Artículos de investigación

 

Nutritive value of morphological fractions of Sesbania sesban and Desmodium intortum

 

Valor nutritivo de las fracciones morfológicas de Sesbania sesban Y Desmodium intortum

 

Etana Debela^a,b*, Adugna Tolera^c, Lars O. Eikª, Ragnar Salteª

 

ª Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, P.O. Box 5003, N-1432, As, Norway

^b School of Veterinary Medicine, Hawassa University, P. O. Box 5, Hawassa, Ethiopia

^c Department of Animal and Range Sciences, College of Agriculture, Hawassa University, P. O. Box 5, Hawassa, Ethiopia. E-mail: etanadebela@yahoo.com

* Corresponding Author

 

Submitted December 14, 2009
Accepted October 10, 2010
Revised received June 08, 2011

 

Abstract

Nutritive value of morphological fractions of Sesbania sesban [accession 15019] anaDesmodium intortum cv. Greenleaf was estimated based on chemical composition, in sacco dry matter (DM) degradability, in vitro gas production (IVGP) and in vitro organic matter digestibility (IVOMD). In Sesbania, neutral detergent fiber (NDFom) and acid detergent fiber (ADFom) contents were higher (P<0.05) in twigs and green pods, whereas the acid detergent lignin (ADLsa) content showed the following ranking order (P<0.05): green pods > twigs > whole forage > leaves. The soluble tannins (STs) content was higher (P<0.05) in green pods and whereas the content of condensed tannins (CTs) was higher (P<0.05) in leaves and whole forage. All fractions had sufficient levels of macro and micro minerals, except sodium. Sesbania leaves and whole forage had higher (P<0.05) potential in sacco degradability (A+B) and in vitro organic matter digestibility (IVOMD). In the case oí Desmodium, the twigs had lower CP contents and leaves had lower NDFom, ADFom and ADLsa contents. The STs content was highest in leaves whereas the CTs content was higher in whole forage. The washing loss (A) was higher in twigs, while the slowly degradable fraction (B) was higher in greed pods. In the view of the nutrient contents, both Sesbania and Desmodium can be used as a supplement to improve the nutritional status of ruminants fed low quality roughages.

Key words: Chemical composition; in sacco DM degradability; in vitro gas production; minerals; tannins.

 

Resumen

Se estimó el valor nutritivo de diferentes fracciones morfológicas de Sesbania sesban [accesión 15019] y Desmodium intortum cv. Greenleaf empleando la composición química, degradabilidad in situ, producción de gas in vitro (IVGP), y digestibilidad in vitro de la materia orgánica (IVOMD). En la Sesbania, los contenidos de fibra detergente neutra (NDFom) y la fibra detergente acida (ADFom) fueron mayores en los rebrotes y vainas verdes, mientras que el contenido lignina ácido detergente (ADLsa) fue vaina verdes > rebrotes > follaje > hojas. El contenido de taninos solubles (STs) fue mayor en las vainas verdes y el de taninos condensados (CTs) fue mayor en las hojas y el follaje. Todas las fracciones tuvieron niveles adecuados de macro y micro minerales con excepción de su contenido de sodio. Las hojas y el follaje tuvieron una mayor degradabilidad in situ e IVOMD. En el caso del Desmodium, los rebrotes tuvieron los menores contenidos de PC, NDFom, ADFom y ADLsa. El contenido de STs fue mayor en las hojas y los CTs en el follaje. La pérdida por lavado de la fracción soluble (A) fue mayor en los rebrotes y la fracción lentamente degradable (B) fue mayor en las vainas verdes. Por su contenido de nutrientes, tanto la Sesbania como el Desmodium pueden ser empleados como suplemento de rumiantes consumiendo forrajes de baja calidad.

Palabras clave: Composición química; degradabilidad in sacco; producción de gas in vitro; taninos.

