found in feeds containing Moringa oleifera leaves [16] .
Fat levels ranged from 7.15 (CFM) to 11.36% (CFF) for the complete feeds. The fat content recorded by the palm nut fiber-based complete feed (CFF) was higher (p < 0.001) than all other complete feeds. The fat levels were similar (p > 0.05) for whole feeds based on the dried leaves of Gliricidia sepium, Leucaena leucocephala (CFL) and Moringa oleifera (CFM). Feeds without fiber sources also had similar fat levels to whole foods made from the dried leaves of Gliricidia sepium, Leucaena leucocephala (CFL) and Moringa oleifera (CFM). These rates varied from 7.08 (SFM) to 8.32% (SFL). Regarding fiber sources, palm nut fiber obtained very high-fat contents (27.34%) (p < 0.001) compared to other fiber sources which gave similar fat contents (p > 0.05) (4.51%, 4.88% and 5.60% for dried leaves of Gliricidia sepium, Moringa oleifera, and Leucaena leucocephala respectively). This is due to the fact that palm nut fibers are residues from the oil extraction process. Therefore, the delipidation of palm nut fiber would be necessary for its efficient use in rabbit feed. In general, the fat percentages obtained for complete feed are high compared to the 3% to 5% margin recommended by Lebas [18] to cover the energy requirements of young rabbits.
The fiber contents were similar (p > 0.05) for all whole feeds. These fiber levels were 21.00%, 19.76%, 20.80%, and 19.37%, respectively, for the whole foods based on the dried leaves of Gliricidia sepium (CFG), Leucaena leucocephala (CFL), Moringa oleifera (CFM) and palm nut fiber (CFF). The fiber content of the feed without fiber sources ranged from 16.06% (SFF) to 20.50% (SFL). Feeds supplemented in the evening with the dried leaves of Gliricidia sepium (SFG), Leucaena leucocephala (SFL), and Moringa oleifera (SFM) also yielded similar fiber levels (p > 0.05). The fiber levels recorded by the feed supplemented in the evening with palm nut fiber (SFF) were also similar (p > 0.05) to those obtained by the feed supplemented in the evening with dried leaves of Gliricidia sepium (SFG) and the feed supplemented in the evening with dried leaves of Leucaena leucocephala (SFL). These fiber levels are close to those found in Nigeria (18.45% - 16.67%) on diets supplemented with some local plants (Bamboo, Senna, Gmelina) [19] . Palm nut fiber and dried Leucaena leucocephala leaves recorded high fiber levels (29.64% and 27.89% respectively) (p < 0.001) followed by dried Moringa oleifera leaves (23.85%) and dried Gliricidia sepium leaves (17.69%). These variations in the fiber composition of the various fiber sources are considered in the formulation of the different whole feeds such that their fiber compositions were the same.
3.2. Effect of Fiber Source and Distribution Method on the Nutritional Quality of Rabbit Meat
The nutritional parameters (dry matter, mineral content, fat, and protein) of the saddle and thigh of rabbits fed a continuous and sequential distribution of Gliricidia sepium (CFG), Leucaena leucocephala (CFL), Moringa oleifera (CFM) and palm nut fiber (CFF) sources are presented in Table 3.
3.2.1. Dry Matter Content
Across feeding strategies for the same fiber source, both in saddle and thigh muscle, no significant difference (p > 0.05) was found for the dry matter content of rabbits fed Leucaena leucocephala leaves or palm nut fibers. The dry matter content of the meat of rabbits fed the Gliricidia sepium complete feed was higher (p < 0.05) compared to that of rabbits fed the feed supplemented in the evening with Gliricidia sepium leaves. For the Moringa oleifera fiber source, the dry matter of the thigh was higher (p < 0.05) in favor of the rabbits fed the supplemented feed. However, the saddles of the same subjects had recorded similar dry
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Table 3. Nutritional composition of rabbit meat according to fiber source and strategy of feeding.
NS: p > 0.05; *: p < 0.05; **: p < 0.01; ***: p < 0.001; mean in the same column followed by different letters differ significantly at the 5% threshold.
matter levels (p > 0.05). Therefore the supply of dried leaves of Gliricidia sepium or Moringa oleifera in the evening would have had an impact on the overall nutrient content of the rabbits’ meat. This was not the case for fiber sources based on Leucaena leucocephala leaves or palm nut fibers, whose dry matter content remained unchanged regardless of the distribution method.
