Chemical composition and in vitro organic matter digestibility of major indigenous fodder trees and shrubs in Northeastern drylands of Ethiopia

Muluken Girma, Getachew Animut¹ and Getinet Assefa²

Wollo University, P.O.Box-1145, Dessie, Ethiopia
markosethio@yahoo.com
¹ Haramaya University, P.O.Box-138, Diredawa, Ethiopia
² Ethiopian Institute of Agricultural Research, P.O.Box-2003, Addis Ababa, Ethiopia

Abstract

A study was conducted at Sekota district which is located in northeastern dry lands of Ethiopia with the objective of evaluating the nutritional qualities of the major indigenous fodder trees and shrubs (IFTSs) in an effort to fill the feed gap in the area. Conventional chemical analysis procedure and in vitro organic matter digestibility (IVOMD) techniques were used to determine the nutritional quality of the major IFTSs.

There was statistically significant variation (P<0.01) among IFTSs in their chemical composition and digestibility parameters. The nutritional values during the wet season ranged from 6.00 to 11.2%, 10.8 to 21.7%, 34.6 to 50.9%, 22.3 to 29.0%, 3.64 to 8.47% and 0.26 to 0.59 for ash, CP, NDF, ADF, lignin and coefficient of IVOMD, respectively. On the other hand these nutritional values during the dry season were found to be 7.09 to 13.0%, 8.15 to 17.6,22.5 to 27.4, 4.76 to  9.22%, and 22.7 to 49.9% respectively for ash, CP, NDF, ADF, lignin and coefficient of IVOMD. Accordingly season was found to affect the nutritional quality of the species. MOreover, the feeds were shown to decrease their CP content and IVOMD from the wet to dry season while their cell wall constituents were shown to increase. Generally, based on the nutritional parameter values identified, the IFTSs were found to be of good nutritional quality. Consequently they have great potential to fill the feed and feed protein gap in the area.

Key words: dry season, feed gap, protein gap, nutritional quality

Introduction

Feed shortage is among the prominent setbacks of the livestock sector in Ethiopia resulting in a low contribution of the sector for the nationwide gross domestic product which is in contrary to the large population of livestock species in the country. The major feed resources in the country are crop residues and natural pasture with agro-industrial manufactured feeds contributing much less (Berhanu et al 2009). The highland areas of the nation which have dominantly crop-livestock production systems are recognized to be under stress because of shrinking cultivated areas per household, land degradation and reduced feed availability (Aune et al 2001). Particularly the north eastern part of Ethiopian highlands is characterized by undulating terrain with highly weathered soils; seasonal intense rains and low vegetation cover (Teshome 1995). Thus there is an urgent need to fill the feed gap especially with protein source feed resources.

Though increased utilization of agro-industrial by-products has been reported (Benin et al 2004), they are not available, affordable or feasible for most of the farmers in the highlands of Ethiopia. Specifically to Sekota District, since the bulk of the population is depends on relief for subsistence of life supplementary feeding to animals is either very costly or unavailable. Consequently it is imperative to search for low cost and alternative feed resources for the poor farmers of the area.

 Indigenous fodder trees and shrubs (IFTSs), which can fit with the existing farming system and are well adapted with the environment and with the economic realities of farmers, are best candidates for so. The main features of such plants as a feed resource is their high crude protein content (CP). Previous studies have shown that a range of 5% to 20% CP was recorded for the browse species in tropical countries (Heneidy 1996; Le Houreou 1980; Shayo and Uden 1999). Current works in Ethiopia have also reported a range of CP content of IFTSs between 9.7% and 24.5% (Mohammed 2009; Samson 2010; Zewdie 1010).

IFTSs have been used for generations as a multipurpose resource in the area. However, due to limited input of agricultural research in the area, technologies pertaining to the systematic utilization and propagation of IFTSs have been scarce. Thus it is crucial to ameliorate the severe feed shortage of the area through efficient utilization of IFTSs by supporting the indigenous feed utilization knowledge of the local farmers with scientific research outputs. This research was done to investigate the nutritional qualities of major IFTSs in the area which will serve as a launch pad for future propagation and utilization. 

