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- Nutritive value of Adenodolichos rhomboideus leaves compared with Leucaena leucocephala and Stylosanthes guianensis forages in indigenous goats in Lubumbashi (DR Congo)
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Nutritive value of Adenodolichos rhomboideus leaves compared with Leucaena leucocephala and Stylosanthes guianensis forages in indigenous goats in Lubumbashi (DR Congo)
Notes de la rédaction
Received on May 2, 2013; accepted on April 7, 2014
Résumé
Valeur nutritive des feuilles de Adenodolichos rhomboideus en comparaison de fourrages de Leucaena leucocephala et de Stylosanthes guianensis chez la chèvre locale à Lubumbashi (R.D. Congo). Les fourrages de trois espèces végétales (Adenodolichos rhomboideus, Leucaena leucocephala, Stylosanthes guianensis) ont été évalués des points de vue de leur composition chimique, consommation volontaire et digestibilité apparente de la matière sèche (MS), de la matière organique (MO), de la protéine brute (PB), des fibres insolubles dans le détergent neutre (NDF) et des fibres insolubles dans le détergent acide (ADF) utilisant à cette fin six chèvres mâles (17,1 kg ± 0,7) dans un dispositif en double carré latin 3 × 3. Le fourrage de S. guianensis a présenté une faible teneur en PB (p < 0,001) par rapport aux feuilles de A. rhomboideus et au fourrage de L. leucocephala. Les teneurs en fibres (ADF et NDF) ont été plus faibles (p < 0,001) dans le fourrage de L. leucocephala que dans les feuilles de A. rhomboideus et le fourrage de S. guianensis. Le fourrage de L. leucocephala a montré les teneurs les plus élevées en PB, matières minérales et extraits éthérés. La digestibilité apparente et la consommation volontaire de PB ont été les plus élevées pour L. leucocephala et les plus faibles pour les feuilles de A. rhomboideus (p < 0,05). La teneur en protéines digestibles a été similaire pour les trois fourrages. Leucaena leucocephala semble être le mieux adapté pour la production carpine. Les faibles digestibilités et consommations de feuilles de A. rhomboideus peuvent être dues aux effets négatifs de certains facteurs anti-nutritionnels comme les tanins.
Abstract
Three forages (Adenodolichos rhomboideus, Leucaena leucocephala, and Stylosanthes guianensis) were evaluated for their chemical composition, and for both voluntary intake and apparent in vivo digestibility of dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), and acid detergent fibre (ADF) as estimated by six goats (17.1 kg ± 0.7) used in a 3 × 3 double Latin square design. Forage from S. guianensis had a lower (p < 0.001) CP content than L. leucocephala forage and A. rhomboideus leaves. Fibre content (ADF and NDF) was lower (p < 0.001) in L. leucocephala (35%) forage than in A. rhomboideus (59.5%) and S. guianensis forages (56.5%). Leucaena leucocephala forage presented higher CP, ash, and ether extract levels, and higher digestibility and voluntary intake of CP. Adenodolichos rhomboideus leaves had lower (p < 0.05) apparent digestibility and intake of DM. Digestible CP content was similar for A. rhomboideus leaves and S. guianensis forage. Leucaena leucocephala appears to be the most adequate forage for goat production. Low digestibility and voluntary intake of A. rhomboideus leaves may be due to negative effect of an anti-nutritional factor such as tannin.
Table des matières
1. Introduction
1Ruminant livestock in the southeastern region of DR Congo, especially the indigenous goats that are those productive, suffer from inadequate nutrition during the dry season. This situation is caused by the scarcity of natural vegetation, primary source of forage, owing to lengthiness of the dry season, which lasts for more than six months and during which straw is mainly available. However, during this period, some species retain their green leaves and are available as fodder for ruminants. Among these feed sources are Adenodolichos rhomboideus, Leucaena leucocephala, and Stylosanthes guianensis.
