Nutrient composition of selected indigenous tree browses in Central Equatoria State of the Republic of South Sudan

J L I Mangara¹, A Y Guliye, P K Migwi and J O Ondiek

Department of Animal Production, Faculty of Agriculture, Dr. John Garang Memorial University of Science and Technology, Bor, South Sudan.
loromangara@gmail.com
¹ Department of Animal Science, Faculty of Agriculture, Egerton University, Kenya.

Abstract

Indigenous browse tree leaves fromAcacia nilotica, Balanite aegyptiaca, Cumbretum adenogonium, Sclerocarya birrea and Ziziphus spina-christi were evaluated for the nutritive potential (chemical composition and mineral profile). All variables studied varied between the tree browses. Cumbretum adenogonium and Z. spina-christi had the highest CP values. Cumbretum adenogonium had high CF,B. aegyptiaca had high NDF and ADF as well as S. birrea with high ADF.

The browses species had phenolic and tannin contents higher than 50 g kg ^-1 DM, the maximum tolerable limit in ruminant nutrition (except B. aegyptiaca and Z. spina-christi) which had significantly (P < 0.05) lower total extractable phenols (TEP). Balanite aegyptiaca had (p < 0.05) lower total extractable tannins (TET) while C. adenogonium and B. aegyptiaca had significantly (p < 0.05) lower total condense tannins (TCT). The Macro and Micro elements differed significantly (P < 0.05) among the browse tree species. Based on the composition, it is concluded that C. adenogonium and Z. spina-christi had the best nutritive potential as dietary sources to supplement low quality forages.

Key words: browses, dietary sources, dry season, livestock, nutritive value

Introduction

Livestock is an important source of livelihood in South Sudan. Feed stuff of high nutritive value promote high levels of production. Browse leaves form a natural part of the diet for ruminant livestock species and thus have been traditionally used as sources of feed for livestock in Asia, Africa and the pacific (Le Houreou 1980a). Browse trees and shrubs provide nutrition to ruminant livestock especially in the dry season or during drought period when both quantity and quality of grasses decrease (Mogotsi et al 2015). The browses may be used either as a complete feed or as a supplement to other low quality forages. Browse trees and shrubs possess the desirable agronomic characteristics and high nutritive value to qualify as forage (Norton 1994).

The nutritive value of a feed is determined by its ability to provide necessary nutrients for animal maintenance, growth, production and reproduction. However, in some tree species, there are anti-nutritive factors that may limit it use by livestock. Chemical composition of the feed alone is an inadequate indicator of nutritive value as there is variability in nutrients available. Modern concepts of feed evaluation require that quality be assessed in terms of the capacity of the feed to supply nutrients in proportions to meet particular productive functions (Leng 1986). Although proximate analysis is a useful measure of nutritive content of forages, analysis based on detergent extraction (NDF, ADF and ADL) are more useful (Gohl 1981). Despite existence of a wide range of browses in the Republic of South Sudan, there is scanty information available on their nutritive contents and animal performance. Therefore, the aim of the current study was to determine the chemical composition and the anti-nutritive component of selected indigenous tree browses native to Central Equatoria State of South Sudan.

Materials and methods

Study area

The study was conducted in Central Equatoria State (CES) of the Republic of South Sudan (RSS). The CES lies between latitudes 30^o 30 and 60^o North and 30^o 30 and 32 ^o East at the extreme Southern parts of the Republic of South Sudan (Figure 1). The State has a hilly topography with a humid climate. It receives a rainfall with an average of about 1000 mm per year between April and November, making it a unimodal type of rainfall. The period between December and March is dry season. The CES is inhabited mainly by agro-pastoral tribes undertaking subsistence crop farming and livestock keeping. Livestock reared include cattle, sheep, goats, pigs and poultry.

Figure 1. Map of the study area (Central Equatoria State) in the Republic of South Sudan. Source: Republic of South Sudan Towns and States Map.

Selection of Samples

Samples from 5 indigenous tree species commonly browsed by ruminant livestock in Central Equatoria State of South Sudan were selected for analysis. Selection of the 5 browses was based on the recommendations of a field survey involving livestock owners in the State which identified the most common and preferred browses by the livestock. Sampling was done during the dry season (December – March), because this is the time of the year when browse species are important for grazing. The selected species are;Acacia nilotica, Balanites aegyptiaca, Combretum adenogonium, Sclerocarya birreaand Ziziphus spina-christ.

