Assessment of seven under-utilized grain legume foliages as feed resources for ruminants

F T Ajayi, S R Akande, A A Adegbite and B Idowu

Institute of Agricultural Research and Training, Obafemi, Awolowo University, Moor Plantation, Ibadan, Nigeria
ajayiajay@yahoo.com

Abstract

Seven under-utilized grain legumes foliages and soybean foliage were evaluated for their nutrient composition, anti-nutrient contents, organic matter digestibility, short chain fatty acid and metabolizable energy levels in order to ascertain their relevance in livestock nutrition. In-vitro gas productions of the ground samples of the legumes foliage were determined every three hours until 24 hour.  Total gas (ml/200mg DM) at 24 hour was estimated for each of the legumes.

The analysis of nutrient contents (g/100g DM) showed  that crude protein ranged from 15.6 to 23.5g/100 g DM; Neutral detergent fibre was between 38.2 and 48.2g/100g DM while ether extract ranged from 1.0 to 2.3g/100g DM. Tannin content was between 1.8 and 6.5 g/100g DM while phytic acid was between 17.6 and 24.6 (mg/g).  Trypsin inhibitor ranged from 17.3 to 27.5 Tiu/mg protein. The legumes were high in metabolizable energy (8.20 – 11.7 MJ/kg DM), organic matter digestibility (56.0 – 78.0%) and short chain fatty acids (0.8 – 1.17 mmol).

The highest volume of gas, Y, was observed in Lablab. The value of gas production from insoluble fraction, b ranged from 14 to 33 ml/g DM. The lowest rate of gas fermentation, c value was observed in Pigeon pea. It is concluded that these legumes foliages could be used as supplement in livestock diets except Pigeon pea which had the least degradation characteristics.

Key words: Anti-nutrients, degradation characteristics, gas fermentation, under-utilized grain legume foliages

Introduction

Ruminant livestock productivity in many African countries is low in terms of milk and carcass yield compared to what is obtained in developed countries.  The feed resources that are abundant to provide the bulk of ruminant feeds are biomass from grasslands and crop residues which cannot sustain the animals’ productivity especially during the dry season.  This poor nutrition leads to economic losses to the farmers because of loss in weight and condition of animals, poor reproductive performance and increase rates of mortality especially the young animals. Improved feeding systems based on supplementation of grass with forage legume (Babayemi et al 2006) will enhance milk yield and meat production.

There is the need to supplement legumes in the diets of livestock species in order to enhance their productivity.  Under-utilized grain legume foliages like African Yam beans (Sphenostylis stenocarpa Hochst ex A. Rich) Harms, Lima beans (Phaseolus lunatus) sword beans Canavalia gladiata, pigeon pea (Cajanu cajan), Bambara groundnut (Vigna subterranean), Jack beans (Canavalia ensiformis), Dolichos Lablab (Lablab purpureus) could be explored to provide relevance in livestock feeding.  These legumes are classified as minor grain legumes because they are under exploited and are indigenous legumes usually cultivated in association with arable crops like cassava, yam, etc.

These legumes are cultivated in central and Western Africa especially Cameroon, Ghana, Nigeria for the seeds and at the end of the planting season; the foliages are set on fire.  They are being neglected in most Nigeria homes for consumption because of the long hours of cooking and tedious manual removal of skin coats. (Adeparusi 2001).  A large biomass of these legume foliages is  produced post harvest annually.

This study is designed to compare the nutritive value, metabolizable energy, organic matter digestibility and degradation constants of these under-exploited grain legume foliages.

Materials and methods

Two hundred milligrams of ground samples of the foliage of Bambara groundnut, Lima beans, Jack beans, sword beans, pigeon pea, African yam beans, lablab and soybeans were separately weighed into 100ml calibrated syringes with pistons lubricated with Vaseline. A buffered mineral solution was prepared consisting of (NaHCO₃ + Na₂HPO₄ + NaCI + MgSO₄. 7H₂O +CaCI₂ 2H₂O (1:4, v/v) and stirred at 39⁰C under continuous flushing with carbondioxide (CO₂).  Rumen fluid was collected from two female West African Dwarf (WAD) does that were previously fed concentrate  consisting of 20% maize, 20% corn bran, 25% wheat offal, 20% Palm kernel cake, 10% groundnut cake 4% oyster shell, 0.5% common salt, 0.25% fish meal and 0.25% grower premix.  In addition, foliages of Gliricidia sepium and Panicum maximum were fed to the animals for two days prior to the collection of rumen liquor.

