Chemical and mineral composition, in-vitro gas production, in-sacco degradation of selected indigenous Kenyan browses

J O Ondiek, S A Abdulrazak* and E N Njoka**

Egerton University, Department of Animal Sciences, P.O. Box 536-20115, Egerton, Kenya
* Secretary/CEO, National Council for Science and Technology, P.O. Box 30623-00100, Nairobi, Kenya
** Principal, Chuka College Campus, P.O. Box 109 Chuka. Kenya
sabdulrazak@yahoo.com

Abstract

Proximate and mineral composition, in-sacco degradation and in-vitro gas production was conducted using fifteen indigenous Kenyan multipurpose tree and shrub (MPTS) leaf browse to assess their potential as goat feed. The species selected from a field survey were Maerua angolensis, Acacia brevispica, Acacia mellifera, Acacia tortilis, Acacia hockii, Zizyphus mucronata, Grewia bicolor, Acacia elatior, Acacia nilotica, Balanites aegyptiaca, Acacia senegal, Acacia abyssinica, Bridelia micrantha, Albizia amara and Albizia coriaria.

The CP levels ranged from 112gkg^-1DM for Bridelia micrantha to 321 gkg^-1DM for Maerua angolensis; the NDF ranged from 218 to 601 gkg^-1DM for Acacia hockii and Albizia amara, respectively. The TEPH and TET were in the range of 1.52-26.4 and 0.301-24.4gkg-1DM, respectively. The major minerals Ca, P, Mg, Na and S were in the ranges of 6.51-28.1, 0.838-3.18, 0.442-8.51, 0.318-0.711 and 1.12-2.45gkg^-1DM, respectively. The microelements varied widely (mgkg^-1DM) as follows: Fe (51.3-267), Mn (13.8-38.5), Cu (4.81-74.9), Mo (13.9-43.4), Co (1.76-17.4), Zn (12.2-93.2) and Se (19.5-124). In-sacco DM degradation at 48hrs shows Zizyphus mucronata was highest followed by Maerua angolensis with degradability of 93.3% and 88.6%, respectively. Gas production (volume (ml)/200mgDM) levels (a+b) ranged from 19.2 to 52.2 in Bridelia micrantha and Maerua angolensis, respectively. The overall levels of nutrients and degradation showed variations but most of the forages were moderate to high in the nutrient composition and degradability parameters. The ranking of the forages in order of increasing nutritive value into three categories of five species was as follows: low (Bridelia micrantha< Albizia amara< Acacia hockii < Acacia nilotica< Acacia tortilis); medium (Acacia abyssinica< Grewia bicolor< Albizia coriaria< Acacia elatior) and high (Balanites aegyptiaca< Acacia mellifera< Acacia senegal< Zizyphus mucronata< Maerua angolensis).

It is concluded that Maerua angolensis and Zizyphus mucronata are outstanding and they have potential for ruminant feed and more so as protein supplements to low quality tropical basal diets.

Keywords: Acacia brevispica, Acacia mellifera, Acacia tortilis, Acacia hockii, Acacia elatior, Acacia nilotica, Acacia senegal, Acacia abyssinica, Albizia amara, Albizia coriaria, Grewia bicolor, Balanites aegyptiaca, Bridelia micrantha, Maerua angolensis, nutritive value, protein, Zizyphus mucronata

Introduction

Poor nutrition caused by inadequacies in both quantity and quality of the major grass forages that are low in digestible nutrients may not supply nutrients to meet animals’ requirements (Leng 1990). This is one of the major causes of low livestock productivity in tropical areas, Kenya included. Animals consuming basal diets containing less than 7% crude protein (CP) will require supplementation for improved performance (Abdulrazak et al 1997; Ondiek et al 1999, Ondiek et al 2000), hence there is need to exploit this legume forage resource. Some acacia species including Acacia brevispica, Acacia nubica, Acacia tortilis, Acacia seyal, Acacia nilotica and Acacia mellifera have been shown to contain appreciable crude protein (134-213gkg^-1DM) and minerals (Abdulrazak et al 2000).

Useful forage MPTS are documented (Topps 1992, World Agroforestry Centre 2005) but these vary in nutritive values and, therefore, it is important to assess the local species using simple techniques like proximate analysis, nylon bag and in-vitro gas production methods. The in-vitro gas production technique as modified by Menke and Steingass (1988) is one of the useful tools for determining the potential nutritional value of feed resources consumed by ruminants, especially tree and shrub legume forages containing anti-nutritional factors such as polyphenols, tannins and polyphenolics (Woodward and Reed 1997), which may compromise the nutritive value of the fodders (Swain 1979) when consumed by ruminants. Tannins precipitate protein by forming tannin-protein complexes (Reed 1995), thereby reducing the digestibility of protein and feed dry matter (Hangerman et al 1992).

