Potential nutritive value of some mediterranean shrub and tree leaves as emergency food for sheep in winter

A Karabulut, O Canbolat, C O Ozkan* and A Kamalak*

BursaUludag University, Faculty of Agriculture, Department of Animal Science Bursa, Turkey
*Kahramanmaras Sutcu Imam University, Faculty of Agriculture, Department of Animal Science, Kahramanmaras, Turkey
akamalak@ksu.edu.tr

Abstract

The potential nutritive values of two shrub species (Quercus coccifera and Arbutus andrachne) and four tree species (Cedrus libani, Juniperus communis, Pinus halepensis, and Olea Europaea) were evaluated by chemical composition and in vitro gas production techniques.

There were significant differences among species in terms of chemical composition. Crude protein (CP) contents ranged from 9.2 to 10.5 %. Neutral detergent fibre (NDF) and acid detergent fibre (ADF) contents varied with species in the range 34.0-50.6 % and 25.8-38.7% respectively. Condensed tannin (CT) contents ranged from 4.8 to 20.1%.

There were also significant differences among species in terms of gas production and estimated parameters. The polyethylene glycol (PEG) addition significantly increased the gas production and some estimated parameters of shrub and tree leaves. However species showed variable responses to PEG treatment. The PEG supplementation had no significant effect on the gas production rate (c). On the other hand the PEG supplementation significantly increased the gas production (a) from rapid degradable fraction, gas production (b) from slow degradable and potential gas production (a+b). Although the OMD values of tree and shrub leaves without PEG ranged from 58.9 to 70.5 % the OMD values of tree and shrub leaves with PEG ranged from 64.5 to 77.5 %. The ME content without PEG ranged from 8.8 to 10.6 MJ kg/DM whereas the ME content with PEG 9.6 to 11.6 MJ kg/DM. Cedrus libani except Olea europaea had the highest OMD values when incubated in the absence of PEG whereas Quercus coccifera and Olea europaea had the highest OMD values when incubated in the presence of PEG. Cedrus libani except for Pinus halepensis had the highest ME content when incubated in the absence of PEG whereas Olea europaea except for Quercus coccifera had the highest ME content when incubated in the presence of PEG. The improvement in gas production, organic matter digestibility (OMD) and metabolizable energy (ME) with PEG emphasizes the negative effect of tannins on digestibility.

Key Words: Digestibility, metabolizable energy, nutritive value, PEG, shrub, tree leaves

Introduction

Shrub and tree leaves are an important component of diets for goats, cattle, deer, game, 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). The presence of tannins and other phenolic compounds in a large number of nutritionally important shrubs and tree leaves hampers their utilization as animal feed (Tolera et al 1997). High levels of tannins in leaves restrict the nutrient utilization and decrease voluntary food intake, nutrient digestibility and N retention (Kumar and Vaithiyanathan 1990, Silanikove et al 1996b, 2001).

The leaves of the evergreen tree and shrub such as Quercus coccifera and Arbutus andrachne, Cedrus libani, Juniperus communis, Pinus halepensis, and Olea europaea are used as an emergency food by the goat and sheep in the Mediterranean area during the winter when few or no alternatives are available. However there is little information on their nutritive values. Chemical composition, in combination with in vitro digestibility and ME content can be considered useful indicators for preliminary evaluation of the potential nutritive value of previously uninvestigated shrub and tree leaves (Ammar et al 2005). Current chemical analytical techniques do not reflect the biological effects of tannin therefore the use of in vitro techniques has been proposed to supplement the chemical analysis (Nsahlai et al 1994). The gas production technique has proved to be efficient in determining the nutritive value of feeds containing anti-nutritive factors (Khazaal et al 1993; Siaw et al 1993).

The aim of this study was to screen browse shrub and tree leaves from six species native to the southern of Turkey to (1) determine the chemical composition and quantify level of condensed tannin, (2) assess the effect of tannin activity on feed digestibility and nutrient availability in vitro using a polyethylene glycol (PEG) tannin bio-assay.

Materials and Methods

Leave samples

Leaves from two shrub species (Quercus coccifera and Arbutus andrachne) four tree species (Cedrus libani, Juniperus communis, Pinus halepensis and Olea europaea) were harvested by hand from at least 10 different trees in two experimental plots in winter 2005 in the southern of Turkey. The leaves from each plot were dried at 60 ^oC using a forced air oven. Dried leave samples were ground to pass through 1 mm sieve for subsequent analysis. The area located at altitude of 630 m above sea level. The mean annual rainfall and temperature are 642.1 mm and 16.9 ^oC, respectively.