The liquor was collected into a pre-warmed thermos flask and was later filtered through three layers of cheese cloth and flushed with carbondioxide. About 30ml of buffered rumen fluid was taken into syringes containing the feeds.  The syringes were placed in an incubator at 39⁰C. Gas production rates were recorded at 3, 6, 9, 12, 15, 18, 21 and 24  hour of incubation and each syringe was gently swirled after reading.  At the end of 24 hours incubation, 4ml NaOH was added to the substrate in each syringe to determine the methane production.

Rates and extent of gas production were determined for each substrate from the linear equation:

Y = a + b (1 – e ^–ct)

described by Ǿrskov and McDonald (1979).
 

Where

Y = volume of gas produced at time‘t’,
a = intercept (gas produced from the soluble fraction),
b = Potential gas production (ml/g DM) from the insoluble fraction,
c = gas production rate constant (h^-1) for the insoluble fraction (b),
t = incubation time. 

The metabolizable energy (MJ/Kg DM) and organic matter digestibility (OMD%) were estimated from volume of gas produced after 24 hour of incubation (GP, ml/200mg DM) and the proportion of crude protein (CP, g/100g DM) as established by Menke and Steingass (1988):

OMD = 24.91 + 0.72222GP + 0.0815CP

ME = 2.2 + 0.1357GP + 0.0057CP + 0.0002859CP²

Short chain fatty acid (SCFA) values were calculated as described by Getachew et al (1999) using SCFA = 0.0239*GV – 0.0601 in the absence of PEG, where PEG = Polyethylene glycol and GV = Gas volume as described by Getachew et al (1999).

Chemical analysis

Ground samples of the underutilized legume foliages were analyzed for dry matter, ash, crude protein, fiber fractions and ether extract by the procedures of AOAC (1990). Acid detergent fiber, neutral detergent fibre and acid detergent lignin were determined according to procedures described by VanSoest et al (1991). Saponin, phytate and trypsin inhibitors were analyzed by methods of Okwu and Josiah (2006), Maga (1983) and Kakade et al (1969), respectively, while tannin and oxalates were determined by method of Beutler et al (1980).

Statistical analysis

Data were analyzed by the analysis of variance (ANOVA) techniques using the General Linear model procedures of  (1998). Treatment means were compared using the Duncan Multiple range test (Gomez and Gomez 1984).

Results 

Table 1 shows the proximate composition of the foliages.

The dry matter (DM) was between 42.6% in Sword beans and 52.5% in African yam beans. Crude protein (CP) ranged from 15.6% in Jack beans to 38.5% in Soybean. Ether extract (EE) was between 1.5% and 13.2% in Lima beans and Soybean respectively. The Neutral detergent fiber (NDF) ranged from 38.2% in Lima beans to 48.2% in Jack beans. Acid detergent fiber (ADF) values ranged from 14.3% in Soybean to 26.2% in Lablab. Acid detergent fiber (ADL) ranged from 3.3% in Soybean to 8.3% in African yam beans. Nitrogen free extract (NFE) mean values were between 8.5% and 18.1% in Pigeon pea and Lablab respectively.

The secondary metabolites of the foliages is shown in Table 2.

The tannic acid range from 2.85 g/100g in Pigeon pea to 6.5 g/100g in Lima beans. Phytate concentration was highest in Pigeon pea (24.6 g/100g) and lowest in Jack beans (13.2 g/100g). The mean value of trypsin inhibitor was between 17.3 and 27.5 Tiu/mg in Bambara groundnut and Soybean respectively. The saponin content was highest in Bambara groundnut (1.8 g/100g) and lowest in Soybean (1.0 g/100g). Oxalate content in the legumes ranged from 0.3 g/100g in Bambara groundnut to 0.8 g/100g in Lablab.

Table 3 shows the metabolizable energy (ME), organic matter digestibility (OMD) and short chain fatty acid (SCFA) of the foliages.