However, tannins may increase the availability of rumen undegradable nitrogen, digestible energy and minerals when fed to livestock (Ash 1990). More studies are reported for introduced forage species but the nutritional value of the abundant indigenous MPTS is scanty. The objective of this study was to assess the potential nutritional contribution of fifteen indigenous Kenyan tree browse species for local goats using proximate, in-sacco and in-vitro methods.

Materials and methods 

The fifteen browse species were selected after an initial field survey to evaluate the utilization of multipurpose tree and shrub forages as livestock feed in Western, Nyanza and Rift Valley provinces of Kenya. The leaf browses were harvested by hand clipping leaves from five branches on twenty mature trees in Kakamega, Baringo and East and West Pokot districts of Kenya in the dry season. The sampling sites were Malava, Chemeron Field Station of Egerton University, Kapenguria and Tangulbay, respectively. The forage species were as follows: Maerua angolensis, Acacia brevispica, Acacia mellifera, Acacia tortilis, Acacia hockii, Acacia elatior, Acacia nilotica, Acacia senegal, Acacia abyssinica, Balanites aegyptiaca, Grewia bicolor, Bridelia micrantha, Albizia amara, Albizia coriaria and Zizyphus mucronata. Only the leaves and leaf petioles were harvested and to mimick the parts browsed by goats.

Experimental procedures

The leaves were collected in gunny bags and dried in a shade for 6 days. The leaf browse was then milled through a 2.0mm screen for in-vivo digestibility, and a sub sample taken and milled further through 1.0mm screen for use in gas production trial, mineral assay and proximate analysis.

In-sacco degradation

Duplicate nylon bags (bag size, 80mmx140mm; pore size 45µm) containing 5g of milled dry sample were weighed and then incubated in the rumen of two fistulated Friesian steers 23 months old and weighing 540kg. The bags were then withdrawn after 3, 6, 12, 24, 48, 72 and 96 hours. The zero hour was obtained by soaking the bags in a water bath maintained at 39^oC for 1 hour. After the incubation period, the bags were withdrawn then hand washed under running tap water until the water coming out of the bags was clear. The washed bags and contents were then dried for 48 hours at 60^oC in a draught oven to determine DM disappearance. The disappearance values were fitted in the equation of McDonald (1981):

Y=a+b (1-e^-ct)

where a,b and c are degradation constants.

In-vitro gas production

The gas production technique of Menke and Steingass (1988) as described by Abdulrazak and Fujihara (1999) was used in the in-vitro gas production assessment. The net gas volumes data was then fitted in the equation of Ørskov and McDonald (1979):

G = a + b (1 - e^{-c t})

where:

G = the volume of gas produced (ml) at time t,
a = the gas production from the immediately soluble fraction (ml),
b = the gas production from the insoluble but degradable fraction (ml),
a + b = the potential gas production (ml),
c = the rate constant of gas production (fraction/h)

OMD48= organic matter digestibility at 48 hours.   

In-vitro organic matter digestibility calculated from the equation: OMD (%) = 18.53 + 0. 9239 gas production (at 48hrs) + 0.0540 CP (Menke and Steingass 1988).

Chemical analysis

The proximate composition including dry matter (DM), organic matter (OM), and total nitrogen (N) were determined following standard methods (AOAC 1990) and CP was calculated as N x 6.25. Neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL) were determined by the method of Van Soest et al (1991). Phenolics were extracted using 70% aqueous acetone and total extractable phenolics (TEPH) determined using Folin Ciocalteu procedures described by Makkar (2000). The TEPH concentration was calculated using the regression equation of tannic acid standard. Total extractable tannins (TET) were estimated indirectly after being absorbed to insoluble polyvinyl pyrrolidine (PVP) and the concentration calculated by subtracting the TEPH remaining after PVP treatment from the TEPH. Macro -elements calcium (Ca), phosphorus (P), magnesium (Mg), sodium (Na), sulphur (S) and micro-elements iron (Fe), copper (Cu), zinc (Zn), cobalt (Co), selenium (Se), molybdenum (Mo) and manganese (Mn) were analysed using atomic absorption spectrophotometer.

Results and discussion 

The results of the chemical analysis (Table 1.) of the test browses showed modest to high nutrient composition, indicating their potential for feeding ruminants.