The major objective of the research was to evaluate the feed nutritive value of major IFTSs in terms of their chemical composition and in vitro dry matter digestibility.

Material and Methods

Description of the study area

Sekota district is located between 12⁰ 23' and 13⁰ 16' north longitudes and 38⁰ 44' and 39⁰ 21' east latitudes (Adefress et al 2000; CSAE 2005). The altitude varies from 1340 – 2200 meters above sea level while annual rainfall ranges between 350 – 700mm, falling mainly from July to September. The pattern and distribution of the rainfall is erratic and uneven. Average temperature ranges from 16 – 27⁰C (ZAD 1995). From the estimated total area of 305771 ha about 14% is used for crop production. About 36.4% of Sekota district is non-usable at present. Area covered by bush constitutes 37.8% of the district while only 0.01% of the area is under forest. The area allotted for grazing is only about 6.5 % (EARO 2000).

Sample collection and preparation for laboratory analysis

The major IFTSs in the area has been identified and prioritized in previous assessment of the feed resources found in the area (Muluken et al 2012). This research is a continuation of this work.  Thus according to their rank based on preference by goats, the top ten IFTSs were selected for further chemical composition analysis and in vitro DM digestibility. Sample foliage (leaves) of these species was collected in the middle of both dry season (October to May) and wet season (late June to September) from three different Peasant Administrations (Pas) which were purposively selected based on their livestock potential and abundance of IFTSs. In both seasons the collection was done from three randomly selected trees for each species and a composite sample was done. In each collection day the samples were air dried in a well-ventilated room. Moreover the samples were dried in an oven for 72 hours at 65⁰C and ground in a Willy mill to pass through 1 mm sieve and equilibrated to room temperature for 24 hours. The samples were then put in air tight paper bags and sealed for further analysis.

Nutrient composition analysis

Dry matter content of the different samples was determined by oven drying the samples at 105^oC for 24 hours. After determining the total Nitrogen (N) by the Kjeldahl method (AOAC 1990), Crude protein (CP) content was calculated as N x 6.25. Ash content was determined by complete burning of the feed samples in a muffle furnace at 500^oC overnight according to the procedure of AOAC (1990). The structural plant constituents: neutral detergent fiber (NDF), acid detergent fiber (ADF) was analyzed using the detergent extraction method (Van Soest and Robertson1985). Lignin was determined by oxidation of lignin by permanganate.

In vitro dry matter digestibility

 In vitro dry matter digestibility (IVDOMD) of foliage samples was determined by the method of Tilley and Terry (1963) as modified by Van Soest and Robertson (1985). Dried samples were ground to pass through a 1 mm screen. About 0.5 g of the samples was incubated in 125 ml Erlenmeyer flasks containing rumen fluid-medium mixture for 48 hours in a water bath maintained at 39^oC. After the first 48 hrs incubation, 35 ml of pepsin solution was added to the flasks and again incubated for another 48 hrs in a 39⁰C water bath. Shaking flasks was done at 2, 4, and 6 h after pepsin addition. 

Statistical analysis

Chemical composition and in vitro DM digestibility were analyzed using analysis of variance (ANOVA) following general linear model procedure of the statistical analysis system (SAS 2002). Means were separated using Duncan’s multiple range test (DMT).

For chemical composition analysis for each season the linear additive model was;

           Y_{ijk =} μ+T_i + ß_{j +} S_{k +} e_{ijk ,,} where;

                    Y_ijk  = response variable

                    μ   = overall mean

                    T_i = treatment effect (browse species effect)

                    ß_j   = replication effect

                    e_ij = the random error

For chemical analysis over season the linear additive model was;

            Y_{ijk =} μ+T_i + ß_{j +} S_{k +} TS_{ik +} e_{ijk ,}  where;

                    μ = overall mean 

                    T_{i =} treatment (browse species) effect

                    ß_j   = replication effect

                    S_{k =} season effect

                    TS_ik = interaction effect

                    e_{ijk =} the random error

Results and discussion

Major indigenous fodder trees and shrubs in Sekota District

According to Muluken Girma et al (2012) farmers in the nine PAs of the District identified and prioritized the major indigenous fodder trees and shrubs in the area. Totally, farmers could identify 52 species of  indigenous fodder trees and shrubs from 25 different families and the top ten species prioritized by the local farmers were presented on table 1.

