Anti-nutritional components in leaves of some indigenous oak species at different growth stages

M R Al-Masri and M Mardini*

International Center for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria
ascientific@aec.org.sy
* Department of Agriculture, AEC, PO Box 6091, Damascus, Syria

Abstract

Total phenols (TP), tannins (T) and condensed tannins (CT) were determined in leaves of four indigenous oak species (Quercus libani, Quercus coccifera, Quercus cerris var. pseudocerris and Quercus infectoria) at six different growth stages [vegetative re-growth (new shoots), vegetative, bloom, fruit setting, fruit maturity, dormant].

TP and T concentrations significantly (P < 0.05) decreased in harvested leaves at dormant stage in comparison with young leaves of the new shoots. The TP and T concentrations were significantly higher (P < 0.05) in leaves collected at the vegetative re-growth and fruit maturity stages compared with the other growth stages. The TP and T contents in harvested oak leaves at vegetative, bloom and fruit setting stages amounted to 123 and 85 g/kg DM, respectively. The concentrations of T in leaves varied significantly (P < 0.05) among the studied oak species and decreased in the following order: Q. infectoria > Q. cerris var pseudocerris > Q. coccifera > Q. libani. The concentrations of CT increased significantly (P < 0.05) in leaves of Q. cerris var pseudocerris  (51.6 g/kg DM) and significantly decreased in  leaves of Q. libani (0.9 g/kg DM) in comparison with the other two oak species (Q. infectoria and Q. coccifera) (9.2 g/kg DM). The results suggested that oak young leaves harvested at vegetative re-growth stage from the new shoots would be harmful to livestock compared with those harvested at other experimental growth stages. Harvested oak leaves at dormant stage had low contents of tannins which suggests that they have potential as ruminant feeds. Among oak species, leaves of Q. libani had the lowest phenolics and therefore could possibly be used as dietary supplement for grazing livestock; subject to the absence of any other antinutritional and toxic factors. Further investigations using life animal studies are necessary to evaluate the nutritional value of the experimental oak species.

Key words: forage trees, Quercus spp., ruminant feeds, tannins

Introduction

Tree and shrub leaves are an important component of small ruminant diets in many parts of the world and play an essential role in nutrition of grazing animals in areas where few or no alternatives are available (Meuret et al 1990). However, the use of tree and shrub leaves by herbivores is restricted by deterring components such as mechanisms related to high tannins when present in high concentration content (Rubanza et al 2003; Bakshi and Walhwa 2004). The phenolic compounds (particularly tannins) in some trees and shrubs have an ability to bind reversibly or irreversibly to proteins in feed, saliva and microbial cells (Bae et al 1993; Hagerman and Robbins 1993; Jones et al 1994) and to inhibit ruminant micro-organism activity (Tanner et al 1994; Molan et al 2001). High levels of tannins in leaves restrict the nutrient utilization and decrease voluntary feed intake, nutrient digestibility and nitrogen retention (Kumar and Vaithiyanathan 1990; Silanikova et al 1996). However, feeding of tree and shrub foliages could be an attractive strategy for reduction of ruminal methanogenesis in animals fed with low-quality forage diets and for improving their productivity (Delgado et al 2012). Hydrolysable tannins appear to decrease methane production to a greater extent than condensed tannins (Goal and Makkar 2012).  

Oak leaves and twigs are often grazed by ruminants or harvested for use as livestock feed during feed shortages (Singh et al 1996). Quercus species (Q. ilex, Q. glauca, Q. semecarpifolia and Q. serrata) have been reported to contain high levels of tannins including both condensed and hydrolysable tannins (Makkar et al 1991). The value of leaves of Quercus incana as feeds for ruminants is offset by their potentially negative effects on protein utilization, and the risk of toxicity when intake is high (Garg et al 1992).