 

INTRODUCTION

Nutritional inadequacy limits the performance of herbivore animals during the dry season when the quality and quantity of the natural pasture declines (Tolera, 2007). Under such conditions, shrubs and legume free fodders are important sources of supplementary proteins, vitamins and minerals for livestock (Hove et al., 2001). The presence of antinutritional factors such as polyphenols in tropical forage species may reduce intake, digestibility and availability of nutrients thereby affecting productivity of ruminant animals (Makkar, 1993). However some of the polyphenols possess medicinal, e.g. anthelmitic properties (Robertson et al., 1995, Githiori et al., 2004). Among these, proanthocyanidins or condensed tannins (CTs), are widespread in nature and occur in a range of herbaceous and tree or shrubby legumes (Jones et al., 1976; Terrill et al., 1992). Condensed tannin concentrations vary both between plant species and within the same specie influenced by environmental factors (Barry and Forss, 1983; Roberts et al., 1993). They may also differ in structure and biological activity (Foo et al., 1996). CTs are commonly found in the leaves of plants, but in some forages such as white and red clover, they occur in the flower petals (Barry, 1985). This justifies the need to investigate concentrations of condensed tannins in forage species of a given environmental and geographical condition and in different parts of the forage plants.

The chemical composition and digestibility of forages are influenced by plant species, plant morphological fractions, environmental factors and stage of maturity (Papachristou and Papanastasis, 1994). Under cut-and-carry forage feeding systems practised in smallholder animal production systems, leaves and twigs are commonly used as feed for small ruminants, especially during the dry season (Karachi, 1998). Leaf loss is quite common during harvesting, transporting and storage of forages, which justifies study of morphological fractions. In Ethiopia, Sesbania sesban and Desmodium intortum are used as fodder for small ruminants (Solomon et al., 2004; Tolera, 2007). Both legumes are high-producing, short-lived perennials that are easy to establish even on low-quality soils.

Although studies have been undertaken on the chemical composition and nutritive value of Sesbania sesban hay (Solomon et al., 2003) and seeds (Hossain and Becker, 2001), and Desmodium intortum hay (Tolera and Sundstol, 2000; Nurfeta et al. 2008), information is lacking on the feeding value of different morphological fractions of these forage crops, except the chemical and mineral analysis carried out by Kabaija and Little (1988). Data on the nutritive value and CT content of each fraction of Sesbania and Desmodium are important in order to utilize both the nutritional and the anthelmintic potentials of these legume forages. Such information could provide a basis on which adequate feed rations can be established for feeding on a year-round-basis. The objective of this study was, therefore, to determine the chemical composition, in sacco DM degradability, in vitro organic matter digestibility and in vitro gas production of morphological fractions of Sesbania sesban ana Desmodium intortum.

 

MATERIALS AND METHODS

Description of study area, the forages and sample collection

Desmodium intortum cv. Greenleaf and Sesbania sesban (accession 15019), characterized by high level of CTs, were each established on one ha of land with sandy loam soils at Hawassa University (7°04' N and 38°31' E; 1650 m above sea level) in southern Ethiopia. The main rainy season extends from April to September interrupted by some dry spells in May or June with annual precipitation ranging between 1000 and 1200mm. The average minimum and maximum temperatures of the area are 12° and 27°C, respectively.

The edible parts of the forage samples from 20 individual Sesbania trees and from 12 plots (lm x lm) of Desmodium stand randomly selected from different locations on the farm were collected. The samples were cut at the green stage using a sickle and taken to a laboratory, where they were weighed and divided into two equal parts; one half was taken as whole forage representing all fractions, while the remaining half was separated into leaves, green pods and twigs. Samples were dried in a draft oven at 50C for 48 h. A portion of each sample was ground through 1.0 mm sieve using a Wiley mill (Thomas-Wiley, Laboratory Mill Model 4, Arthur H. Thomas Company, Philadelphia, PA, USA) for chemical analysis, in vitro organic matter digestibility (IVOMD) and in vitro gas production while the remaining portion was ground through 2.0 mm sieve for in sacco DM degradability.