From one fiber source to another, at the saddle, the highest dry matter content (p < 0.05) was recorded by continuously distributed Gliricidia sepium (28.65%) compared to all other fiber sources which recorded similar content (p > 0.05). In the thigh, the lowest (p < 0.05) dry matter content (23.12%) was obtained by Moringa oleifera and the highest (p < 0.05) by the same fiber source distributed sequentially (27.33%). Thigh dry matter rates were equal (p > 0.05) for sequentially distributed Moringa oleifera, continuously distributed Gliricidia sepium and Leucaena leucocephala and for both sequentially and continuously distributed palm nut fibers. Similarly, the thigh dry matter rates recorded by the continuously distributed Moringa oleifera fiber sources were similar (p > 0.05) to those obtained by the sequentially distributed palm nuts and Gliricidia sepium fibers and continuously and sequentially distributed Leucaena leucocephala. These similarities observed between the dry matter contents of meat from different feed treatments show that the amount of nutrients in rabbit meat is not affected by the different fiber sources used. Thus, different fiber sources can be used as substitutes in rabbit feed without changing the overall nutrient content of the meat. The dry matter contents recorded in this study are close to those obtained by [20] (25% - 27.5%), and [21] (24.5% - 25.3%) on 15 - 18 weeks old rabbits fed commercial diets. These results are also similar to those of [8] (24.96% - 27.30%) on rabbits fed rations containing 30% of C. populnea or S. nodiflora leaves.
3.2.2. Ash Content
The mineral fraction of rabbit meat varied significantly (p < 0.05) at the saddle level for the Gliricidia sepium fiber source in favor of the continuous strategy and for Moringa oleifera in favor of the sequential strategy (p < 0.001). For Leucaena leucocephala and palm nut fiber sources, no significant difference (p> 0.05) in the ash content of the shavings was found between the distribution strategies. At the thigh level, there was no variation (p > 0.05) in ash levels between distribution strategies for Moringa oleifera and Leucaena leucocephala fiber sources. However, a significant difference (p < 0.05) was found for Gliricidia sepium and palm nut fiber sources in favor of continuous feeding. For rabbits fed Leucaena leucocephala leaves, ash levels were not affected by the mode of distribution regardless of muscle. Thus, the mineral fraction of the meat of the rabbits was not affected by the feeding method of Leucaena leucocephala leaves. Only the supply of dried leaves of Gliricidia sepium in the evening would have affected the mineral content of the rabbit meat. This is not clearly established for palm nut fibers and Moringa oleifera leaves.
Across fiber sources, ash levels were high (p < 0.001) in the saddles (3.49%) and thighs (3.56%) of rabbits fed the Gliricidia sepium leaf-based complete feed. The saddles of the rabbits fed the continuous palm nut fiber had the lowest (p < 0.001) ash values (0.91%), which were equal to those of the continuously fed Gliricidia sepium and Moringa oleifera fiber sources. In the thigh, low levels (p < 0.05) of minerals were recorded in sequentially distributed Gliricidia sepium (1.10%), which were similar to sequentially distributed palm nut fibers and both continuously and sequentially distributed Leucaena leucocephala and Moringa oleifera fiber sources. This shows that the substitution of these different fiber sources in the rabbit diet will not have a margining effect on the mineral fraction of the meat. Thus, the different fiber sources can also be substituted for each other in the sequential feeding of rabbits without changing the mineral content of the meat. The mineral levels found in this study are high compared to those obtained (1.03% - 1.23%) in rabbits fed rations containing 30% of C. populnea or S. nodiflora leaves [8] . These differences could be explained by the diet, in this case, the presence of different kinds of forage. Indeed, Combes [22] mentioned that it is very likely that feeding through supplementation is the main factor of variation in the mineral fraction of meat.
