Evaluation of tropical tree leaves as ruminant feedstuff based on cell contents, cell wall fractions and polyphenolic compounds

D V Reddy and N Elanchezhian

Rajiv Gandhi College of Veterinary and Animal Sciences, Kurumbapet, Puducherry 605009, India
dv.duvvuru@gmail.com

Abstract

Seven tropical tree leaves were analysed for proximate principles, cell wall fractions on organic matter basis, protein content of NDF and ADF, .non-fibre carbohydrates, calcium and phosphorus, total phenolics, total tannins, condensed tannins and B3 slowly rumen degraded protein content. These trees were Acacia auriculiformis (Australian wattle), cashewnut (Anacardium occidentale), Gliricidia sepium, jack (Artocarpus heterophyllus), Sesbania grandiflora, subabul (Leucaena leucocephala) and yellow gold mohur or copper-pod tree (Peltophorum ferrugineum). Our objective was to use certain discerning chemical constituents (protein, phenolics, ADL, B3) to evaluate these tree leaves for their potential as ruminant feedstuff.

The differences between NDF and NDFom (Table 2) reflected the ash content from fibre in NDF analysis, which ranges from 0.71 in case of subabul to 2.93% for acacia leaves. Similarly ash from fibre in ADF analysis ranged between 1.47 in case of jack and sesbania leaves and 2.27% in cashewnut leaves. NFC was calculated in two ways as 100 minus NDF, protein, lipids and ash in a feedstuff with or without NDF corrected for protein. The NFC values derived with NDF corrected for protein are appropriate.

Total phenolics of acacia, cashewnut, gliricidia, jack, sesbania, subabul and yellow gold mohur, respectively, were 13.4, 20.3, 5.6, 15.6, 9.4, 11.3 and 12.5%. Sesbania, subabul and gliricidia were kept in best category in view of their higher protein, lower lignin and phenolics, while acacia, jack and yellow gold mohur in the next best category. Cashewnut leaves were kept in the last category in view of relatively lower protein and higher lignin and phenolics, which were responsible for the low nutritive value of them in goats. However, considering the beneficial effect of condensed tannins in protecting protein from rumen degradation, cashewnut or other leaves may be incorporated at appropriate level in the ruminant diet.   

Keywords: ash-free, ADF, B3, carbohydrate, condensed tannins, NDF, tannin

Introduction

Trees of several species could provide palatable and nutritious fodder during drought and scarcity periods by lopping their branches (Reddy 2006). There are many advantages of the forages from multi-purpose tree crops (Devendra 1992). The leaf fodder of some trees is almost as nutritious as that of the leguminous fodder crops. However, presence of antinutritional factors (ANF), especially tannins limits their use as animal feed.

Based on their structures and properties, tannins are distributed into two major classes-hydrolysable tannins (HT) and condensed tannins. Condensed tannins (CT) are hydrolytically cleaved to anthocyanidins and related compounds and are more correctly called proanthocyanidins or proflavanoids. Tannins are hydrosoluble polymers that form complexes with proteins, starch, cellulose and several minerals (Makkar 2003a). These complexes are broken under conditions of high acidity (pH < 3.5) or high alkalinity (pH > 7.5) (Jones and Mangan 1977). Hence condensed tannins may be used as organic protectant of protein from rumen degradation. Anthelmintic effects are also reported.

Carbohydrates are defined as fibre carbohydrates (equal to neutral detergent fibre, NDF) and non-fibre carbohydrates. Rumen microbes and animals utilize the different fractions of protein, non-ibre carbohydrate and structural (fibre) carbohydrate fractions differently and their estimation in the feedstuffs elucidates more information about their availability (Sniffen et al 1992). Inadequacies in the nitrogen free extract of the Weende analysis have been addressed by development of methods to quantify the nonstructural carbohydrates (NSC), which are mainly starches and sugars. The NSC and non-fibre carbohydrates (NFC) or neutral detergent soluble carbohydrates (NDSC), which are calculated by difference, are distinct fractions (NRC 2001). NDSC include some fibre carbohydrates such as pectins, β-glucans and fructans.