Collection and preparation of the samples

Leaves of the most preferred indigenous tree browses were obtained by hand plucking/clipping between December to March in three purposively selected counties of Juba, Yei and Kajo-keji in CES. Samples of the same tree species were collected in different parts of the selected area. The leaf samples collected were allowed to dry for seven days in shade to avoid wastage. Thereafter, the leaves were ground through a 1mm screen and packaged in 1kg plastic bags for analysis.

Chemical Analysis of the samples

The analysis of the samples for proximate composition was done at the Animal Nutrition laboratory of the Department of Animal Sciences, Egerton University, Kenya. Ground leaf samples of the selected browses were analysed for proximate composition: dry matter (DM), crude protein (CP), ether extracts (EE), and ash, according to the standard methods of AOAC (1990). The fibre component was analyzed for Neutral detergent Fibre (NDF), acid detergent Fibre (ADF) and acid detergent lignin (ADL) according to the method of Van Soest et al (1991). Mineral analyses were carried out using atomic absorption spectrophotometer (AAS) at Kenya Agricultural and Livestock Research Organization (KALRO), Njoro, Kenya. The Macro elements determined were: Calcium (Ca), Phosphorous (P), Sodium (Na), Potassium (K), and Magnesium (Mg); whereas the Micro elements were: Copper (Cu), Zinc (Zn), Iron (Fe), Cobalt (Co) and Manganese (Mn).

Phenolic compounds were extracted following the procedures described by Makkar (2003). Total extractable phenols (TEP) were determined according to the method of Julkunen-Tiitto (1985) using the Folin Ciocalteu reagent and tannic acid as standard. Total extractable tannins (TET) were determined by the Follins-Dennis spectrophotometric method (Pearson 1976). In summary, Five milliliters (5ml) of the extracted supernatant was measured into 50ml test tube and diluted with 35ml of distilled water. Standard tannin solution (tannic acid) 5ml and 5ml of distilled water were measured into separate test tube diluted with 35ml distilled water to serve as standard and blank. Then, Follin-Dennis reagent 1ml was added followed by 2.5ml of sodium carbonate solution. The content of the tubes was made up to the mark and incubated for 90 minutes at 37^oC. Thereafter, the absorbance was read at 760nm with the reagent blank at zero. The amount of TET was calculated by the formula below:

Total extractable tannin

Where; Va = weight of the test sample, = Absorbance of the test sample.

As = Absorbance of the standard tannin solution, = concentration of standard mg/ml.

vf = Volume of the extract analysed, = Dilution factor where applicable.

Total Condensed tannins (TCT) was measured using the butanol-HCl assay (Porter et al 1986), with the modifications by Makkar (2003) as described by Iqbal et al (2011). Half a milliliters (0.5ml) of the extract diluted with 70% acetone was measured into glass test tube, 3ml of the butanol-Hcl and 0.1ml of the Ferric Sulphate solution was added to the tubes. The tubes were vortexed and placed on water bath at 60-70 ^oC for 50 minutes. After the tubes were cooled, absorbance was recorded at 550nm. The absorbance of the unheated tubes (blank) was subtracted from the absorbance of the heated tubes. Therefore, TCT (%DM) were calculated as follows:

Total Condensed tannins (TCT) % = A 550nm x 78.26 x DF/sample DM%.

Where; A550nm = absorbance of the sample measured, DF = Dilution factor where applicable. All chemical analyses were carried out in triplicate.

Statistical analysis

The results of the proximate composition, fibre, mineral and anti-nutritive composition were subjected to analysis of variance (ANOVA) using General Linear Model Procedures (proc glm) of statistical package of SAS (2002, version 9.0). All analysis were based on general statistical model: Y_ij = µ + S_i + S_e ; where, Y_ij is the general observation on all variables, µ is the overall mean due to all observations, S_i is the effect of i^th browse species and S_e is the standard error of means. Significant means were separated using least significant difference (LSD) test.

Results

Chemical composition

Results of the chemical compositions of the tree browses are presented in Table 1. Acacia nilotica, B. aegyptiaca and C. adenogonium had relatively high dry matter (DM) content than Z. spina-christi and S. birrea, respectively. The DM values for A. nilotica, B. aegyptiaca and C. adenogonium were significantly (P < 0.05) different from Z. spina-christ and S. birrea (Table 1). The OM content of B. aegyptiaca is significantly (P < 0.05) higher than C. adenogonium, Z. spina-christ, A. nilotica and S. birrea (Table 1). Cumbretum adenogonium and Z. spina-christ had high CP content which was significantly higher (P < 0.05) than A. nilotica and S. birrea but not significantly different (p < 0.05) from B. aegyptiaca.