2Adenodolichos rhomboideus is a herbaceous legume that is well adapted to local ecosystems and widespread in the region, growing on normal and soil contaminated by trace metal (Meerts, 2008). Its nutritional value for ruminants has never been investigated. Leucaena leucocephala is a shrub with high nutritional value and leaf availability is limited by tree height during the dry season. Garcia et al. (1996) reported that digestive energy and total apparent digested crude protein (CP) value for L. leucocephala ranged from 11.6 to 12.9 MJ·kg-1 and 64.7 to 78.0%, respectively. Rumen degradable protein (RDP) was found to be close to 42%, and undegradable protein (UDP) 48%, giving a TADCP value of 70%. Stylosanthes guianensis is a herbaceous legume having good nutritional value but its use in the dry season is limited by lignification. The metabolisable energy (ME), CP, and DMD values of S. guianensis forage have been reported to be close to 5.4 MJ·kg-1, 13.3 to 18%, and 52%, respectively (Ajayi et al., 2008). Several digestibility methods are used to assess the digestible value of forage, but in vitro and in sacco methods may lead to some erroneous conclusions if not supported by feeding trials (Norton, 1998). The form in which the leaves are offered (fresh, wilted, or dry) is also known to affect both intake and digestibility in some species (Palmer et al., 1992). Since there are no known techniques to predict palatability and intake, the nutritive value of forage species can only be accurately determined by feeding trials that give information on animal health and productivity. The aim of this study was to assess the nutrient content, intake, and digestibility of A. rhomboideus forage compared with L. leucocephala and S. guianensis fed to indigenous goats.
2. Materials and methods
2.1. Diets, animals, and experimental design
3Three different forages were tested from 15 June to 18 August 2010. These comprised A. rhomboideus leaves (Fabaceae), L. leucocephala (Mimosaceae), and S. guianensis (Fabaceae) forages. One to two months of regrowth of A. rhomboideus leaves were harvested at area golf Meteorology of Lubumbashi (DR Congo), 11°37’58.2” latitude south, 27°24’54.5’’ longitude east, 1,266 m altitude. Leucaena leucocephala was harvested from old trees (over 10 years old) at the University of Lubumbashi in the Faculty of Agriculture (Agronomic Faculty), 11°36’38” latitude south, 27°28’29.6’’ longitude east, 1,296 m altitude. Stylosanthes guianensis forage was obtained from experimental fields, established in December 2009 at the farm of the Faculty of Veterinary Medicine, University of Lubumbashi, 11°42’46.2” latitude south, 27°32’31.2’’ longitude east, 1,216 m altitude.
4These three forages were offered green. Forage from each species was harvested daily and mixed thoroughly before being offered to the goats as the only feed.
5Adenodolichos rhomboideus and L. leucocephala samples were collected as leaves with petiole, while S. guianensis was mown at 15 cm height approximately. To facilitate chewing, S. guianensis forage was chopped and A. rhomboideus and L. leucocephala were sorted to remove hard petioles and dry leaves before distribution.
6Six local yearling male goats, mean live weight 17.1 kg ± 0.73, were used. The animals were separated in two Latin squares of three animals each. Diets were offered twice daily over three periods of 21 days each, comprising 15 days of adaptation, followed by 7 days of data collection. Each group of animals was subjected to each forage according to the period.
7Voluntary intake and in vivo apparent digestibility of the forages were studied. Voluntary intake was determined by the difference between the quantity offered and refusal. In vivo apparent digestibility was determined by complete collection (Jetana et al., 2010) in pens measuring 120 cm × 80 cm × 70 cm.
8Water and trace mineral blocks were provided throughout the experimental period. The animals were weighed with a balance for maximum load and 0.1 kg accuracy on the initial day of the experimental period. Individual daily feed intake and total fecal production were also measured. The bulked fecal output from each animal was immediately weighed, mixed thoroughly, and sub-sampled for analyses. One sample of the offered forages was taken every day, dried in a forced air oven at 60 °C during 72 h, and ground through a 1-mm screen in an IKA WERKE type M20 machine.
9Ashes of forage and feces were determined with a muffle furnace at 560 °C for one night. Dry matter (DM) of forage and feces was determined by drying in an oven at 105 °C for 24 h. Protein content of forage and feces was determined with a Hach Digesdahl® Digestion Apparatus (Ref. No 23130-21) using the method described by Brayton (1992). Cell walls of forage and feces constituents (neutral detergent fibre [NDF] and acid detergent fibre [ADF]) were determined based on the Gerhardt FibreBag method established by Van Soest et al. (1991). Ether extract (EE) of forage and feces was determined by the Soxtec system method (Matsler et al., 2005).