In the present study seven very common trees of Puducherry area are selected and an attempt has been made to find out the fibre components, non-fibre components and various phenolic fractions of their leaves for assessing their potential in feeding ruminant animals.

Materials and methods

Sample collection and processing

Trees such as Acacia auriculiformis (Australian wattle), cashewnut (Anacardium occidentale), Gliricidia sepium, jack (Artocarpus heterophyllus), Sesbania grandiflora, subabul (Leucaena leucocephala) and yellow gold mohur or copper-pod tree (Peltophorum ferrugineum) are chosen for the study. Fresh tree leaves were hand plucked in the month of April 2007 and brought to the laboratory. The tree leaves were sun-dried with due care separately and ground to fine mesh. Sun drying was preferred because oven drying of feeds that contain proanthocyanidins, even at temperatures below 60ºC, increased NDF, fibre bound nitrogen and lignin (Reed et al 1984).

Chemical analyses

Dry matter, total ash, crude protein (CP), ether extract (EE), crude fibre (CF), acid insoluble ash (AIA) (AOAC 1995) and calcium and phosphorus (Talapatra et al 1940) were analysed. Tree leaves were also analysed for neutral detergent fibre (NDF) without using a–amylase and sodium sulphite (Van Soest et al 1991) and acid detergent fibre (ADF), acid detergent lignin (ADL) and silica (Goering and Van Soest 1970). The NDF was expressed exclusive of residual ash (referred henceforth as NDFom) and ADF was corrected by the ash content of the ADL residue (ADFom), as recommended by Van Soest (2006), because of varying soil contamination in forages and feeds. The neutral detergent insoluble crude protein (NDICP) was derived by determining CP of the insoluble residue of the NDF extraction. The acid detergent insoluble crude protein (ADICP) was determined as the CP associated with the insoluble residue of an ADF extraction. Nitrogen free extract (NFE) and .non-fibre carbohydrate (NFC) fraction that is soluble in neutral detergent (Neutral detergent soluble carbohydrates, NDSC) were calculated.

Extraction and determination of total phenolics and tannins

Leaf samples (200 mg) were extracted with ultrasonicator (Cell Disrupter Ultrasonic Probe, Model 1000L) at 4°C in 10 ml aqueous acetone solution (acetone/water: 7/3 v/v). After centrifugation (3000 x g at 4°C for 20 min), the supernatants (total phenolics extract) were analysed for phenolic components (total phenolics, non-tannin phenolics, total tannin phenolics and condensed tannins) as described by Makkar (2003b) using Spectronic^R Genesys 2 Spectrophotometer.

Contents of total phenolics was analysed using the Folin – Ciocalteu’s reagent (Sisco Research Laboratories Pvt Ltd, Mumbai, India) based on tannic acid standard (Qualigens fine chemicals, GlaxoSmithKline Pharmaceuticals Ltd, Mumbai, India). Total phenolics consist of simple phenolic compounds or non-tannin phenolics and pure tannins or total tannin phenolics. Polyvinyl polypyrrolidone (PVPP; Sigma – Aldrich) has the property to bind tannins but not the simple phenolics. Two ml distilled (triple glass) water and 2 ml total phenolics extract were added to the test tube containing 200 mg PVPP and vortexed twice and filtered through Whatman No 1 filter paper. The filtrate was used to estimate non-tannin phenolics, which was subtracted from total phenolics to obtain total tannins. The concentration of total phenolics and total tannins were expressed as tannic acid equivalent.

Condensed tannin

Three ml n-butanol – HCl (95:5 v/v) and 0.1 ml ferric ammonium sulphate (1%) were added to the test tube containing 0.5 ml phenolics extract. The test tube was closed with a glass marble and heated in a boiling water bath for 60 min. The absorbance of the red anthocyanidin products (i.e., condensed tannin) was measured at 550 nm and condensed tannin was expressed as leucocyanidin equivalent.  

All parameters had been analysed in duplicate and the average values were presented in the respective tables.

