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The use of forage plants for feeding rabbits, offered in a complementary way in diets, represents a viable option to produce animal protein. The potential of these tropical plants is determined by their nutritional composition and availability (Mireles et al. 2017). Balanced diets associated with forages satisfy the nutritional needs of rabbits and, consequently, favor the productive performance of the animal (Osmari et al. 2019). In recent years, important studies have been carried out on the use of Moringa oleifera in rabbit production (Valdivié et al. 2019).
Food evaluation allows knowing its nutritional potential and its possible effect on its nutritional use by animals (Al-Sagheer et al. 2019). There are several methodologies described for this purpose (Ferreira et al. 2019). Among them, digestibility tests are an efficient technique to evaluate the digestive utilization of rabbit diets and the functioning of their digestive tract (López et al. 2018).
The objective of this experiment was to determine in vivo digestibility of nutrients of moringa forage meal in rabbit diets.
Materials and Methods
Preparation of forage meal. The tree species Moringa oleifera cv. Brazilian, established at the Estación Experimental de Pequeños Animales de Carpina, from the Universidad Federal Rural de Pernambuco. Moringa forage meal was made from leaves, petioles and fine stems, collected at 60 d of age. The cut was manually performed, at a height of 50 cm. Drying of plant material was carried out for five days in a warehouse, protected from sun and rain. To ensure it dries evenly, and to avoid the development of fermentation processes, it was turned over three times a day. Finally, the plant material was reduced to a particle size of 3 mm in a hammer mill. Moringa forage meal was packed in 50 kg jute bags. It was kept indoors and aerated until its use. Six representative samples, 500 g each, were taken from a single batch of forage meal. Samples corresponded to five areas of the bags (upper and lower corners and center). They were stored in glass jars and stored at room temperature for 10 d. Analyzes were carried out by triplicate. Table 1 shows the chemical and energy composition of moringa forage meal.
Table 1 Chemical and energy composition of moringa forage meal
| DM, g/kg | CP, g/kg DM | GE, kcal/kg | NDF, g/kg DM | ADF, g/kg DM | |
|---|---|---|---|---|---|
| n=12 | 880.80 | 185.40 | 4395.44 | 435.00 | 272.60 |
GE: gross energy
Experimental animals and diets. Digestibility test was carried out in the Laboratorio de Digestibilidad de No Rumiantes, from the Departamento de Zootecnia de la Universidad Federal Rural de Pernambuco. Thirty-two White New Zealand rabbits (males) aged 55 d, housed in metabolic cages, were used. Animals were randomly distributed into four experimental groups. Control diet was formulated according to the nutritional needs established by de Blas and Mateos (2010), and the treatments replaced 100, 200 and 300 g/kg of the macro ingredients (food except the nucleus) by moringa forage meal (table 2). The core was composed of molasses, common salt, premix, DL-methionine, L-lysine and bentonite. Diets were supplied in the form of granules, with dimensions of 8.0 mm long and 4.0 mm diameter.
Table 2 Ingredients and analyzed chemical composition (g/kg) of experimental diets containing different levels of moringa forage meal
| Ingredients, g/kg | Moringa forage meal, g/kg | |||
|---|---|---|---|---|
| 0 | 100 | 200 | 300 | |
| Alfalfa meal | 400.00 | 358.50 | 316.90 | 275.40 |
| Wheat meal | 50.00 | 44.80 | 39.60 | 34.40 |
| MDPM1 | 150.00 | 134.40 | 118.80 | 103.30 |
| Soy bean meal | 137.00 | 122.70 | 108.40 | 94.10 |
| Moringa forage meal | - | 100.00 | 200.00 | 300.00 |
| Corn meal | 117.10 | 105.00 | 92.90 | 80.70 |
| Soy bean oil | 73.90 | 66.20 | 58.60 | 50.90 |
| Sugar cane molasses | 30.00 | 26.90 | 23.80 | 20.70 |
| Sodium chloride | 20.00 | 20.00 | 20.00 | 20.00 |
| Mineral-vitamin premix2 | 5.00 | 5.00 | 5.00 | 5.00 |
| Calcium carbonate | 5.00 | 5.00 | 5.00 | 5.00 |
| Bicalcium phosphate | 4.90 | 4.40 | 3.90 | 3.40 |
| Bentonite | 5.00 | 5.00 | 5.00 | 5.00 |
| L-Lysin | 1.10 | 1.10 | 1.10 | 1.10 |
| DL-Methionine | 1.00 | 1.00 | 1.00 | 1.00 |
| DM | 907.60 | 900.00 | 890.30 | 887.30 |
| CP | 201.20 | 188.50 | 176.50 | 168.50 |
| DE. kcal/kg | 2489 | 2403 | 2317 | 2230 |
| NDF | 272.60 | 337.30 | 348.70 | 353.90 |
| ADF | 222.40 | 257.30 | 282.20 | 278.40 |
1MDPM: Shredded corn with straw and corncob
2Composition of premix per kg of product: vit. A, 2´000,000 IU; vit. D3, 20,000 IU; vit. E, 4,000 mg; vit. K3, 722 mg; vit. B1, 400 mg; vit. B2, 1000 mg; vit. B6, 600 mg; vit. B12, 2,000 mcg; niacin, 6,000 mg; folic acid, 100 mg; pantothenic acid, 3,000 mg; biotin, 21 mg; choline, 100,000 mg; selenium, 19 mg; iodine, 140 mg; cobalt, 200 mg; iron, 20,000 mg; copper, 4,000 mg; manganese, 4,000 mg, zinc, 14,000 mg.