Chemical analysis

Dry matter (DM) was determined by drying the samples at 105 ^oC overnight and ash by igniting the samples in muffle furnace at 525 ^oC for 8 h. Nitrogen (N) content was measured by the Kjeldahl method (AOAC 1990). Crude protein was calculated as N X 6.25. Cell wall contents (NDF and ADF) of leaves were determined using the method described by Van Soest et al (1991). Total condensed tannin was determined by butanol-HCl method as described by Makkar et al (1995). All chemical analyses were carried out in duplicate.

In vitro gas production

In the absence and presence of PEG (1 g, MW, 6000; Sigma, UK), the leave samples (0.200 g DM) were incubated in vitro with rumen fluid in calibrated glass syringes of 100 ml following the procedures of Menke and Steingass (1988). The aim of PEG addition was to determine the adverse effect of CT on the gas production and estimated parameters. All incubations were carried out in triplicate. Rumen fluid was obtained from two fistulated sheep fed a daily ration of 800 g alfalfa hay and 250 g concentrates divided into two equal meals at 8:00 and 16:00 h daily. The sheep had free access to water throughout the experiment.

Readings of gas production were recorded before incubation 0, 3, 6, 12, 24, 48, 72 and 96 h after incubation. Total gas values were corrected for blank gas production. The in vitro gas production kinetics were estimated fitting cumulative gas production data to the model suggested by Orskov and McDonald (1979) using a computer package programme called Fig P (Bio-Soft, Cambridge, UK).

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

where

y = gas produced at time't',
a = the gas production from the quickly soluble fraction (ml),
b = the gas production from the slowly degradable fraction (ml),
c = the gas production rate constant for the slowly degradable fraction (b),
t = incubation time (hour).

The metabolizable energy (MJ/kg DM) content and OMD (%) of leaves were calculated using equations suggested by Menke et al (1979) as follows:

ME (MJ/kg DM) = 2.20 + 0.136 GP + 0.057 CP

OMD (%) = 14.88 + 0.889 GP + 0.45 CP + 0.0651XA

Where

GP: 24 h net gas production (ml/200 mg DM),
CP: Crude protein (%),
XA: Ash content (%).

Statistical analysis

Data on chemical composition was subjected to the one way of ANOVA using GLM of Statistica for windows (1993). Data on the in vitro gas production kinetics, OMD and ME contents of leaves were subjected to the two way of ANOVA using GLM of Statistica for windows (1993). Significance between individual means was identified using the 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.

Results and Discussion

Chemical compositions of Quercus coccifera, Arbutus andrachne, Cedrus libani, Juniperus communis, Pinus halepensis, and Olea europaea are given in Table 1.

There were no significant (P>0.05) differences among species in terms of CP. The CP contents ranged from 9.2 to 10.5 %. The NDF and ADF contents varied with species in the range 34.0 -50.6% and 25.8-38.7% respectively. The NDF and ADF contents of Quercus coccifera were significantly (P<0.001) higher than those of Cedrus libani, Juniperus communis, Pinus halepensis and Olea europaea. There was a wide variation among species in terms of CT. The CT contents of Cedrus libani and Pinus halepensis were significantly (P<0.001) higher than those of the other species.

Variation in chemical composition among species could be partly due to genotypic factors that control accumulation of foliage nutrients (Rubanza et al 2005). The CP, ADF and CT contents of Arbutus andrachne and Juniperus communis were considerably lower than those reported by Kamalak et al (2005). Although CP content of Quercus coccifera was considerably higher than that obtained by Kamalak et al (2004) ash content of Quercus coccifera was comparable with that found by Kamalak et al (2004). This may be due to differences in growth site.

Leaves from two shrub species (Quercus coccifera andArbutus andrachne) four tree species (Cedrus libani, Juniperus communis, Pinus halepensis, and Olea europaea) had low CP compared to Acacia species reported by Rubanza et al (2005). However El-Shatnawi and Mohawesh (2000) suggested that ewes require 7-9 % CP for maintenance and 10-12 % for lactation. It seems to be likely that the shrub and tree leaves studied in this experiment will meet the CP requirements of ewes for maintenance and lactation since the CP content of shrub and tree leaves studied in this experiment fell into these ranges. However it is well known that CT had a significant effect on CP digestibility (Kumar and Singh 1984). The shrub and tree leaves selected in this study had high CT contents. Therefore optimal utilization of CP in browsable leaves could be limited by high levels of condensed tannin (50 g/kg DM) due to tannin activity through the chemical binding with dietary nutrients. Tannins may form a less digestible complex with dietary proteins and may bind and inhibit action of the endogenous protein, such as digestive enzymes (Kumar and Singh 1984). Tannin can thus adversely affect the microbial and enzyme activities (Singleton 1981, Lohan et al 1983, Barry and Duncan 1984, and Makkar et al 1989, Silanikove et al 1994; 1996a). In tree leaves tannins are present in NDF and ADF in significant amounts which are tightly bound to the cell wall and cell protein and seem to cause decreasing digestibility (Reed et al 1990). However in ruminants, dietary condensed tannins (2-3%) have been shown to have beneficial effects because they reduce the protein degradation in the rumen by the formation of a protein-tannin complex (Barry 1987).