Results and discussion 

Chemical composition

The CP content of the leaves of Acacia auriculiformis, cashewnut, Gliricidia sepium, jack, Sesbania grandiflora, subabul and yellow gold mohur, are reported in Table 1.

Tree leaves may be ranked CP content wise as follows: Sesbania grandiflora, Gliricidia sepium, subabul, Acacia auriculiformis, jack, yellow gold mohur and cashewnut leaves. The proximate principles, AIA, Ca and P of tree leaves except gliricidia are comparable with the data obtained from an earlier project (Anon 2007). The tree leaves are good sources of calcium and have the following calcium: phosphorus ratios: subabul (7.47), Sesbania grandiflora (6.72), Gliricidia sepium (4.95), yellow gold mohur (3.00), acacia (1.72). jack (1.72) and cashewnut (1.48).    

The ADL content (Table 2) of Sesbania grandiflora, subabul, jack and Gliricidia sepium ranged from 4.31 to 7.86 % while yellow gold mohur, Acacia auriculiformis and cashewnut leaves contained higher levels (13.47 to 15.23).

Silica levels also followed about the same trend. Perusal of cell wall fractions (Table 2), proximate principles and others (Table 1) recorded in the present study show these are broadly comparable with the values reported by several workers (Senani et al 1997; Radhakrishnaiah et al 1997; Panda et al 1988; Das and Ghosh 2001; Van et al 2005; Reddy 2006; Dey et al 2006; Anon 2007). Variation in the chemical composition of tree leaves, just as it reported for other feeds, is usually observed due to the climate and soil on which the trees grow, collection and processing of the samples for analysis. Differences in NDF, ADF and ADL, could be due to species genotypic differences in factors that control fibre accumulation in the plant, and stage of growth. Fibre contents increase with advanced foliage maturity due to lignification (Minson 1990).

Ash (%) from fibre in NDF analysis and in ADF analysis, respectively, were 2.93 and 1.83 for acacia, 2.48 and 2.27 for cashewnut, 1.29 and 1.73 for gliricidia, 2.03 and 1.47 for jack, 1.13 and 1.47 for sesbania, 0.71 and 2.10 for subabul and 1.36 and 1.83 for yellow gold mohur leaves. In view of this great variation in the ash content, the NDF and ADF should be expressed on an ash-free basis in tree foliage, as advocated by Van Soest (2006) for rice straw.

No data are available on Acacia auriculiformis, cashew nut and yellow gold mohur, except the proximate and fibre analysis work that has been done in our laboratory (Anon 2007). The average chemical composition of Acacia species may be used for comparison (Madibela et al 2004): CP 18.65, NDF 46.13, ADF 27.84, ADL 13.92, Ca 2.17 and P 0.12%. The average NDICP was 7.53% and it was 40.38 as percent of CP. The ADF, ADL and NDICP of Acacia auriculiformis of the present study are similar while CP and NDF are lower compared to the average of Acacia spp.

NDICP, ADICP and non-fibre carbohydrates

The CP content insoluble in neutral detergent solution (NDICP) was 11.53, 10.56, 8.50, 7.75, 7.03, 6.56 and 4.88%, respectively, for sesbania, gliricidia, subabul, acacia, yellow gold mohur, jack and cashew leaves (Table 2). In yellow gold mohur, acacia, cahewnut and jack leaves half and more than half of total CP was in NDF while gliricidia, subabul and sesbania leaves had only 43.3, 38.6 and 33.1% of CP in NDF. With reference to ADICP, all tree leaves studied contained 15.5 to 19.0% of CP in the ADF except sesbania, which had 10.4%. The published reports revealed that NDICP and ADICP as % CP for subabul leaves were 19.08 and 11.22 (Bhadauria et al 2002), 28.63 and 18.61 (Singh et al 2002), 33.28 and 14.27 (Mondal and Walli 2003) and 33.7 and 10.7 (Kumaresan 2004). The observed values in our study for subabul were 38.64 and 16.18 as NDICP and ADICP as %CP. Kumaresan (2004) reported NDICP and ADICP as %CP 30.2 and 7.4 for Sesbania grandiflora leaves and 34.8 and 9.0 for gliricidia leaves while 33.06 and 10.4 for sesbania and 43.31 and 18.21 for gliricidia were obtained in the present study.