3.2.3. Fat Content
Across feeding strategies and for the same fiber source, no significant difference (p > 0.05) was observed for the fat content of rabbits fed Leucaena leucocephala and Moringa oleifera leaves. However, in general, fat was low when the rabbits were fed the fiber source in the evening. This difference was highly significant for rabbits fed G. sepium leaves and palm nut fibers. Fat levels were indeed high in the saddles (p < 0.05) and thighs (p < 0.001) of the rabbits fed the G. sepium leaf-based complete feed. For rabbits fed palm nut fiber, it was in the thigh that the lipid content was high (p < 0.001) in favor of continuous distribution. Thus, the distribution mode of Leucaena leucocephala and Moringa oleifera leaves did not affect the quality of the rabbits’ meat, in this case, its fat content. On the other hand, feeding rabbit with G. sepium leaves or with palm nut fibers on a continuous feeling basis increased the fat content of the meat. However, this effect on meat quality seems to be attenuated when the fiber is used in the evening.
Thigh meat from rabbits fed palm nut fiber had the highest fat levels (p < 0.001) in continuous and sequential distribution (5.12% and 4.18% respectively). At the saddle level, the fat levels of these same subjects were also high (p < 0.05) and similar (p > 0.05) to those recorded by G. sepium and M. oleifera in a continuous distribution, which is similar (p > 0.05) to all other fiber sources. The fat levels obtained in this study for thighs are high compared to the margin of 2.90% - 3.22%, obtained on labeled rabbits [23] . The high-fat content of meat from rabbits that were fed palm nut fiber as a source of fiber may be explained by the fat content of the palm nut fiber itself. Palm nut fibers, which are residues of palm oil extraction, give the feed a high-fat content, which relatively increases the fat content in the thigh meat. Therefore, the use of low-fat extraction residues will allow the production of rabbit meat with lower fat content. Indeed, Combes [22] mentioned that diet is one of the most important factors influencing the amount of lipid fraction in rabbit meat. Thus, to substitute palm nut fiber for other sources of fiber in rabbit diets, residues with low fat levels should be used.
3.2.4. Protein Content
The distribution strategy of the different fiber sources had no influence (p > 0.05) on the protein contents of the rabbits in both the thigh and the saddle. Therefore, these different fiber sources can be used continuously or sequentially without affecting the protein content of the rabbit meat.
From one fiber source to another, the highest protein contents in the saddle were obtained by the fiber source of G. sepium (22.56% and 20.91% in continuous and sequential distribution, respectively). For the other fiber sources, the protein contents were equal (p > 0.05). Protein contents were also similar (p > 0.05) for the shreds in sequential distribution. In the thigh, palm nut fiber gave the highest protein contents (24.46% and 23.05%) (p < 0.05) and similar (p > 0.05) to the G. sepium fiber sources which in turn were equal to all other fiber sources. The protein levels found were close to those obtained for rabbits at commercial slaughter ages and weight (19.5% - 22.5%) [22] . The similarities in protein content show that these different fiber sources can be substituted in the rabbit diet without changing the protein content of the meat. Moreover, the protein levels in the rabbits’ thighs were higher than in the saddle. This is in line with Combes [22] who reported that among the cuts, the edible part of the leg is the richest in protein.
4. Conclusions
This study showed the influence of four sources of fibers and the strategy of feeding on the nutritional quality of rabbit meat. Complete feed of palm nut fibers, or of Gliricidia sepium, or of Leucaena leucocephala or of Moringa oleifera have been tested facing the supplemented feed of the same fiber sources. To ensure good nutritional quality of rabbit meat, Leucaena leucocephala, Moringa oleifera, Gliricidia sepium leaves, and palm nut fiber can be substituted as a source of fiber in rabbit feed. However, a delipidation of palm nut fibers is necessary for its use in rabbit feed. Regarding the mode of distribution, the sequential feeding method can be recommended in rabbit farming for the efficient use of palm nut fibers or G. sepium leaves.
It would be interesting to continue this work by determining the influence of the chemical composition of the leaves of Leucaena leucocephala, Gliricidia sepium, and Moringa oleifera on meat quality.
Acknowledgements
The authors are grateful to the Program Competitive Funds of Research Phase III (PFCR3/CS/UAC) of the University of Abomey-Calavi, Benin, through the Feed Supplements for Animals project (CAPA).