The relatively high CP range (112 to 321 gkg^-1DM) of Acacia abyssinica, Acacia mellifera, Acacia brevispica, Acacia senegal, Zizyphus mucronata, Grewia bicolor, Albizia coriaria, Albizia amara and Maerua angolensis  browses show the potential contribution as protein feed resources for ruminants, especially browsing goats. This has been demonstrated in other tree legume browse in various studies (Ebong 1995, Abdulrazak et al 1997, Ben Salem et al 1997, Ondiek et al 1999, Abdulrazak et al 2000, Ondiek et al 2000, Abdulrazak et al 2001, Adjorlolo et al 2001, Nantoume et al 2001). Most of the reported parameters agree with the results of Abdulrazak et al (2000) who worked with acacia species. They reported high total extractable condensed tannins (100-480mgkg^-1DM) and total extractable phenolics (104-512mgkg^-1DM) for Acacia tortilis, Acacia seyal and Acacia nilotica that are very commonly used in the arid and semi arid areas of Kenya as livestock browse. The current study found both Maerua angolensis and Balanites aegyptiaca to be low in total extractable tannins 3 and 3gkg^-1DM and 114 and 152gkg^-1 DM in total extractable phenolics, respectively. The highest TEPH and TET were found in Acacia nilotica and Acacia hockii being 264, 267 gkg^-1DM and 244, 243 gkg^-1DM, respectively. Elseed et al (2002) indicated also similar levels of nutrients for some species. The Southern African browses reported by Dube et al (2001), using different mineral assays showed that Acacia nilotica, Acacia tortilis, Acacia senegal and Acacia albida had phenolic contents of 298, 107, 47 and 113gkg^-1DM, respectively. Elseed et al (2002) in a study of Sudanese browses reported variations between the early and late dry season with some nutrients (OM, NDF, ADF) being higher in the late dry season whereas CP, minerals, and digestibility of OM, N, In-vitro OMD and estimated energy showing higher values in the early dry season. They found Zizyphus spina-christi, Balanites aegyptiaca, Acacia tortilis and Acacia mellifera to be potentially valuable for dry season feeding and as protein and energy supplements. In the current study the materials were harvested after the rains and this could have had an effect on the nutritional composition and these compare favorably with those of Osuga et al (2006).

The macro and micro element composition of the forages is shown in table 2.

Generally the ash levels in acacia leaves of between 5 and 10% show that mineral contents in the forages are either deficient or moderately adequate (Sawe et al 1998). Fujihara et al (1992), Fujihara et al (1995) and Serra et al (1995) reported their work on minerals in various forages in dry and wet seasons. Fujihara et al (1992) found that the forages had on average 24µgkg^-1DM of Se while the Cu and Zn levels ranged between 7.6-24.3 and 11.4-50.6mg/kgDM, respectively. While Se was lower than the requirements (200µg/kgDM) for ruminants, the Cu and Zn were adequate for sheep rather than goats, indicating that goats need a higher level of these elements. The macro and micro-elements in diets selected by sheep reported by Serra et al (1995) indicated that the macro mineral levels (%) as follows: Ca (0.51), K (0.93), Mg (0.19), Na (0.44), and P (0.27) and micro minerals (mgkg^-1DM): Cu (13.5), Fe (510.9), Mn (43.8), and Zn (29.5). These values vary with those found in the current study, especially with Ca, Mg, P, Fe, Mn and Cu which were generally lower. However, the value for Na was similar to that reported.

The mineral content of the tree browses varies from moderate to high (Abdulrazak et al 2000). Although the P and Ca showed variability, the acacia species reported were rich in the micro-elements Mn, Mo, Zn, Co, Cu, Fe and Se showing that animals may consume adequate amounts and may only require specific supplementation. The current study reports the highest mineral levels for the macro elements Ca, P and Mg at 28, 3.2 and 8.7 gkg^-1DM and lowest levels at 7, 0.8 and 0.4 gkg^-1DM, respectively. Generally, the major minerals except sodium, were within the range of values previously reported (McDowell 1985). The values are adequate to meet the requirement for growth. The micro-element content in the current study is consistent with other reports (Topps 1992, Norton 1994, Ramirez and Ledezma-Torres 1997, Sawe et al 1998, Khanal and Subba 2001). In most studies reported, Na was generally low (Sawe et al 1998, Abdulrazak et al 2000, Khanal and Subba 2001). These agree with the results of the current study. Kendall et al (2001) reported the performance of sintered soluble glass Cu, Co and Se bolus that sustained adequate levels of the three trace elements in blood of sheep. For all the treated sheep the Co, Cu and Se in blood serum and liver increased compared to the non treated sheep, indicating that the sintered soluble glass Cu, Co and Se boluses could supplement these minerals for sheep.

The in-vivo degradation characteristics of the forage DM varied widely among the 15 forage species. The DM degradation characteristics exhibited a wide variation in the A and B portions and the fractional degradation ‘c’ rates in the species (Table 3).