The calculated difference between NDICP and ADICP (Table 2) is christened as B3 while the ADICP is called as C in the CNCPS (Cornell net carbohydrate and protein system) fractionation of protein in feedstuffs (Sniffen et al 1992). In the parlance of CNCPS, B3 is slowly (rumen) degraded true protein and C is undegraded true protein. The B3 values for Acacia auriculiformis, cashewnut, Gliricidia sepium, jack, Sesbania grandiflora, subabul and yellow gold mohur leaves, respectively, were 4.81, 3.13, 6.12, 4.56, 7.90, 4.94 and 4.81%.  Among the tree leaves studied, Sesbania grandiflora had highest amount of slowly rumen-degraded protein followed by gliricidia, subabul, acacia, yellow gold mohur, jack and cashew. The intestinal digestibility coefficients for B3 (0.80) and C (0.00) are not always as indicated. This is particularly true for the assumption that fraction C always has a digestibility of 0.00. Several studies indicate that variable amounts of ADICP are digested in the small intestine (NRC 2001; McNiven et al 2002).

The calculation of .non-fibre carbohydrates (NFC or NDSC) and ratio between NFC: NDF (Table 2) throws light on the suitability of these tree leaves as sole diets when available in plenty as well as supplementary feeds in ruminant feeding. NFC was calculated in two ways as 100 minus NDF, protein, lipids and ash in a feedstuff with or without NDF corrected for protein. The NFC values derived with NDF corrected for protein are appropriate. The NFC (with protein corrected fibre) contents varied from 33.1 (subabul), 33.4 (gliricidia), 37.8 (yellow gold mohur), 44.2 (cashewnut), 46.8 (acacia), 47.5 (sesbania) to 53.4 (jack) % of dry matter in different tree leaves. Kumaresan (2004) reported 33.6% for subabul and 36.1% for gliricidia, which are in agreement with the present values and the NFC of sesbania was 24.7, which is much less compared to that obtained in the present study. The NFC values for two pools of microbes exist in the CNCPS and microbial growth is a function of carbohydrate (NDF and NFC) availability at the given availability of appropriate nitrogen sources (Russell et al 1992). Nitrogen must be supplied as NPN or free AA and peptides. Fermenters of NDF can only utilize ammonia while fermenters of NFC also need slowly degraded protein to meet their peptide requirement, which is provided by B3 fraction.

The optimal concentration of .non-fibre carbohydrates (NFC) is important in ruminant diets to avoid acidosis and other metabolic problems. Diets with excess NFC can cause ruminal upsets and health problems (Nocek 1997). From the NRC (2001) recommended maximum NFC and minimum NDF concentrations for lactating cow diets, the calculated ratio between NFC and NDF varies from 1.76 to 1.01. The ratios for the tree leaves under study (Table 2) are 2.01 for sesbania, 1.67 for jack, 1.15 for acacia, 0.91 for cashewnut, 0.65 for yellow gold mohur, 0.61 for gliricidia and 0.57 for subabul leaves.  

Polyphenolics compounds

The leaves of cashewnut were found to be most tanniniferous as they contained highest total phenolics, total tannin phenolics and condensed tannins (Table 3).

