Chemical composition and its relationship to in vitro dry matter digestibility of several tannin-containing trees and shrub leaves

 

A Kamalak, J M P Filho*, O Canbolat**, Y Gurbuz, O Ozay and C O Ozkan

 

Kahramanmaras Sutcu Imam University, Faculty of Agriculture, Department of Animal Nutrition, Kahrmanmaras, Turkey.
^* Departamento de Medicina Veterinaria, Caixa Postal 64, Patos - PB, Brazil
^**Bursa Uludag University, Faculty of Agriculture, Department of Animal Nutrition, Bursa, Turkey.
akamalak@ksu.edu.tr

Abstract

 

The nutritive values of leaves from a shrub and 5 trees, Glycrrhiza glabra L, Arbutus andrachne, Carpinus betilus, Juniperus communis, Quercus libari L and Pistacia lentiscus L were evaluated based on their chemical composition and in vitro dry matter digestibility (IVDMD).

 

Crude protein (CP) content ranged from 5.74 to 12.6% with Glycrrhiza glabra L showing the highest value. Cell wall contents were high in all the leaves. The total condensed tannin content ranged from 4.34 to 20.3% with Juniperus communis and Carpinus betilus having the highest value.  The IVDMD values ranged from 41.7 to 52.8%. The NDF, ADF, ADL, TCT and SCT contents of leaves were negatively related, and CP positively related, with IVDMD.

 

It was concluded that Glycrrhiza glabra L and Quercus libari L may have a potential nutritive value for ruminant animals.

 

Key Words:  Composition, digestibility, leaves, tannins

Introduction

 

Trees and shrubs have been used for generations as multipurpose resources in many parts of the world (Smith 1992). Tree leaves are an important component of the diets of goats and sheep (Holechek 1984; Papachristou and Nastis 1996) and play an important role in the 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 often restricted by defending or deterring mechanisms related to high tannin content (Provenza 1995).

 

Although tree and shrub leaves are an important source of forage for small ruminants in most parts of Turkey during the critical periods of year when quality and quantity of pasture herbages are limited, there is little information on the nutritive value of tree and shrub leaves. The aim of the present work was to determine the chemical composition including condensed tannin content and in vitro digestibility of leaves of some tree and shrub leaves widely used for small ruminant animals in Turkey.

Materials and Methods

 

Forage samples

 

Leaves from 1 shrub and 5 trees, Glycrrhiza glabra L, Arbutus andrachne, Carpinus betilus, Juniperus communis, Quercus libari L and Pistacia lentiscus L, were harvested in August (growing season), September (mid growing season) and October (end of growing season) in 2003 from a city called Kahramanmaraş, in the south of Turkey. Juniperus communis is the only evergreen plant used in this experiment.

 

The area is located at altitude of 630 m above sea level. The mean annual rainfall and temperature are 857 mm and 16.2 ^°C respectively. Leaves were hand harvested from at least 10 different trees, then pooled and oven dried at 60 ^°C for 48 h (Abdulrazak 2000).

 

Chemical analysis

 

Dry matter was determined by drying the samples at 105 ^°C overnight and ash by igniting the samples in a muffle furnace at 525 ^°C for 8 h. Nitrogen (N) content was measured by the Kheldal method (AOAC 1990). CP was calculated as N X 6.25. EE were determined by the method of AOAC (1990). NDF content of leave samples were determined by the method of Van Soest et al (1991).

 

ADF and ADL contents of leave samples were determined following the method of Van Soest (1963). TCT, SCT and bound condensed tannin (BCT) were determined by the butanol-HCL method (Makkar et al 1995). Mimosa tannin (MT; Hodgson, England) was used as an external standard. The concentration of condensed tannin in the leaves was converted to g MT equivalent/kg DM.

 

In vitro dry matter Digestibility (IVDMD)

 

0.5 g of dry forages samples were subjected to a 48 h digestion period with the McDougall's buffer/rumen fluid mixture in sealed plastic bottles followed by 48 h digestion with pepsin in weak acid (Tilley and Terry 1963).

 

All incubations were carried out in triplicate. Three blank tubes (without sample) were used in each run. Rumen fluid was obtained from two fistulated sheep fed twice daily with a diet containing alfalfa hay (60%) and concentrate (40%).