Highest ME was observed in Lablab (11.7 MJ/kg) while the mean values for soybean, African yam bean and pigeon pea foliages were similar (P>0.05). Similarly mean values for Bambara groundnut, Jack beans, Sword beans and Lima bean foliages were comparable. Organic matter digestibility values differed significantly (P<0.05) among the legumes with  Lablab having the highest value. However, means of OMD observed for Soybean (71.8%) and Sword bean (72.5%) foliages were similar (P>0.05). The mean value of SCFA of the legumes were not significantly different (P>0.05) in soybean, pigeon pea and sword bean foliages.

The gas production characteristics of under-utilized grain legume foliages is shown on Table 4.

The volumes of gas produced in Jack bean and sword bean were the least. The highest volume of gas was in Lablab (31.0 ml), followed by soybean (22.0 ml). The potential gas production (ml/g DM) from insoluble fraction, b ranged between 14.0 ml/g DM in Lablab and 43.0 ml/g DM in Pigeon pea. The rate of gas productions also differed significantly among the legumes. Higher rates of gas production were observed in Soybean and Lablab (0.211 h^-1 and 0.159 h^-1 respectively). The lowest rate of gas production was observed in Pigeon pea (0.003 h^-1).

Discussion 

The crude protein contents of the under-utilized legume foliages in this study were higher than values obtained for Cassia rotundifolia, Lablab purpureus and Macroptilium atropurpureum (Siratro) which are forage legumes (Mupangwa et al 2000). Similarly, the crude protein contents of pigeon pea, African yam bean and lima bean foliages corresponds with the values obtained for Leucaena leucocephala and Gliricidia sepium   (Babayemi et al 2006), Ficus spp. (Bamikole et al 2003). Similarly, the NDF, ADF and ADL values corresponds with reported values (Babayemi et al 2006) for herbaceous and tree legumes.

The level of tannin which does not adversely affects digestibility in sheep and cattle is between 2% and 5% (Diagayete and Hugg 1981). Goats can tolerate about 9% dietary tannin (Nastis and Malechek 1981). The values of phytate (12.4 – 24.6 mg/g) obtained in this study were within the range of 82.0 mg to 292.9 mg/g for ruminant nutrition. Similarly, oxalate content obtained was also within the range of 0.33 to 2.06 mg/100g for ruminant nutrition (Onwuka 1996). These values show that some essential minerals such as Ca, Mg, Fe and Zn would be made available for animals from the forages. Saponin levels are usually low in foliages (Gestetner et al 1966). Saponin undergoes bacterial degradation in the rumen and so does not retard growth in ruminants.

Digestibility is synonymous to in-vitro gas production (Fievez et al 2005) such that the higher the volume of gas produced the higher the digestibility. The low volume of gas produced in Lima bean and Jack bean shows that these legume forages have low digestibility whereas Lablab, swordbean and soybean are high in digestibility. The under-utilized grain legume forages except Lablab and Soybean had high tannin contents. It is reported that feed that is high in tannin content has low digestibility because it reduces the population of fibre degrading bacteria in the rumen and hence low activity (McSweeney et al 1999). The values of gas production characteristics obtained in this study are higher than values reported (Babayemi and Bamikole 2006) for Tephrosia candida. The volume of gas produced, Y, and gas production from insoluble fraction, b obtained are comparable to values obtained for Stylosanthes guianensis, Lablab purpureus, Centrosema pubescens and Aeschynomene histrix (Ajayi and Babayemi 2008). However, the rate of gas production, c was low in the under-utilized legumes in this work compared to values reported for the herbaceous legumes (Ajayi and Babayemi 2008). The rate of gas production, c is synonymous to the rate at which degradation of substrates occurs in the rumen. Pigeon pea, Lima beans and Jack beans had low rates of gas production.

Conclusions 

• The under-utilized grain legume foliages possess high nutritive contents which made it possible to be used in the diets of ruminant livestock.

  
  

• The foliages of soybeans, sword beans, lablab and African yam beans are suitable to be used as supplements in grass or crop residue based diets for ruminants. 

  
  

• Foliages of Pigeon pea, Bambara groundnut, Lima beans and Jack beans, appear to be unsuitable for this purpose.

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Received 4 June 2009; Accepted 13 June 2009; Published 1 September 2009

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