Chemical composition of IFTS

Analysis of variances for chemical composition of IFTSs showed that there was significant interaction effect of species and season for all parameters except ADF and lignin. Thus values within each season are reported here. The chemical composition of the ten major IFTSs, DM, CP, NDF, ADF, lignin, and ash, during the two major seasons of the area (dry and wet), were presented on Table 2 and 3, respectively. During both the wet and dry season all the aforesaid nutritional parameters were found to vary though some species have comparable values with respect to each nutrient.

During the wet season the ash content of the browse species ranged from 5.98% in Olea africana to 11.2% in Grewia Villosa. The CP of the species was also found to vary among IFTSs.  The highest CP content was found in Grewia villosa (21.7%), while the lowest was in Carisa edulis (10.8%).  NDF content also ranged between 34.6% in Acacia lahi to 50.86% in Rhus vulgaris. Similarly a range of 22.3% to 29.0% was found in the ADF content of Zizipus spinacristi and Olea Africana respectively.  Moreover, C. edulis was found to be relatively more lignified than other species with permanganate lignin content of 8.47% while Acacia lahai was the least lignified species with permanganate lignin content of 3.64%.

During the dry season, too, there was significant difference in all the chemical composition parameters among the browse species. The ash content showed a variation between 7.09% in Olea africana and 12.4% in Acacia lahi. A maximum of 17.6% and a minimum of 8.15% CP were recorded in Zizipus spinachristi and  Carisa edulis respectively. The CP content was shown to be decreased from the amount reported during the wet season.

NDF content varies from 35.6% in Grewia spp. to 43.9% in Terminalia browni. ADF also ranged between 22.5 % and 28.6% in Grewia spp. and Olea Africana respectively.  A range between 4.76% in Zizipus spina christi and 9.22% in Carisa edulis was found for the permanganate lignin content of the species. 

In vitro organic matter digestibility (IVOMD) of IFTS’s foliage

The In vitro organic matter digestibility coefficient of IFTSs foliage collected during the wet season was found to vary between 0.26 in Rhus vulgaris and 58.7% in Grewia Spp. On the other hand a range between 0.23 in Rhus vulgaris and 0.50 in Grewia Spp. was found during the dry season.  Besides, the IVOMD of IFTSs was also subjected to seasonal variation and has shown a downward trend from the wet to the dry season

Seasonal variation in the nutritive values of IFTS

A combined analysis of variance was done to evaluate the effect of season on the chemical composition and digestibility parameters so as to identify if in case there would be a change in preference of the feeds across seasons. There were significant variations in all chemical composition parameters across season which is indicated by the highly significant effect of the interaction between season and IFTSs. Likewise, the interaction between season and species was also found to be highly significant showing the variation that the intensity of seasonal effect would have on IVOMD of IFTSs.

Correlation among chemical composition parameters and IVOMD

All the chemical compositions of plants are the intrinsic natures of each species. The digestibility parameters are known to be affected by such intrinsic natures of the feeds. Thus the chemical composition and the IVOMD have some sort of relationships which can be revealed by correlation analysis which simply tell us the existence and the degree of the relationship.

Table 5 and 8 indicate the correlation coefficient and the respective statistical significance of OM, ash, CP, ADF, NDF, lignin and IVOMD of the browse species investigated. During the wet season IVOMD was significantly and positively correlated with CP (P<0.001) and ash (P<0.05). But on the other hand IVOMD was significantly and negatively correlated with OM (P<0.05), ADF and lignin (P<0.001). The correlation coefficient between IVOMD and the rest chemical composition parameters were not statistically significant.

During the dry season also IVOMD had a positive and statistically significant (P<0.05) correlation with CP and ash constituents. But IVOMD had highly significant (P<0.001) and negative relationship with OM, ADF and lignin constituents.