2.2. Data analyses
10Data were analyzed using the general linear model (GLM) procedure of SAS (Statistical Analysis System Institute, 2010). Significant differences between feeds means were tested by using the ANOVA procedure and the Student’s t-test. The model for analysis included the effects of the forage, period, square, and animal. The effects due to periods, square, and animal were not significant.
3. Results
11The chemical composition of the forages is presented in table 1. Leucaena leucocephala was richer in CP, EE, and ashes than A. rhomboideus and S. guianensis. Forage from S. guianensis had a higher value for DM content, while A. rhomboideus had higher concentrations of OM, ADF, and NDF than the other forages.
All variables differed (p < 0.01) among the three forages in terms of intake (Table 2). 
12Voluntary intake of L. leucocephala and S. guianensis was higher than that of A. rhomboideus for organic matter (OM), DM, and EE (p < 0.01). Leucaena leucocephala had higher voluntary intake than S. guianensis and A. rhomboideus for CP (p < 0.001). NDF and ADF intake were higher for S. guianensis than L. leucocephala and A. rhomboideus (p < 0.01).
13Apparent digestibility coefficients of the different forages are presented in table 3.
14Stylosanthes guianensis and L. leucocephala had higher OM, DM, and CP digestibility than A. rhomboideus (p < 0.001). Leucaena leucocephala and A. rhomboideus had lower apparent digestibility coefficients of ADF (p < 0.001), NDF (p < 0.001), and EE (p < 0.05) than S. guianensis.
15Daily digestible intake of A. rhomboideus, L. leucocephala, and S. guianensis forages are given in table 4. Leucaena leucocephala and S. guianensis forages had higher (p < 0.01) digestible intake than A. rhomboideus forage for OM and DM. Forage from L. leucocephala had higher (p < 0.001) digestible intake of CP than A. rhomboideus and S. guianensis. Forage of S. guianensis had higher (p < 0.001) digestible intake of ADF and NDF than L. leucocephala and A. rhomboideus. Ether extract digestible intake was highest (p < 0.001) for L. leucocephala, followed by S. guianensis and then A. rhomboideus.
16Digestible nutrient content (g·kg-1 DM) of A. rhomboideus, L. leucocephala, and S. guianensis forages for indigenous goats are given in table 5. Leucaena leucocephala forage had higher (p < 0.01) digestible CP and EE contents than A. rhomboideus and S. guianensis. Leucaena leucocephala and A. rhomboideus forages had higher (p < 0.01) digestible OM and ashes contents than S. guianensis.
4. Discussion
17Dry matter of green forage classically varies between 12 to 50% fresh matter (Martin-Rosset, 1990; Djago et al., 2007). The DM content for all three forages in this experiment was high and linked to the fact that the study was conducted in dry season. The CP for all three forages exceeded the range of 7 to 8% CP suggested as a lower limit below which consumption by ruminants and microbial activity in the rumen would be affected (Van Soest, 1994). It has been reported that the CP concentration of L. leucocephala varies between 22 to 30% (Garcia et al., 1996). The values of CP found in this study are in the upper range values and similar to those given by Amjad et al. (2002) because the forages used in this study were leaves (petioles and blades) without stems. Garcia et al. (1996) reported a mean value of CP of 29% for leaves versus 22% for stems.
18In the studies of Peters (1992) and Mani et al. (1992), the CP concentration of S. guianensis forage varied between 6.3 and 10.6% DM in the dry season. Our value falls in the upper range of these values but is lower than those given by Risopoulos (1966) for forage of this species from Yangambi in DR Congo, highlighting important regional differences in soil type, age, and climatic conditions in such comparisons. The CP concentration of A. rhomboideus leaves in the present study is in the same order of magnitude as the values found in Nigeria by other authors for Adenodolichos paniculatus forage in dry season (Wolfgang, 1990; Omokanye et al., 2001). In this study, the CP concentration of A. rhomboideus was lower than for L. leucocephala but higher than for S. guianensis. This difference may arise from the fact that both L. leucocephala and A. rhomboideus species are plants that develop well in the dry season, while S. guianensis is a seasonal plant. The differences in CP concentrations between these browses are probably due to differences in protein accumulation during growth. In the case of mature herbage, nutrient concentrations are generally highest in young material and then decline with advancing maturity. The decline can be both substantial and very rapid.