The in vitro gas production of shrub and tree leaves in absence and presence of PEG are given in Figure 1.

Gas production increased with increased incubation time. The PEG supplementation considerably increased the gas production of leaves at all incubation times. The increase in the gas production in the presence of PEG is possibly due to an increase in the available nutrients to rumen micro-organisms, especially carbohydrates and nitrogen. McSweeney et al (1999) showed that addition of PEG caused a significant and marked increase in the rate and extent of ammonia production. It was also shown that supplementation of PEG at a level of 25 or 50 g per day to goat fed lentiks leaves and concentrate markedly increased in vivo dry matter, organic matter and protein digestibility (McSweeney et al 1999)

The effect of species and PEG addition on the gas production kinetics, OMD and ME contents of leaves are given in Table 2.

There are significant (P<0.001) differences among species in terms of gas production kinetics obtained with or without PEG supplementation. PEG supplementation significantly improved the gas production kinetics except for the gas production rate. On the other hand the PEG supplementation significantly (P<0.001) increased the gas production (a) from rapid degradable fraction, gas production (b) from slow degradable and potential gas production (a+b).

The effect of species and PEG addition on OMD and ME contents of leaves are given in Table 3. Addition of PEG resulted in higher (P<0.001) OMD and ME content, with variable responses among species.

Although the OMD values of tree and shrub leaves without PEG ranged from 58.9 to 70.5 % the OMD values of tree and shrub leaves with PEG ranged from 64.5 to 77.5 %. The ME content without PEG ranged from 8.8 to 10.6 MJ kg/DM whereas the ME content with PEG 9.6 to 11.6 MJ kg/DM. Cedrus libani except Olea europaea had the highest OMD values when incubated in the absence of PEG whereas Quercus coccifera and Olea europaea had the highest OMD values when incubated in the presence of PEG. Cedrus libani except for Pinus halepensis had the highest ME content when incubated in the absence of PEG whereas Olea europaea except for Quercus coccifera had the highest ME content when incubated in the presence of PEG.

Responses in OMD and ME due to supplementation of PEG in vitro were influenced (P<0.001) by species, PEG treatment, and interaction of species and PEG treatment. Juniperus communis had (P<0.001) the lowest OMD (58.9 %) and ME content (9.6 MJ/kg DM) in the absence of PEG compared to the other species. Quercus coccifera, Arbutus andrachne and Olea europaea had the highest OMD and ME increment due to PEG treatment. Cedrus libani had the lowest increment of OMD and ME content.

The increase in gas production, OMD and ME with PEG emphasizes the negative effect of tannins on digestibility. PEG, a non-nutritive synthetic polymer, has a high affinity to tannins and makes tannins inert by forming tannin PEG complexes (Makkar et al 1995). PEG also can also liberate protein from the preformed tannin-protein complexes (Barry et al 1986). Some studies clearly showed that PEG supplementation increased the gas production and volatile fatty acid production (Getachew et al 2001, Getachew et al 2002, Seresinhe and Iben 2003). The adverse effects of tannin on digestibility of Acacia spp. and Dichrostachhys spp. have been demonstrated by Makkar et al (1995) and Getachew et al (2000). However leaves of shrub and tree leaves did not give the same response for PEG addition, possibly due to differences in chemical composition of tannins, to variation in tannin anti nutritive activity between foliage species, to the nature of tannin and chemical structure (Dalzell and Kerven 1998), degree of polymerization (Schofield et al 2001).

Current findings on the effect of PEG on improved digestibility and ME are considerably lower than those of acacia species obtained by Rubanza et al (2005). The effect of PEG also depends on the level of proteins in diet. The higher the level of proteins the lesser is the effect of PEG (Makkar and Becker 1996). The level of CP in the foliage of Mediterranean bushes is often lower than 10% on dry matter basis (Leclerc 1984) with decreasing trend from spring up to the following autumn.

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