The seasonal variation of forage composition results from physiological changes which occur in plants during their growth perioding seasons. However, species vary in their response to climatic and physiological changes (Dann and Low 1988), and these differences determine their practical value as forage shrubs. The nutritive quality of the forage and its content of anti-nutritional components are influenced by harvest time and maturity stage (Makkar et al 1988 and 1991; Yihalem et al 2005; Al-Masri and Mardini 2008; Nordheim-Viken and Volden 2009; Nordheim-Viken et al 2009; Foster et al 2012; Al-Masri 2013). There is limited information regarding the effect of plant species and growth stage on the anti-nutritional components of oak leaves to be used as a feed for ruminants.

Objectives

The objectives of the present study were:

•  To evaluate leaves of oak species (Q. libani, Q. coccifera, Q. cerris var. pseudocerris and Q. infectoria) harvested at different growth stages [vegetative re-growth (new shoots), vegetative, bloom, fruit setting, fruit maturity, dormant] in terms of their contents of  anti-nutritional components.

  
  

• To study the changes in total phenols, tannins and condensed tannins in oak leaves, as affected by plant species and growth stage.

Materials and Methods

Sampling of materials

Leaves from four oak species (Q. libani, Q. coccifera, Q. cerris var. pseudocerris and Q. infectoria) were hand harvested at six different growth stages [vegetative re-growth (new shoots), vegetative, bloom, fruit setting, fruit maturity, dormant (fallen leaves)] from Qastal Maaf mountain (35^o 49΄ N; 35^o 57΄ E) about 47 km north of Latakia, Syria. Leaves were randomly sampled from at least 8 plants per species. Leaves pooled to four samples (n = 4) per species, air dried at room temperature (20-25 ^oC) for one week, ground to pass through a 1-mm sieve and stored frozen at -20 ^oC in sealed nylon bags for later analyses.

Determination of phenolic components

Samples were analysed for total phenols (TP), tannins T and condensed tannins (CT) by spectrophotometric methods. Total phenols were quantified by Folin Cio-calteu reagent and tannins as the difference of phenolics before and after tannin-phenol removal from the extract using insoluble polyvinylpyrolidone (Makkar et al 1993). Condensed tannins were determined by the butanol-HCL method (Porter et al 1986). Total phenols and tannins were expressed as tannic acid equivalent and condensed tannins as leucocyanidin equivalent.

Statistical analyses

Results were subjected to a factorial analysis of variance (ANOVA) test, using a Statview-IV program (Abacus Concepts, Berkeley, CA, USA). The two main factors were: oak species (Q. libani, Q. coccifera, Q. cerris var. pseudocerris and Q. infectoria) and growth stage (vegetative re-growth, vegetative, bloom, fruit setting, fruit maturity and dormant). Means were separated using the Fisher’s least significant difference test at the 95% confidence level.

Results and Discussion

Phenolic constituents components in oak leaves appeared to be influenced significantly by plant species and growth stages (Table 1). The total phenols (TP) and tannins T contents in leaves harvested at vegetative re-growth  and fruit maturity stages were significantly higher (P < 0.05) than that at the other stages, whereas the TP and T in harvested leaves at dormant stage were significantly lower than at the other stages (Figure 1). The TP and T contents in harvested oak leaves at vegetative, bloom and fruit setting stages amounted in average to 123 and 85 g/kg DM, respectively. Makkar et al (1991) indicated that the content of total extractable phenols was higher in younger leaves of Quercus ilex Linn, Quercus semecarpifolia Sm and Quercus serrata Roxb, whereas in Quercus glauca Thunb the content was higher in the mature leaves. Al-Masri and Mardini (2008) showed that TP and T concentrations significantly (P < 0.05) increased in leaves of Sesbania aculeate and Kochia indica harvested at seed formation stage compared with vegetable and bloom stages. In both plant species, neutral-detergent fiber and acid-detergent fiber concentrations were positively correlated with TP and T.