19According to Garcia et al. (1996), L. leucocephala forage is rich in ADF (34.1–36.1%) and NDF (49.3–64.4%). This study found a lower value than those reported by Garcia et al. (1996), Abubeker et al. (2008), and Ngwa et al. (2000), which are similar to those reported by Boukila et al. (2005) and higher than those found by Mtenga et al. (1994) for NDF. The ADF values found in this study are similar to those reported by Boukila et al. (2005) and lower than those of Ngwa et al. (2000). The differences found in this study are probably due to soil types, plant varieties, climate, and parts of the plant used. The leaves, which are lower in fibre than stems, were used. The ADF and NDF concentrations of S. guianensis forage vary between 37 to 61% and between 42 to 72%, respectively (Mani et al., 1992; Matizha et al., 1997; Ladeira et al., 2001; Valarini et al., 2006). Our results fall in these intervals. The ADF and NDF concentrations of A. rhomboideus forage found in this work are higher than those found by Wolfgang (1990) for A. paniculatus. These differences may arise from differences in plant species, soil, and climate conditions.
20The results obtained in this study show that ADF and NDF contents of A. rhomboideus and, to a lesser extent, S. guianensis, reach the recommended amount, in contrast to the values for L. leucocephala. The ADF fraction for all forages was about 50% of the NDF, which is indicative of high levels of hemicellulose.
21Digestibility values were generally high, and better in L. leucocephala and S. guianensis forages than A. rhomboideus forage. Crude protein digestibility is related to the CP in forage (Lopez et al., 1998). Furthermore, San Martin et al. (1989) observed protein digestibility of 61.9% in sheep for diets with 10.5% CP and the digestibility declined to 36.1% in sheep with a decrease in diet CP to less than 7.5%. These values are not in agreement with the finding in the present study, which revealed higher CP digestibility for S. guianensis (58.3%) than A. rhomboideus forage (42%), though the CP content of A. rhomboideus leaves was significantly higher than that S. guianensis forage. The first explanation is that the nitrogen in A. rhomboideus may be associated with lignified cell wall to form a bulk of rumen UDP that is unavailable for post-ruminal digestion. A second explanation is that cell wall degradability of the forage may affect the overall CP digestibility. A third explanation is that the tannin component was at a level that could impact some qualities of ruminal UDP by enhancing the utilization of its protein due to a potentially higher amino acid flow to the small intestine (Meissner, 1997). It was shown that the tannin component of Sanguisorba minor depressed ruminal CP degradation but increased the passage of non-ammonia nitrogen in the small intestine (Acheampong-Boateng, 1991).
22Organic matter and DM digestibility were higher for L. leucocephala and S. guianensis than A. rhomboideus. The results are higher than those reported by Garcia et al. (1996) and Abubeker et al. (2008) but similar to those given by Nguyen (1998) for L. leucocephala. In subhumid Nigeria, Peters (1992) found that the DM digestibility of S. guianensis and S. hamata averaged 50% or less throughout the dry season. Little et al. (1984) reported S. guianensis DM digestibility close to 50% (range 20–71). The DM digestibility found in this study is higher than the value given by others (Little et al., 1984). Wolfgang (1990), in studies on a leguminous forage plant of dry season belonging to the same genus (A. paniculatus), found a lower DM digestibility value than that found in this study for A. rhomboideus.
23Neutral detergent fibre digestibility gives us accurate estimates of total digestible nutrients (TDN), net energy (NE), and feed intake potential (Karen, 2003). Karen (2003) found that increased NDF digestibility resulted in higher digestible energy and forage intake. The results of the present study are in disagreement with this statement; despite S. guianensis having significantly higher NDF and ADF digestibility than L. leucocephala (Table 3), there was no significant difference in DM intake (Table 2) and digestible DM (Table 4) between these two species.