 

Chemical analysis

Dry matter (DM), ash and acid detergent fibre (ADFom) content of the forage samples were determined using methods no. 934.01, 942.05, 973.18) (AOAC,1990), respectively. Nitrogen (N) content was determined by the micro-Kjeldahl method and crude protein (CP) was calculated as N x 6.25. Phosphorus (P) contents were determined by continuous flow analysis (ChemLab, 1981). Neutral detergent fibre (NDFom) was analyzed according to Van Soest et al. (1991). Sulfite and a-amylase were not used as reagents in the determination of NDF. Both NDFom and ADFom were reported exclusive of residual ash. Acid detergent lignin (ADLsa) was determined in ADF residues (Robertson and Van Soest, 1981). The contents of condensed tannin (CT) was determined by heating NDFom samples at 95°C for one hour in n-butanol containing 5% concentrated HC1, after which the absorbance was read at 550 nm (Reed et al., 1985). Soluble tannin (ST) was measured according to the method of Porter et al. (1986).

Mineral contents of the forage fractions were determined by a wet ashing procedure using H₂SO₄ and H₂O₂. The samples were analyzed for the macro minerals calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg) and the micro minerals iron (Fe), manganese (Mn), copper (Cu), zinc (Zn) and cobalt (Co) by atomic absorption spectrophotometer (Perkin-Elmer, model 2380, USA).

 

In sacco DM degradability

Approximately 2.5 g sample was weighed into nylon bags (6.5 cm x 14 cm, 41um mesh size, Polymon, Switzerland) and the bags were inserted into the rumen of three fistulated, mature sheep fitted with a permanent rumen cannula. The animals were housed in individual pens, and were each offered 800 g mixture of Rhodes grass and Desmodium or Sesbania hay supplemented with 200 g of concentrate a day in two equal feedings. After an incubation of 4, 8, 16, 24, 48, 72 and 96 h, the bags were removed from the rumen and immediately rinsed in cold water to stop fermentation and to remove the feed particles adhering to the bags. Then, the bags were transferred to a domestic washing machine and washed for 30 min in three cycles (15, 10 and 5 min, respectively) at 22-25°C, dried to a constant weight at 60°C for 48 h, and weighed.

The exponential model of 0rskov and McDonald (1979) was used to describe the degradability constants of the feed samples: Y = a + b (l-e^-ct) where, Y is DM degradation rate (%) at time /. Since washing loss (A) is higher than the estimated soluble fraction (a), the lag time was estimated according to McDonald (1981) by fitting the model Y = A for f ≤ t₀, Y = a + b (l-e^-ct) for t > t₀ and the degradation characteristics of the samples was defined as: A = washing loss (representing the soluble fraction of the feed); B = (a+b)-A, i.e. the insoluble but slowly degradable fraction; c = the rate of degradation of fraction B per hour at time / and the lag phase (L)=(l/c) log [b/(a+b)-A)]. The effective DM degradability was calculated as ED = A+[Bc/ (k+c)], where A, B and c are as described above and k is rumen outflow rate, which was assumed to be 0.05h^-1 (Dhanoa, 1988; Ørskov and Ryle, 1990).

 

Invitro organic matter digestibility and gas production

In vitro organic matter digestibility (IVOMD) was determined by the method of Tilley and Terry (1963) as modified by Van Soest and Robertson (1985), which replaces the second-stage pepsin digestion with a neutral detergent extraction. In vitro gas production of the forage fractions was determined following the procedure of Menke and Steingass (1988). About 200 mg of dry sample (milled through a 1.0 mm sieve) was incubated in vitro with rumen fluid in a calibrated glass syringe of 100 ml in triplicate. Vaseline was applied to the pistons to ease movement and prevent escape of gas. The syringes were pre-warmed at 39°C before addition of 30 ml of rumen liquor and buffer mixture into each syringe. The syringes were shaken gently 30 min after the start of incubation and every hour for the first 10 h of incubation. Blanks with buffered rumen fluid without feed sample were also included in triplicate. All the syringes were incubated in a water bath maintained at 39°C. Gas production was recorded after 3, 6, 12, 24, 48, 72, and 96 h of incubation. The gas production characteristics were estimated by fitting the mean gas volumes to the exponential equation of 0rskov and McDonald (1979): G = a + b (1-e ^-ct), where G is the gas production (ml/200mg OM) at time /, a is the intercept of the gas production curve, b is the extent of gas production, a + b is the potential gas production (ml/200 mg OM), and c is the rate constant of gas production (Blümmel and Ørskov, 1993).