Balanite aegyptiaca and C. adenogonium had relatively high CF content. Ziziphus spina-christi had moderate; and A. nilotica and S. birrea had low CF (Table 1). Fat (EE) content of the browses ranged from 28.7 to 47.6 gkg^-1DM in B. aegyptiaca and C. adenogonium, respectively. The later had significantly (P < 0.05) higher fat content thanZ. spina-christ, S. birrea, A. nilotica and B. aegyptiaca (Table 1). Ash content of the browses studied were significantly (P < 0.05) different from one another (Table 1). Balanite aegyptiaca and S. birrea had high NDF, ADL and ADF, respectively. All the browse species evaluated had low fiber fractions indicated by lower NDF values of less than 500 gkg ^-1DM (Table 1). The crude protein trend of the selected indigenous tree browses is indicated in figure 2.

Figure 2. Crude protein DM percentage of selected indigenous browse species

Phenolic content

Results on phenolic and tannin contents are presented in Table 2. Browse tree leaves had low phenolic and tannin contents (Table 2) whereas, A. nilotica and S. birrea had the highest (P < 0.05) values for TEP, TET and TCT (Table 2). Balanite aegyptiaca had significantly (P < 0.05) lower phenolic and tannin contents compared to other browses, while C. adenogonium had significantly (P < 0.05) lowest TCT (4.2 mg/g DM) (Table 2). The condense tannins percentage of the browses is indicated in figure 3.

Figure 3. Condense tannins percentage (%) of selected indigenous browse species

Mineral composition

Mineral composition of the browse leaves are presented in Table 3. Browse tree species had high mineral contents.Ziziphus spina-christi had high (P < 0.05) level of Ca.Cumbretum adenogonium, A. nilotica and B. aegyptiaca had (P < 0.05) high mineral composition for P, Na, K and Mg, respectively compared to other browse species. On the other hand, S. birrea and Z. spina-christi had (P < 0.05) lower levels of Ca, P and K. Micro elements content ranged from 4.96 to 2701 mgkg^-1DM. Higher levels of micro elements were found in all the browse species. Co had high mean (2701 mgkg^-1DM) compared to other micro elements.

Discussions

Proximate and fibre composition

The proximate composition in terms of CP, OM, DM, fibre and lignin contents of the browses in the present study are highly variable. High CP and lower fibre composition indicate that these browses are potential nitrogen supplements for ruminants feeding on low quality roughage. Inclusion of browse leaves in the diets would overcome nitrogen deficiency and could improve on the utilization of low quality feed resources (Rubanza et al 2003) which usually have lower CP contents (30 – 50 gkg^-1 DM) (Leng 1990). The CP reported in this study is higher than the minimum requirement of 80 gkg^-1DM needed for optimal rumen microbial function (Annison and Bryden 1998).

High CP contents of browse tree leaves observed in the current study is consistent with values reported elsewhere for browse species (Abdulrazak et al 1997; Ben salem et al 1997; Abdulrazak et al 2000 and 2001; Nantoume et al 2001; Rubanza et al 2003; Ondiek et al 2010; Belete et al 2012 and Dambe et al 2015). In this study, Z. spina-christ had high CP values (201 gkg^-1DM). However, Gaiballa and Lee (2012) reported low values of CP and high levels of CF for some browse species ( Balanite aegyptiaca, Grewia mollis and strychnos spinosa) f) from South Sudan. The role of browses as nitrogen sources for ruminants, especially during dry season, is a major contribution in the tropics where other protein sources are not available or expensive. The browse forages show low to moderate fibre and lignin content (Table 1) which is a positive attribute as the feed intake and digestibility are dependent on fibre particularly, the NDF and lignin. The results on fibre fraction agree with those reported by Bakshis and Wadhwa (2004). The fibre content of browse species has been shown to be more digestible than that of grasses and crop residues (El Hassan et al 2000). This could be due to supply of nitrogen from the browse leaves that supplement the microorganisms in the rumen.