Discussion

In view of their CP content which ranged between 10.8% and 21.7%, all the browse species except that of Carisa edulis were found to have a CP concentration above the threshold CP content (11-12%) required for moderate level of ruminant production (ARC 1980). Nevertheless, all the IFTSs species studied have the CP content higher than the level (6-8%) below which appetite and forage intakes are supposed to be depressed (Forbes 1995). On the other hand, in light of their nutritional function, except that of Carisa edulis, Olea africana, Rhus vulgaris and the  Combretum species all the rest have CP concentration of more than 15% which is required to support  lactation and growth (Norton 1982). Conversely, if we compare the current finding with that of the minimum concentration of CP required for lactation (12%) and growth (11.3%) supposed by ARC (1984), all species except Carisa edulis will fulfill the required CP content. Although the CP contents of each browse species reported here vary numerically from other reports, most are comparable with the CP contents of browse species reported both in Ethiopia (Bruh 2008; Mohamed 2009; Samson 2010; Zewdie 2010) and other tropical countries (El-Adawy et al 2008; Ogumbosoye and Babayami 2010; Salifou 2008).

Besides, during the wet season all of the IFTSs have an NDF content below 55% that was reported by Van Soest (1965) to limit appetite and digestibility. Similarly, based on  Singh and Oosting (1992), who categorized roughages with NDF content of 45-65% as a medium quality feed, while feeds with NDF below 45% as high quality feeds, all IFTSs studied except that of acacia tortilis, rhus vulgaris and carissa edulis, can be categorized as high quality feeds. The concentrations of the cell wall content (NDF) reported here are a bit higher than those values reported by El-Adawy et al. (2008) and Ogumbosoye and Babayami (2010) while they are lower than the values reported by Bruh (2008), Mohamed (2009) and Zewidie (2010). But generally they are comparable with the values reported by Salifou (2008) and Samson (2010).   

The values reported for the level of ADF in the current IFTSs during the wet season are comparable with the values reported by Mohamed (2009). On the other hand they are a bit lower than the values reported by Bruh (2008), El-Adawy et al (2008), and Samson (2010) while they are slightly higher than the concentrations of ADF reported by Zewidie (2010). In over all the ADF proportion of NDF was found to be higher as it is true for most roughage feeds but as it has been seen it is not to the level to affect the quality of the feed and the feed intake by ruminants.

The permanganate lignin content varied between 3.64% and 8.47% in A. lahai and Carisa edulis, respectively, which is lower than values reported by Mohamed (2009), Salifou (2008) Ogumbosoye and Babayami (2010) and Zewidie (2010). Lignin is completely indigestible and it forms lignin-cellulose/hemicelluloses complexes (Kellems and Church 1998) making the cell wall content unavailable to microbial enzymes (McDonald et al 1995). Nevertheless, the amount of lignin content of all browse species investigated was found to be less than 10% which was reported to limit DM intake (Reed et al 1986).

In the dry season, too, except Carisa edulis all the browse species could fulfill the lower threshold concentration of CP content (11-12%) required for moderate level of ruminant production (ARC 1980). On the other hand, like the wet season all the IFTSs species studied have the CP content higher than the level (6-8%) below which appetite and forage intakes are supposed to be depressed (Forbs 1995). But, in view of their nutritional function, only Zizipus spinacristi, Acacia tortilis and Acacia asak are the species that can fulfill the CP concentration of more than 15% which is required to support lactation and growth (Norton 1982). Concerning their NDF content all have a concentration below 55% that was reported by Van Soest (1965) to limit appetite and digestibility. Moreover, in light of their NDF (Singh and Oosting 1992) and ADF content (Kellems and Church 1998) all feeds can be categorized under high quality feeds. Their lignin content was also found below the level to affect feed intake (Reed et al 1986).

While the numerical difference in the nutrient content difference of the species was shown on table 3 and 4, the combined analysis  revealed that the effect of season on the nutrient content of the feeds was found to be highly significant (P<0.05) except in the case of lignin. The tendency of the variation was in a decreasing manner for the parameters CP, NDF, and ADF, while it is in an increasing manner for the case of ash and lignin. Such kind of variation across season was also reported by Aganga et al (2000), Gebreyohanes et al (2005), Samson (2010), and Teferi (2006). Moreover the highly significant effect of the interaction between season and species is an evident for the highly variable response of the different species for seasonal variability. In other word, though season has significant effect on the chemical composition parameters of the different species, the degree of its effect varies across the species.