 

Statistical analysis

Chemical composition, in sacco DM degradability, IVOMD and gas production data were subjected to analysis of variance using the GLM procedure available in the Statistical Analysis System (SAS, 2001). Duncan's multiple range tests was used for means separation. Correlation between chemical compositions, in vitro gas production parameters, IVOMD and in sacco degradation characteristics were performed with the Pearson product moment correlation procedure (SAS, 2001). No statistical analyses were undertaken on mineral contents of the morphological fractions of the forages.

 

RESULTS

Chemical composition

The DM content oí Sesbania (Table 1) was the highest (P<0.05) in twigs and the lowest in the whole forage whereas the ash content was significantly (P<0.05) higher in leaves and twigs than in green pods and whole forage. No differences were found in CP and ADF-ash content between fractions. The NDFom and ADFom contents were significantly (P<0.05) higher in twigs and green pods compared with leaves and whole forage. The ADFom content was the lowest (P<0.05) in leaves and the highest in twigs and green pods. The ADLsa values showed the following declining trend (P<0.05) among the different fractions: green pods > twigs > whole forage > leaves. The concentration of STs was significantly (P<0.05) lower in the twigs than in the leaves and green pods, whereas the content of CTs was significantly (P<0.05) higher in leaves and whole forage than in twigs and green pods.

Desmodium twigs had significantly (P<0.05) higher ash content than other fractions (Table 1). The CP was the highest in leaves and the lowest in twigs whereas the NDFom content was significantly (P<0.05) lower in leaves than in the other fractions. The ADFom content showed the following ranking order among the different fractions: twigs > green pods and whole forage > leaves. The ADLsa content was significantly (PO.05) lower in leaves than in the other morphological fractions. The concentration of soluble tannins was the lowest (P<0.05) in green pods and the highest the in leaves whereas the CT content was significantly (P<0.05) higher in whole forage than in twigs.

The macro and micro mineral contents of the morphological fractions are shown in Table 2. All the minerals, except sodium, were found to be within or above the range required by ruminant animals.

 

In sacco DM degradability

The DM disappearance and degradability parameters of the different morphological fractions of Sesbania and Desmodium are given in Figure 1a and in Table 3. Leaves and whole forage from Sesbania did not differ significantly in their DM disappearance (P>0.05), except at 4 hrs, and maintained significantly (P<0.05) higher DM disappearance than other fractions at all incubation times (Figure 1a). Green pods showed significantly (P<0.05) lower DM disappearance values at all incubation times than twigs, leaves and whole forages. In the case of Desmodium, however, there were no significant differences in DM disappearance between the different morphological fractions at any incubation time.

 

The soluble or rapidly degradable fraction (A) and the potential degradability (A+B) differed significantly (P<0.05) between morphological fractions of Sesbania in the following order: leaves > whole forage > twigs > green pods. The slowly degradable fraction (B) was significantly (P<0.05) higher in twigs and whole forage than in leaves, which in turn showed higher B values than the green pods. There were no significant differences between fractions with respect to degradation rate (c) or lag phase (L). The effective degradability (ED) was higher (P<0.05) in leaves and whole forage than in twigs and green pods.

There were no differences among Desmodium fractions (P>0.05) in potential degradability (A+B), effective degradability (ED) and degradation rate (c). The washing loss (A) was higher in twigs than in whole forage, which in turn had higher A values than leaves and green pods. The slowly degradable fraction (B) was significantly (P<0.05) higher in green pods than in twigs whereas the lag time was lower in the green pods than in the other fractions.

 

Invitro organic matter digestibility and gas production

In vitro organic matter digestibility of the two forages is shown in Table 3. The IVOMD of Sesbania was significantly (P<0.05) higher in leaves and whole forage than in the twigs and the lowest (P<0.05) value was found in green pods. Fractions of Desmodium did not show significant differences (P>0.05) in their IVOMD digestibility values.

Gas produced from the soluble component (a) was higher in leaves and whole forage than in twigs and green pods of Sesbania (Table 4). The extent of gas production due to the insoluble but slowly fermentable component (b) was highest in twigs and lowest in green pods with intermediate values in leaves and whole forage, whereas the rate of gas production (c) and potential gas production (a+b) were significantly (P<0.05) lower in green pods than in the other fractions. Leaves, twigs and whole forage of Sesbania produced significantly (P<0.05) higher volumes of gas at all incubation times than did green pods (Figure 2a). All fractions showed rapid gas production between 12 and 24 h of incubation.