Experimental procedure. Animals adapted to diets and cages for seven days. Excretions were collected for four consecutive days, according to the methodology proposed by Pérez et al. (1995a). Food and water intake was ad libitum. During the experimental period, the natural photoperiod was maintained. Maximum average temperature of the environment was 27.0 °C and relative humidity of the air was 70.1.
Excretions were kept frozen at -20 °C until the moment of their analysis. Subsequently, they were dried in the oven at 55 °C for 72 h. Finally, they were ground in a mill to reduce the particle size to 1 mm.
Diets and feces were analyzed to determine dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF), according to the methodology described by Silva and Queiroz (2009). Gross energy (GE) determination was performed on an adiabatic pump calorimeter (model 6200, Parr Instrument Company, Moline, Illinois, USA).
The apparent fecal digestibility of nutrients was determined according to the equation suggested by Pérez et al. (1995b):
Digestible energy (DE) of diets was obtained by multiplying GE digestibility value by the gross energy value, obtained from each diet. The same calculation was made for digestible protein (DP) of diets.
The relationship (REL) between DE and DP was determined by the following formula:
Nutritional value of ingredients and their relation was calculated according to Ferreira (2014).
Experimental design and statistical analysis. An analysis of variance was carried out, according to a completely randomized design with four treatments and eight repetitions. Duncan (1955) test was applied for the mean comparison for P <0.05. Results were processed using the R program (R Core Team 2017).
Results and Discussion
Table 3 describes the apparent fecal digestibility of nutrients in rabbits fed diets containing increasing levels of moringa forage meal.
Table 3 Apparent fecal digestibility of nutrients in rabbits fed increasing levels of moringa forage meal
| Moringa forage meal , g/kg diet | SE ± | P | ||||
|---|---|---|---|---|---|---|
| 0 | 100 | 200 | 300 | |||
| Intake, g DM | 127.64a | 117.78ab | 109.66ab | 97.76b | 6.81 | 0.0296 |
| Excretion, g DM | 45.76 | 43.09 | 41.11 | 39.34 | 3.30 | 0.5614 |
| DM | 63.99 | 63.53 | 62.58 | 60.20 | 1.51 | 0.3110 |
| OM | 64.37 | 62.57 | 62.61 | 60.29 | 1.52 | 0.3334 |
| CP | 79.14 | 74.42 | 75.59 | 75.78 | 1.44 | 0.1389 |
| GE | 66.65 | 64.63 | 63.07 | 60.91 | 1.49 | 0.0680 |
| NDF | 48.72 | 51.07 | 51.27 | 48.00 | 2.16 | 0.6304 |
| ADF | 39.20 | 40.93 | 42.56 | 41.88 | 2.77 | 0.8425 |
abMeans with different letters in the same line indicate significant differences P<0.05
Differences were observed with respect to control group in food intake in rabbits that ingested diets with moringa forage meal. These results are similar to the high content of indigestible fiber present in diets with moringa forage meal (table 2). Lara et al. (2012) explained that food intake is influenced by the level and type of fiber in the diet. Blas et al. (1999) reported that the retention time of digesta in the cecum could increase when there is a high supply of less digestible fiber in the diet, and concomitantly it can decrease food intake. Gidenne (2000) stated that when acid detergent fiber content is higher than or equal to 250 g/kg DM, animals do not consume enough food to meet their energy needs.
Pinheiro et al. (2018) suggested other factors, such as physical properties of cell wall components that influence on intake. The high volume (6.92 mL/g) of moringa forage meal could cause a state of physical satiety for a long time in the animal and, consequently, a reduction of the stimulus to consume food until the transit speed of digesta was reduced. (García 2006). Adeniji and Lawal (2012) observed a similar trend with the substitution of peanut (Arachis pintoi) cake meal for different levels of moringa foliage flour (0, 100, 200, 400, 600 and 800 g/kg).