Figure 1. Changes in total phenols, tannins and condensed tannins in leaves of oak species harvested at different growth stage

Values of total condensed tannins CT exceeding 50 g/kg DM could inhibit microbial activity and depress dry matter digestibility (Kumar and Vaithiyanathan 1990). Arhab et al (2006) reported that the date palm leaves have high TP (30 g tannic acid equivalent/kg DM) and CT (55 g leucocyanidin equivalent/kg DM), and these value were generally considered too low to affect nutrient digestibility in ruminants (Frutos et al 2002, Makkar 2003). The CT in leaves of oak species harvested at different growth stages ranged from 11 g/kg DM in the young leaves harvested from the shoots at the vegetative re-growth stage to 27 g/kg DM in harvested leaves at fruit setting stage. Makkar et al (1988) indicated that the TP content decreased whereas the level of CT increased with maturity of Q. incana leaves. Young leaves of Q. calliprinos had lower levels (42 g/kg DM) of CT than the mature leaves (60 g/kg DM) (Gilboa 1996). Makkar and Singh (1991) showed that total phenols, T and CT levels (118, 132 and 38 g/kg DM, respectively) were higher in fresh leaves of Q. incana than in fallen leaves (33, 41 and 13 g/kg DM, respectively), and the fallen leaves might replace straws in ruminant feeds. However, Makkar and Singh (1993) suggested that storage of mature oak (Quercus incana) leaves in the presence of 4% urea and high moisture could become a field method for inactivation of oak tannins.        

Figure 2. Changes in total phenols, tannins and condensed tannins in harvested oak leaves, as affected by species

The results of this study showed that the species had a significant effect on the TP, T and CT of the oak leaves (Fig. 2). The TP content of Q. cerris was significantly (P < 0.05) higher than the others whereas the TP of Q. libani was significantly lower than the others. The concentrations of T in leaves varied significantly (P < 0.05) among the studied oak species and decreased in the following order: Q. infectoria > Q. cerris var pseudocerris > Q. coccifera > Q. libani. The TP, T and CT concentrations in leaves of Quercus coccifera was comparable to those obtained by Khazaal et al (1994) for the same species (124, 114 and 14 g/kg DM, respectively). The levels of T in the experimental leaves of Q. libani were lower than in Quercus persica (73 g/kg DM) and Quercus infectoria (109 g/kg DM) harvested during the summer in the NW of Iran (Yousef Elahi and Rouzbehan 2008). Among oak species, leaves of Q. libani had significantly (P < 0.05) the lowest contents of T and CT and therefore appear to be suitable as dietary supplement for grazing livestock.

The concentrations of CT increased significantly (P < 0.05) in leaves of Q. cerris var pseudocerris  (51.6 g/kg DM) and significantly decreased in  leaves of Q. libani (0.9 g/kg DM) in comparison with the other two oak species (Q. infectoria and Q. coccifera) (9.2 g/kg DM). The CT content of forages in the range of 60-100 g/kg DM depresses intake and growth of animals (Barry et al 1984). Getachew et al (2002) reported that plant samples containing total phenols and tannin levels (g tannic acid equivalent/kg DM) up to 40 and 20, respectively, were not expected to precipitate protein or cause increases in gas production upon addition of PEG to the in vitro ruminal gas production method and, therefore, are not likely to adversely affect ruminant productivity.

Conclusions

Based on the aforementioned obtained results it is concluded that:

• The concentrations of tannins in leaves varied among the studied oak species and were in the following order: Q. infectoria > Q. cerris var pseudocerris > Q. coccifera > Q. libani.
  
  
• Total phenols and tannins concentrations significantly decreased in harvested leaves at dormant stage of all studied oak species in comparison with young leaves of the new shoots.
  
  
• Oak young leaves harvested at vegetative re-growth stage might be harmful to livestock than those harvested at other growth stages.
  
  
• The harvested oak leaves at dormant stage (fallen leaves) had low contents of phenolic components which suggests that they might have potential as feeds for ruminants.
  
  
• Leaves of Quercus libani had the lowest phenolic components and therefore appear to be suitable as dietary supplement for grazing livestock in areas where no alternatives are available.
  
  
• In vivo studies are needed to determine the nutritive value of the experimental oak species harvested at different stages of maturity.

Acknowledgements

The authors thank the Director General and Head of Agriculture Department, A.E.C. of Syria, for their encouragement and financial support.

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Received 31 July 2013; Accepted 28 August 2013; Published 4 September 2013

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