24Thus, increased NDF digestibility will result in higher digestible energy, and the digestibility of plant material in the rumen is related to the proportion and lignification of plant cell walls. Forages with a low NDF content (20–35%) are usually of high digestibility and species with high lignin contents are often of low digestibility. Linn et al. (1993) reported that diets containing 21% NDF from high quality forages allowed more milk production and reduce off-farm feed costs. In this study, ADF and NDF digestibility were higher for S. guianensis than for other forages and are similar to those reported by Mani et al. (1992) for S. guianensis but higher than those reported by Abubeker et al. (2008) for L. leucocephala. The digestibility of cell walls is a function of lignin concentration and composition.
25The nutritive value of forage was also considered in terms of nutrient intake. Organic matter and DM intake of A. rhomboideus forage were lower than those for L. leucocephala and S. guianensis forages, which had similar values. Crude protein intake of A. rhomboideus was similar to that of S. guianensis but lower than that of L. leucocephala, because of the lower CP content of A. rhomboideus and S. guianensis. Van Soest (1994) demonstrated that the intake of DM was negatively correlated with rumen retention time and positively correlated with ruminal volume and feed digestibility. High intake has been associated with a reduction in the extent of ruminal digestion due to decreased ruminal residence time (Staples et al., 1984). Factors other than the rate of digestion in the rumen determine the voluntary intake of foliage by ruminants. Low intakes associated with high feed digestibility may be related to the presence of compounds that are appetite depressants (tannins, alkaloids,.. ; Frutos et al., 2004). High feed intakes and low feed digestibility may be related to rapid rates of passage of feed through the rumen. Feed intake increases with the concentration of CP in the diet (Faverdin, 1999). However, CP intake was similar to L. leucocephala forage and high compared with A. rhomboideus and S. guianensis forage. According to Journet et al. (1983), voluntary intake of ADF and NDF of Gliricidia sepium forage was similar to that of S. guianensis forage and higher than that of L. leucocephala and A. rhomboideus forages. Digestible CP intake was higher for L. leucocephala and S. guianensis than A. rhomboideus.
26Adenodolichos rhomboideus forage can be used for the maintenance and, to a lesser extent, for growth, whose protein requirements are estimated at between 0.74 to 1.96 g·kg-1 BW-0.75 per day and between 0.26 to 2.2 g·g-1 live weight gain (ILCA, 1979).
5. Conclusion
27This study shows that, under the conditions of the present study, A. rhomboideus has a higher CP content than S. guianensis, but A. rhomboideus forage is less consumed compared with L. leucocephala and S. guianensis forages. The intake and apparent digestibility of all nutrients from A. rhomboideus are lower than those of L. leucocephala and S. guianensis. This is probably due to anti-nutritional factors that are present in A. rhomboideus forage. A new study should focus on evaluating live weight gain by goats on a diet of grass hay supplemented with A. rhomboideus forage and on characterization of the nutritional anti-factors (saponins, tanins, alkaloids,…) in this forage.
28List of abbreviations
29ADF: acid detergent fibre
30CP: crude protein
31dADF: digestible acid detergent fibre
32dAsh: digestible ashes
33dCF: digestible crude fibre
34dCP: digestible crude protein
35dEE: digestible ether extract
36DM: dry matter
37DMD: digestible dry matter
38dNDF: digestible neutral detergent fibre
39dNFE: digestible nitrogen-free extract
40dOM: digestible organic matter
41EE: ether extract
42FM: fresh matter
43GLM: general linear model
44ME: metabolisable energy :
45NDF: neutral detergent fibre
46NE: net energy
47OM: organic matter
48RDP: Rumen degradable protein
49TADCP: total apparently digested crude protein
50TDN: Total digestible nutrient
51UDP: undegradable protein
52W: live weight
53Acknowledgements
54The authors thank Ms Kayakez, Kisimba and Amani for technical assistance during the experiment. This study was supported by CUD (Commission Universitaire pour le Développement) from Belgium.
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