Apparent fecal digestibility of nutrients in rabbits did not show significant differences among treatments. This could be due to the effect of accumulation of ingest in the cecum, caused by the level and characteristics of fibrous fractions present in diets. A longer retention time of digesta in this digestive segment stimulates the increase of fermentative activity (García et al. 1999). According to Gidenne et al. (2000), by increasing fiber in the diet of rabbits, its digestibility is improved by an increase of quantity and quality of cecal microbiological activity, because, in this type of forage with low maturity degree, residues of esterified xyloses with acetyl groups are not present. These esters prevent fiber degradation in forages with higher maturity level due to a limitation of specificity of microbial enzymes by polysaccharides.
It is important to highlight that values of apparent fecal digestibility of CP, GE, DM and OM were above 60%. Abu Hafsa et al. (2016) reported lower rates of apparent fecal digestibility (except for the ADF and GE) with the inclusion of 150 g/kg of three tree foliage (Acacia saligna, Leucaena leucocephala and Moringa oleifera) in diets for rabbits. In contrast, Caro et al. (2018) indicated superior values with the inclusion of moringa cv. supergenius (0, 150 and 300 g/kg) in diets for rabbits.
Studies carried out with other forage sources showed inferior values with the inclusion of 300 g/kg of foliage of mulberry, leucaena, naranjillo and forage peanuts (M. alba, L. leucocephala, Trichanthera gigantea and A. pintoi, respectively) in granulated diets for fattening rabbits (Nieves et al. 2011). Variations in the results are due to factors related to fibrous material used (genotype, phenological state, frequency and age of cut, drying method, presentation method and some others), and other factors inherent to the animal.
Digestible energy content in rabbits did not differ among treatments (table 4). In contrast, digestible protein decreased (P<0.001) in the animals that consumed the diets with moringa forage flour. The group that ingested the diet with 300 g/kg of moringa forage meal increased the DP contribution by 16.2 and 14.25 g/kg DM with respect to the treatments with 100 and 200 g/kg of moringa forage meal in the diet. This effect was determined by the reduction of crude protein content in diets with moringa forage meal (100 and 200 g/kg, respectively). Villamide et al. (2010) stated that the nutritional value of a protein is determined not only by its amino acid composition, but also by its digestibility or proportion of ingested protein that is digested in the intestine. However, values obtained are higher than DP requirements proposed by Xiccato and Trocino (2010) for this animal category (105-110 g/kg DM).
Table 4 Content of digestible nutrients in diets with different inclusion levels of moringa forage meal
| Moringa forage meal, g/kg diet | SE ± | P-value | ||||
|---|---|---|---|---|---|---|
| 0 | 100 | 200 | 300 | |||
| DE1, kcal/kg DM | 3024.14 | 2874.06 | 2847.75 | 2785.00 | 67.32 | 0.1024 |
| DP2, g/kg DM | 172.45a | 122.71c | 124.66c | 138.91b | 2.59 | < 0.001 |
| DE:DP3, kcal/g | 17.55c | 23.43a | 22.84a | 20.05b | 0.35 | < 0.001 |
abcMeans with different letters in the same line indicate significant differences for P<0.05
1Digestible energy
2Digestible protein
3Relation digestible energy: digestible protein
There is little research reporting on the content of digestible nutrients from alternative fiber sources used in rabbit feeding. Nieves (2009) reported 2,322 kcal/kg DM of DE and 139 g/kg DM of DP for diets containing 300 g/kg of mulberry foliage. Meanwhile, in diets with tithonia (Tithonia diversifolia) foliage, digestible energy and protein values were 2,139 kcal/kg and 109 g/kg, respectively (Nieves et al. 2011). The evident variability can be attributed to the experimental procedure (determination method, inclusion levels of plant material, age of animals and laboratory measurements) and to the chemical composition of studied forage material, among other possible causes. Raharjo (1987) established a range for DE, which varies between 2,179-2,903 kcal/kg DM, in diets for rabbits fed tropical forages.
The relationship between the content of digestible energy and digestible protein determines that fiber level is a fundamental variable in rabbit diets (Hernández and Dalle Zotte 2010). This proportion increased (P <0.001) in rabbits fed diets containing moringa forage meal, being lower in the group that consumed the diet with 300 g/kg. Gidenne et al. (2017) concluded that when energy concentration of the diet is between 2,151-2,987 kcal/kg DM, the rabbit maintains constant intake of DE. According to de Blas et al. (1988), a ratio of 23 kcal DE/g DP is required to maintain the growth rate (23 g/day). Values of energy-protein ratio superior to 25 kcal DE/g DP) are associated with increased mortality in rabbits due to post-weaning diarrhea (de Blas et al. 1986). Lebas et al. (1996) proposed that the proportion should range between 22.5-24.9 kcal DE/g DP during the growth-fattening period.
Results demonstrated the nutritional potential of moringa forage meal, when it is used up to 30% in rabbit feeding.