 

After 48 h digestion with pepsin in weak acid, the samples were filtered (Whatman No 4) by gravity and the residues  placed in porcelain crucibles for drying at 65 ^°C for 48 h. The dry residues were weighed and digestibility was calculated using the equation as follows:

 

IVDMD (%) = [(initial DM input - (Residue - Blank) / initial DM input)*100]

 

Statistical Analysis

 

One-way analysis of variance (ANOVA) was carried out to compare the chemical composition and IVDMD values with species as the main factor using the General Linear Model (GLM) of Statistica for Windows (Stastica 1993). Significance between individual means was identified using Tukey's multiple range test (Pearse and Hartley 1966). Mean differences were considered significant at P<0.05. Standard errors of means were calculated from the residual mean square in the analysis of variance. A simple correlation analysis was used to establish the relationship between chemical composition and IVDMD.

 

Results and Discussion

 

Generally there were considerable variations in chemical composition among the species (Table 1). The CP content of  Glycrrhiza glabra L was  higher than for the other species. Feeds containing less than 8 % crude protein can not provide the minimum ammonia levels required by rumen microorganisms to support optimum activity according to (Norton (2003), thus the leaves of Arbutus andrachne and Juniperus communis are likely to require protein supplementation when they are the only feed consumed by ruminant animals. 

There were wide variation between tree species in terms of condensed tanis (TCT, BCT and SCT) (Table 2).

 

The chemical composition of Pistacia lentiscus L was similar to that reported by Decandia et al (2000). The chemical composition of Carpinus betilus was similar to that of Carpinus orientalis Mill reported by Papachristou (1996). TCT content of Pistacia lentiscus L was lower than was reported by Decandia et al (2000) and Silanikove et al 1996). They found that TCT contents of Pistacia lentiscus L were 21.7%and 20.5% respectively. The TCT content of Quercus libari L was similar to that of Quercus semecarpifolia reported by Singh et al (1998). With the exception of Quercus libari, the levels of total condensed tannins was above the range ( 60-100 g kg DM) that is considered to depress intake and growth (Barry and Duncan 1984). Supplementation of polyethylene glycol (PEG) might be a means of reducing the detrimental effect of the tannins, since  Pritchard et al (1998) showed that feeding of PEG to sheep eating mulga (Acacia aneura) leaves markedly increased feed intake, weight gain and wool growth.

 

There was a positive correlation (r= 0.53, P<0.05) between IVDMD and CP content, however, the latter explained  only 28% of the variation in IVDMD. This result is consistent with findings of Seresinhe and Iben (2003).

Figure 1. Relationship between IVDMD and CP content of the leaves

 

The relationships between cell wall components and IVDMD (Figures 2, 3 and 4), although consistent with the findings of Seresinhe and Iben (2003) and Balogun et al (1998), indicate that the cell wall indices in the present group of samples were relatively poor predictors of the IVDMD. 

 

Figure 2. Relationship between IVDMD and NDF content	Figure 3. Relationship between IVDMD and ADF content	Figure 4. Relationship between IVDMD and ADL content

 

 

There were negative relationships between the tannin contents of the leaves and IVDMD (Figures 5 and 6), the SCT apparently being a better predictor of IVDMD than TCT. These findings are similar to those reported by Balogun et al (1998), Frutos et.al (2002) and Seresinhe and Iben (2003).

 

 

The mechanism of dietary effects of tannins in ruminant nutritikon may be understood by their ability to form complexes with proteins. Tannins may form a less digestible complex with dietary proteins and may bind and inhibit the endogenous protein, such as digestive enzymes (Kumar and Singh 1984). Tannins can also adversely affect the microbial and enzyme activities( Singleton 1981; Lohan et al 1983; Barry and Duncan 1984; Makkar et al 1989). In tree leaves, tannins are present in significant amounts in the NDF and ADF fractions, and the binding of the proteins to the cell wall seem to be a factor in decreasing digestibility (Reed et al 1990).

Conclusions

 

It is concluded that Glycrrhiza glabra L and Quercus libari L may have a moderate nutritive value for ruminant animals in view of their IVDMD values (52%); however, the high content of condensed tannins in Glycrrhiza glabra (12.7%) and the low crude protein in Quercus libario (8.9%) may be limiting factors under practical feeding conditions.

 

 

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