 

Gas production from the soluble component (a) of Desmodium was the highest in green pods and the lowest in whole forage (Table 4) .The extent of gas produced from the insoluble but slowly fermentable component (b) was significantly (P<0.05) higher from twigs and whole forage than in leaves and green pods. The rate of gas production (c) was higher in twigs and green pods than in leaves and whole forage, whereas the gas production potential (a+b) was higher in twigs than in the other fractions. The leaves and whole forage produced less volume of gas than the twigs and green pods from 3 to 12 h of incubation (Figure 2b). The volume of gas produced from 12 h onwards was highest in twigs and lowest in the leaves of Desmodium. All Desmodium fractions showed rapid gas production between 12 and 24 h of incubation (Fig 2b).

Correlations between chemical composition, in vitro OM digestibility, in sacco DM degradability and gas production characteristics.

Correlation between chemical composition, IVOMD, in sacco DM degradability and gas production characteristics are given in Table 4. NDF, ADF and ADL were negatively correlated (P<0.05) with IVOMD, the readily degradable fraction, effective degradability, potential degradability, rate of dry matter degradation and the readily fermentable components of the forage fractions. Soluble tannin was negatively correlated with the rate and extent of gas production and with the potential of gas production (PO.01) from the forage fraction components. Condensed tannins were negatively correlated with NDF and ADF but positively correlated with all degradability parameters, CP and IVOMD. Positive correlation was observed between in sacco DM degradability and in vitro gas production characteristics and IVOMD.

 

DISCUSSION

Chemical composition

Leguminous forages have been used as feed for livestock in many regions of the world, mainly because of their high protein contents throughout the year (Tolera et al., 1997; Tolera, 2007). In this study, crude protein contents were in agreements with earlier findings (Kabija and Little, 1988; Tolera and Sundstol, 2000; Solomon et al., 2004). The CP contents of Sesbania fractions varied from 194 g/kg DM in twigs to 297 g/kg DM in leaves, whereas that of Desmodium fractions varied from 133 g/kg DM in twigs to 275 g/kg DM in leaves. Thus, the different fractions of the two forages had moderate to high levels of CP, which indicates that all the morphological fractions of the two forages could provide supplemental protein to ruminants offered diets low or deficient in CP, especially at times when the quality and quantity of available feed is low.

Utilization of CP in leguminous forages may be negatively affected by the contents of CTs, alkaloids and saponins (D'Mello, 1992; Kumar and D'Mello, 1995). Contents of alkaloid and saponin were not determined in this study, but the concentrations of CTs in all fractions of Sesbania were higher than previously reported (Solomon et al., 2003). On the other hand, the CTs content of Desmodium fractions was lower than earlier reports for Desmodium intortum hay (Tolera and Sundstol, 2000). Differences could be due to changes in the extractability of tannins with season, changes in leaf morphology, moisture content or chemical composition (Hagerman, 1988).

The content and type of cell wall fractions in plants will influence DM intake and digestibility of the forage (Buxton, 1996; Bakshi and Wadhwa, 2007). The higher NDFom, ADFom and ADLsa contents in twigs and green pods of both Sesbania and Desmodium than in other fractions reflects the fibrous nature of these fractions. The ADF/NDF proportion was within the high range of 0.76 to 0.85 for Sesbania fractions and 0.80 to 0.95 for Desmodium fractions, which is indicative of high contents of cellulose and lignin and lower levels of hemi-cellulose (Abdulrazak et al., 2000). However, the mean NDF contents of whole forage from both species is close to the optimum concentration in diets of high producing dairy cows at peak lactation, and it is higher than the value recommended for fast growing ruminants (Mertens, 1994).