Acacia hockii had the highest proportion of the ‘B’ fraction (97.7% DM) followed by G.bicolor (84.4% DM) at degradation rates ‘c’ of 0.0187 and 0.0116, respectively; while Albizia amara was the least degradable with a low ‘A’ value (21.6%) and the lowest ‘B’ fraction (14.9% DM) with an equally slow fractional degradation rate ‘c’ of 0.0168. The DM degradation of most of the forages improved from 24 to 48 hours, showing that they require more time to effectively degrade. The degradation at 48hrs shows Zizyphus mucronata was highest followed by Maerua angolensis at 90.7% and 88.6%, respectively. With these degradation potentials, the two species exhibited a reversed fractional out flow rates at k=0.05, these being higher for Maerua angolensis (78.9%) compared to Zizyphus mucronata (62.9%). This is desirable for the forages as the higher the degradability of the potentially degradable dry matter content the better the nutrient supply to the host animal. The two of the highly degradable forages Maerua angolensis and Zizyphus mucronata the DM is rapidly degraded initially for the former than the latter. These variations have been reported for tropical browses (Salawu et al 1999, Melaku et al 2003). These variations arise due to the phonological stage of development at harvest, (Salawu et al 1999) and nutrient composition of the various parts of the forage used (Melaku et al 2003). Therefore, the forages at 48hr degradation, could be categorized into three classes of low potential (29.9-50.2%), Albizia amara, Acacia abyssinica, Bridelia micrantha and Grewia bicolor; medium potential (50.3-70.5%), where only Acacia elatior fitted; and those that were observed to have high potential (70.6-90.7%) as Acacia brevispica, Acacia hockii, Albizia coriaria, Acacia tortilis, Acacia nilotica, Balanites aegyptiaca, Acacia mellifera, Acacia senegal, Maerua angolensis and Zizyphus mucronata. This latter group of forages could greatly contribute to goat and ruminant feed in general, and since they are also high in crude protein, they are potential protein supplements.

The gas production method of estimating nutritive value of feeds has been used to assess the rumen fermentation of the browses. The total gas production (ml/200mgDM) at 48hrs shown in table 4 indicate variations in the forage degradability and digestibility potential, with Maerua angolensis (52.2) and Zizyphus mucronata (45.7) being the highest and second highest, while Albizia amara (17.1) was the lowest.

These resulted to an estimated OMD at 48hrs of 73.9% and 68.5% and 35.2%, respectively. This shows that these browses are potentially degradable and can contribute to the nutrition of goats. However, they can be categorized as lowly degradable (35.2%-48.1%) for Bridelia micrantha, Acacia nilotica, Albizia amara, and Albizia coriaria; medium potential (48.2%-61.1%) for Acacia senegal, Balanites aegyptiaca, Acacia mellifera, Acacia brevispica, Acacia hockii and Acacia tortilis while the others were highly degradable (62.4%-73.9%) which included Acacia brevispica, Grewia bicolor, Acacia elatior, Zizyphus mucronata and Maerua angolensis.  The least gas production was obtained from Albizia amara, being 17.1ml/200mg. Presence of phenolic compounds could have contributed towards the low gas production shown by the forages under study, especially Albizia amara and Bridelia micrantha. These also had the lowest OMD values, being respectively 35.2% and 36.5%. As the presence of high levels of polyphenolic compounds in the forage could restrict preference and intakes of the leaf forages, it is possible that this attribute could contribute to the potentially low in-vivo DM degradation as well as gas production.

These assessments indicate that the forages are appreciably rich in protein, highly degraded and fermented in the rumen and contain low to moderate polyphenolic components and, therefore, could benefit ruminants in improving their protein nutrition especially when the availability of quality forages is low. Considering all parameters measured, the two outstanding forages are Maerua angolensis and Zizyphus mucronata which ranked first and second and this shows their potential for ruminant feed.

Conclusions

• The fifteen multipurpose tree and shrub species are abundant in Kenya. They were ranked on CP, total minerals, TEPH, TET, 48hr in-vitro and in-vivo degradation and OMD (%). They were ranked in order of increasing nutritive value into three categories of five species as follows: low (Bridelia micrantha< Albizia amara< Acacia hockii< Acacia nilotica< Acacia tortilis); medium (Acacia abyssinica< Grewia bicolor< Albizia coriaria< Acacia elatior) and high (Balanites aegyptiaca< Acacia mellifera< Acacia senegal< Zizyphus mucronata< Maerua angolensis).

  
  

• The leaf browses of the high potential group are suitable supplements and the best two, Maerua angolensis and Zizyphus mucronata, warrant further studies in feeding trials.

Acknowledgement 

The authors are grateful to the African Academy of Sciences for funding, Tatton Demonstration Farm for facilities and technical support from N K Kibitok, E K Shakala and J Museti.

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Received 3 December 2008; Accepted 20 November 2009; Published 7 February 2010

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