As it is evidenced from the CP content variation of the species across the two seasons (figure above), the species were affected by season in different intensity. During the wet season Grewia spp. was higher in its CP content (21.71%), but during the dry season the CP content was reduced to 14.9% (a reduction of 6.84%) and became third in its order. On the other hand Zizipus spina Christi which was second in its order with CP content of 19.6% during the wet season became first in its order during the dry season with the CP content of 17.6% (a reduction of only 1.99%).  Such variation in response to seasonal variation could be attributed to their variation in root depth, degree of nutrient dilution and resistance to leaching.

The in vitro organic matter digestibility coefficients of the IFTSs were varied between 0.26 and 0.59%. The higher digestibility could be partially attributed to the higher CP content of the feeds. But the lower digestibility records might be associated with higher proportion of NDF, ADF, and lignin (Balogun et al 1998; Buxton and Redfearn, 1997; McSweeney et al 1999; Moore and Jung 2001; Norton 1998). Moreover, though the anti-nutritional factors analysis is not included in this work, such factors might have their own share in affecting digestibility of the IFTSs which are mostly known to have relatively higher amount of anti-nutritional factors (ANF) like tannins (Kumar 1992). This would be true especially for those feeds which have relatively higher amount of CP content which in turn is known to favor high digestibility. The results found in this work are lower than earlier reports by Sanon (2007) and Zewdie (2010). But they are comparable with Ogumbosoye and Babayami (2010).

With respect to the relationship IVOMD have with ADF, CP, and lignin, this report is in line with what Teferi (2006) has reported. But with respect to the relationship between IVOMD and NDF the non-significant relationship reported here is different with the significant relationship report in the aforesaid investigation. The inverse relationship between cell wall constituents and digestibility of feeds is a well-established fact (Van Soest 1982; McDonald et al 1995). Thus the statistically significant and negative relationship which IVOMD showed with ADF, lignin and OM was as expected.

Conclusions

• The finding of this investigation has shown that the IFTSs investigated are well diversified with respect to their families. There was also great variability among the browse species in their chemical composition and digestibility parameters. Fortunately having a CP content between 8.15 and 22.71%; NDF content between 34.6 and 50.86%; ADF Content between 22.32 and 28.99%; Lignin (pm) content between 3.64 and 9.22% and IVDMD values between 22.70 and 58.72% all the browse species investigated could be categorized as high quality feeds. Provided that the appropriate entry point is identified, the high nutritional quality of the species investigated can be utilized to ameliorate the ever-increasing feed shortage of the area. However their future utilization and management needs some complementary and additional investigations.

  
  

• Most importantly the comparative advantage and the farmers’ priority of the IFTSs among their multiple uses should be investigated since the future development and efficient utilization of these trees and shrubs would rely up on the local peoples’ farming objective. Besides, the appropriate entry point should also be identified with respect to the prevailing socioeconomic and environmental realities of the area.

  
  

• The level of the ANFs which have great implication on the nutritive values of the browse species should be investigated to complement the data generated on their chemical composition and digestibility parameters. Moreover the in vivo characterization of the foliage from the top quality species and feeding trials should follow to further characterize the species as a ruminant feed and to identify the potential role these species can play in filling the feed gap during the dearth period. Furthermore, the fruits and pods of the IFTSs which can be good sources of supplementary feeds especially during the dry season should be investigated for efficient utilization of the species.

Acknowledgement

The authors of this paper would like to appreciate those who had their own share in making this research possible. The first profound appreciation and respect goes to the Ethiopian rural capacity building project for funding the whole cost of the research. Our deepest gratitude also goes to Sekota Dryland Agricultural Research Center (SDARC) for facilitating the necessary financial and logistic services during the field work. The last but not the least appreciation goes to the staff members of SDARC; Birihan Abebe, Adane Wibet, Amoke Belayneh and Sisay Mengistu for their invaluable contribution in the actual data collection activities in the undulating terrains of Sekota District which would be of difficult to achieve without their keen participation.

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Received 27 December 2014; Accepted 17 January 2015; Published 4 February 2015

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