Information on the mineral composition of different morphological fractions of Sesbania and Desmodium is limited. The present results show that all fractions had sufficient levels of Ca, P, K, Mn, Co, Cu, Zn and Fe, which in most cases compared with the recommended requirements for all classes of animals (McDowell, 1997). Kabaija and Little (1988) reported marginal to deficient Na, Cu, and P contents in most crop residues and some forage fractions fed to ruminants in Ethiopia. And copper deficiencies has also been reported in ruminants in the rift valley of east Africa (Faye et al., 1991) as have sway back in lambs and goats in the rift valley system around Zway in Ethiopia (E. Debela, personal observation, 2007). All fractions from the two forages were, however, deficient in Na content. Provided Na is supplied Sesbania and Desmodium fractions could alleviate deficiencies of Ca, Mg, K, P, Zn, Cu, Mn, and Fe. A Ca: P ratio of 1:1 to 2:1 in the feed is considered to be adequate for farm animals other than poultry (McDonald et al., 1988). The values of all fractions in the present study were relatively closer to the 2:1 ratio (except for Sesbania leaves, which had a higher ratio).

 

Insacco dry matter degradability

The solubility of roughage, the insoluble but potentially degradable fraction and degradation rate are important factors that affect the intake of poor quality forages (Ørskov, 1994), and A, B and c values are considered to be precise predictors of feed intake, digestibility and growth rate (Tolera and Sundstol, 2001). The washing loss (A), potential degradability (A+B), effective degradability (ED) and lag time (L) values of Desmodium fractions in this study were all higher than the values reported for Desmodium hay (Tolera and Sundstol, 2001).

DM disappearance of Sesbania fractions decreased in the order of leaves ≥whole forage > twigs > pod. The washing loss (A), which represents the degradability of the readily soluble fraction, also followed a similar ranking order implying the varying degree of availability of the soluble components from the different fractions of the species. The higher potential degradability (PD) and effective degradability (ED) of leaves and whole forage from Sesbania could be associated with the low lignin content compared to other fractions (Table 1). The washing loss (A) obtained for all fractions from the two forages was higher than the values reported high quality forages like alfalfa and common vetch (Turgut and Yanar, 2004). The findings indicate that both roughage species may be used to improve feeding of small ruminants.

 

Invitro organic matter digestibility and gas production

The low IVOMD in twigs and green pods from the two forages is likely an effect of high fibre contents in these fractions (Table 1), as is supported by the negative correlation between fibre fractions of the feeds and IVOMD (Table 4). Conversely, the higher IVOMD in leaves from Sesbania and Desmodium and whole forage from Sesbania would be associated with higher CP and lower fibre concentrations, thus underlining the potential of these fractions to enhance the digestibility of low quality feeds fed to animals when other feed resources are scarce.

The in vitro gas production in this study could not rank the morphological fractions in the same order as the in sacco DM degradability. This is in agreement with the findings of Tolera and Sundstøl (1999) who demonstrated a similar phenomenon in ranking morphological fractions from maize stover. This variation in values would be an indication of the amount of soluble fractions being fermented. Negative gas production values due to the readily degradable fraction (a) were recorded for twigs and whole forage from Desmodium. Similar negative values have been reported earlier for some grass species (Berhane et al., 2006) and were ascribed to the low soluble content that could ferment instantly. Blummel and Becker (1997) suggested, on the other hand, that negative values could be due to a lag phase in the fermentation of insoluble feed components that lead to a deviation from the exponential curve of fermentation. The relatively lower rate and extent of gas production from green pods of the two forages and leaves from Desmodium could be associated with the cumulative impact of fiber and tannin contents as both components showed a strong inverse relationship with gas production characteristics. In support of this suggestion are the findings of Abdulrazak et al. (2000) who reported an inverse relationship between gas production and NDF and ADF contents, and those of Kamalak et al. (2005) who found a negative correlation between gas production and polyphenolics present in browse forages.

 

CONCLUSION

The different fractions of Desmodium and Sesbania have nutritive values that compare favourably to other leguminous forages available in climatic zones similar to Hawassa area of southern Ethiopia. The plants combine qualities of high nutrient content and good digestibility that makes the whole forage or the different fractions both species useful supplements to low quality roughages, particularly on smallholder farms.

 

ACKNOWLEDGEMENTS

The authors would like to thank Norwegian Agency for Development Co-operation (NORAD) for financial support.

 

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