Phenolic content

In the current study, all browse trees except B. aegyptiaca and Z. spina-christ had high phenolic and tannin contents greater than the 50 mg/g DM reported to be the minimum beneficial level in ruminants (Mangan 1988). However, C. adenogonium had the lowest TCT (4.2 mg/g DM) content. Acacia nilotica and S. birrea ha had the highest phenolic and tannin concentrations (Table 2). Higher concentrations of phenolic and condensed tannins were also reported in other studies on browse species by Reed (1986), Abdulrazak et al (2000a,b), Elseed et al (2002), Rubanza et al (2003), Osuga et al (2006) and Ondiek et al (2010). Higher levels of phenolic and tannins in browses tend to lower feed digestibility and decrease nutritive values through decreased digestibility and nutrient utilization (Makkar and Becker 1996; Rubanza et al 2003 and Abdulrazak et al 2000). Several factors are associated with high phenolic and tannin concentrations in browses and these include high environmental temperatures, drought and defensive mechanism against invading pathogens (Mangan 1988; Rubanza et al 2003). Phenolic and tannin contents in browse species may vary due to different assays used and the standards used in samples analysis (Makkar and Becker 1993). On the other hand, differences in phenolic and tannin levels may be due to the stage of plant maturity, season of harvesting of browse material and the location of growth (Woodward and Reed 1989; Makkar and Becker 1998; Abdulrazak et al 2001 and Rubanza et al 2003).

Mineral composition of the selected indigenous browse species

Mineral composition of the browse tree species in the current study is high. All browse species except S. birrea had high levels of Ca (Table 3). These values agree with those reported in the same and other browse species (Abdulrazak et al 2000; Aganga et al 2000; Elseed et al 2002 and Ondiek et al 2010). The P levels corresponded well with the values reported in Balanite and Ziziphus (Ondiek et al 2010). The Ca levels in the browse leaves studied except S. birreaa were relatively high exceeding the recommended level (11 gkg^-1DM) for lactating ewes (NRC 1985), while P is lower for lactating ewes (7.7 gkg ^-1DM). Elis (1982), Elseed et al (2002) and Ondiek et al (2010) reported similar lower P values in different browses. The concentrations of Na and K were high in all the browse species. Browse trees contain high levels of Mg between 2.8 to 8.07 gkg^-1DM. The browse tree leaves studied currently indicate adequate levels for ruminant requirements. The concentrations of macro elements were higher compared to requirements suggested for growth (2.4 – 10.8gkg^-1DM Ca), pregnancy (1.4 – 3.5 gkg^-1DM Ca) and lactation (2.8 – 5.3 gkg^-1DM DM Ca) (ARC 1980 and Meschy 2000) indicating that a diet of the browse can sustain the animals. Also P, Mg, Na and K values in this study are higher compared to recommended requirements as suggested by Minson (1990), Underwood and Suttle (1999); and NRC (2001). The results on macro elements suggest that animals feeding on natural fodders in the area of study may not require mineral supplementation. The micro elements in this study indicate higher levels with the exception of Mn which was lower (Table 3). Higher values were observed for Cu, Zn, Fe, Co and Mn. These results are comparable to those reported by Ondiek et al (2010) and Rubanza et al (2003). The concentration of micro elements were higher than the amounts required for growth, pregnancy and lactation as suggested by ARC (1980), Minson (1990), Underwood and Suttle (1999), Meschy (2000) and NRC (2001); except for Mn which may need to be supplemented because of the lower values than that recommended for growth, pregnancy and lactation.

Conclusion

• Indigenous tree species in Central Equatoria State have nutritive potential as indicated by high crude protein and low fibre contents.
  
  
• Most of the browses contained high levels of phenolic and tannins greater than 50 gkg ^-1DM, the maximum tolerable limit by ruminants.
  
  
• These higher levels could decrease the nutritive potential of these browses due to effect on taste. Condensed tannins also bind enzymes and nutrients.
  
  
• The results of the study indicate that the browses would form adequate sources of mineral supplements to ruminant livestock. Browse species had mineral levels higher than their dietary requirements for ruminant livestock feeding.
  
  
• Excessive levels of Co could be harmful to livestock depending on the inclusion rate.
  
  
• These findings warrant further investigations on the practical feeding trials to guarantee adequate nutritional evaluation on these browse species.

Acknowledgments

The authors would like to express their thanks to the Department of Animal Sciences, Egerton University and the staff of the Animal Nutrition Laboratory for their assistance in the chemical analysis. Many thanks are extended to Kenya Agricultural and Livestock Research Organization (KALRO), Njoro, for assisting in facilities for carrying out mineral analyses. Finally, we are indebted to the Borlaug High Education for Agricultural Research and Development (BHEARD) of USAID for funding this work.

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Received 13 January 2017; Accepted 18 February 2017; Published 1 April 2017

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