The tree leaves may be ranked from the highest to the lowest as per the content of total phenolics as follows: cashewnut, jack, Acacia auriculiformis, yellow gold mohur, subabul, Sesbania grandiflora and Gliricidia sepium. The same trend was observed in case of total tannin phenolics as well. Phenolics wise the tree leaves may be grouped as cashewnut with highest; jack; sesbania, subabul, yellow gold mohur and acacia; gliricidia with lowest phenolics. The available values in the literature for Gliricidia sepium and subabul (Mlambo and Makkar 2005) are 3.5 and 2.6% for total phenolics, 2.2 and 1.5% for tannin phenolics, 1.0 and 0.87% for condensed tannins while for jack leaves the respective values are 24.2, 23.0 and 19.1% (Dey et al 2006). Van et al (2005) reported the tannin content for jack leaves as 5.1%, stems 1.5% and the stems and leaves together 4.2%. Total tannin and condensed tannin levels for subabul foliage were 5.5 and 2.9% and 4.0 and 3.4% were for jack leaves (Ally and Kunjukutty 2003). Sesbania grandiflora leaves had 1.9% total tannins (Panda et al 1988). The values obtained in the present study for subabul, gliricidia and sesbania are higher than those reported while the data for jack leaves are intermediate with Dey et al (2006) data being higher and Van et al (2005) and Ally and Kunjukutty (2003) data lower.

No literature is available for Acacia auriculiformis, yellow gold mohur and cashewnut leaves for these phenolic fractions. Browse tree leaves from six species of Acacia were analysed and the range (%) for different chemical constituents was as follows: CP 14.5-22.9, NDF 22.2-50.5, ADF 13.4-28.6, ADL 5.5-14.5, total phenolics 9.9-28.1 and total tannins 8.4-25.6 (Rubanza et al 2005). The observed values in the present study are with in this range. Tannin composition in plants is known to depend on soil fertility, environmental conditions, maturity of the leaves, processing of the sample for laboratory analysis and the analytical method employed (Makkar 2003b). The wide variance in the polyphenolic compounds of the present study may be attributed to the reasons listed by Makkar (2003b).

Chemical composition and nutritive value  

Tree leaves rich in total phenolics (Table 3) such as cashewnut, Acacia auriculiformis and yellow gold mohur had also higher ADL (Table 2) with the exception to this was jack tree leaves. Conspicuously, feeding of cashewnut leaves that had highest phenolics (20.3% total phenolics) and highest ADL (15.2%) resulted in depression in DM intake (1.4% body weight), digestibility of DM (37%) and CP (44.1%) and nutritive value (DCP 4.2% and TDN 41.0%) in goats (Anon 2007). The limited feed intake and lowered digestibility of nutrients in goats fed on cashewnut tree leaves could be due to very high levels of tannins and the consequent astringent sensation in the mouth of the animal, which corroborated the findings of Provenza and Roop (2001). This sensation results in a negative feedback that influence the animal to reduce consumption of tannin-rich feeds. Higher level of lignin in cashewnut leaves might have increased retention time in the rumen, and consequently intake would be limited and it is in agreement with the findings for Acacia cyanophylla (Bensalem et al 1997). Deleterious effects of phenolics and tannins include inhibition of digestive enzymes, toxic effects on rumen microbes (Osuji and Odenyo1997) and toxic effects on intestinal mucosa (Mangan 1988).

Bhatta et al (1999) indicated the formation of tannin-protein complex even at room temperature without processing, which helped its protection from rumen degradation. Studies of Dey et al (2006) revealed that supplementation of condensed tannins at 1-2% level significantly reduced the in vitro nitrogen degradability of groundnut cake. However, results are to be viewed with caution in view of the observations of Vitti et al (2004) casting a doubt on the generalization that small amounts of CT (2-4%) produce beneficial effects or that high levels (>5%) are harmful. Rather it appears that tannins in some plants are either particularly beneficial or detrimental.  

The data generated for the commonly fed tree foliages related to their CP, protein content of NDF and ADF and the calculated B3 fraction, NDFom, ADFom, and the .non-fibre carbohydrates along with the phenolic fractions, among the other chemical constituents, help to evaluate the tree leaves as ruminant feedstuff for sustainable and ecofriendly animal production. Tree leaves could be considered promising and interesting sources for incorporation into ruminant diets.

Acknowledgements 

The authors wish to thank the Dean, Rajiv Gandhi College of Veterinary and Animal Sciences, Puducherry, India for providing necessary facilities to carry out the experiment.

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Received 5 January 2008; Accepted 5 March 2008; Published 1 May 2008

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