Chemical composition and in vitro dry matter digestibility of leaves of Vitis vinifera

A Kamalak

Kahramanmaras Sutcu Imam University, Faculty of Agriculture, Department of Animal Nutrition, Kahrmanmaras, Turkey
akamalak@ksu.edu.tr

Abstract

The nutritive values of leaves from ten varieties of Vitis vinifera were evaluated based on their chemical composition and in vitro dry matter digestibility (DMD).

Crude protein (CP) content ranged from 7.9 to 11.2 % with Honüsü having the highest protein content. Neutral detergent fiber (NDF) and acid detergent fibre (ADF) ranged from 27.1 to 46.3 % and 17.9 to 39.4 %, respectively. Condensed tannin (CT) content of leaves ranged from 2.4 to 5.0 % with Besni and Kardinal having the highest CT content. The in vitro DMD values ranged from 59.8 to 75.3 %. The IVDMD was negatively correlated with cell wall contents (NDF, ADF) and CT contents. ADF, NDF and CT alone or in various combinations explained 39.6 - 63.5 % of the variation of in vitro DMD.

It was concluded that leaves of Sultani, Perlette and Honusu may have a high potential nutritive value for ruminant animals in terms of rumen and whole tract digestibility.

Key words: Chemical composition, condensed tannin, dry matter digestibility, Vitis vinifera

Introduction

Tree and shrub leaves have the potential for alleviating some of the feed shortages and nutritional deficiencies experienced in the lean periods on smallholder farms. Tree and shrub leaves are an important component of goat and sheep diets (Holecheck 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 al1990). 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).

Grapes are widely grown in the Mediterranean basin, producing considerable quantities of by-products. Traditionally, this residue is grazed by sheep or goats after the harvest (Magnier 1991). Approximately 525,000 ha of area in Turkey were used for grape production in 2001 (DIE 2001). Although leaves of Vitis vinifera are an important source of forage for ruminants in Turkey during the critical period when quality and quantity of pasture herbages are limited there is no information about the nutritive value of leaves of Vitis vinifera varieties. Therefore, the aim of this study was to evaluate the potential nutritive value of leaves of ten Vitis vinifera varieties grown in Turkey based on their chemical composition, and in vitro dry matter digestibility.

Materials and Methods

Forage samples

Leaves of 10 different varieties of Vitis vinifera after harvest were hand collected from three replicate plots established in the experimental field in the city of Kahramanmaras in Turkey in September, 2004. The area is located at an altitude of 630 m above sea level. The mean annual rainfall and temperature are 857.5 mm and 16.2 ^ºC, respectively. The leaves were shade-dried and representative dry samples from each plot were taken to the laboratory and milled in a hammer mill through a 1 mm sieve for chemical analysis and in vitro DMD.

Chemical analysis

Dry matter (DM) was determined by drying the samples at 105 ^ºC overnight and ash by igniting the samples in a muffle furnace at 525 ^ºC for 8 h. Content of nitrogen (N) was measured by the Kheldal method (AOAC 1990). The CP was calculated as N X 6.25. Contents of neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined by the method of Van Soest et al (1991). Condensed tannin (TCT) was determined by the butanol-HCL method (Makkar et al 1995). Mimosa tannin (MT; Hodgson, England) was used as an external standard.

In vitro dry matter digestibility (IVDMD)

Dry forage samples (0.5g) were subjected to a 48 h digestion period with McDougall's buffer/rumen fluid mixture in sealed plastics 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 ^ºC for 48 h. The dry residues were weighed and digestibility was calculated using the equation

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 in vitro DMD values with varieties as the main factor using the General Linear Model (GLM) procedure (Stastica 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. Simple correlation and regression analyses were used to establish the relationship between chemical composition and in vitro DMD.

Results and Discussion

Generally there were considerable variations in chemical compositions between the varieties (Table 1). The CP content of leaves of Honusu was significantly (P<0.001) higher than for the other varieties. The CP contents of leaves of Kabarcık, Yalova Incisiand Bozcaada Cavusu were lower than that required by micro-organisms in the rumen to support optimum activity (Norton 2003). The leaves were higher in CP than those reported by Rebole (1994) and Romero et al (2000) for samples of grape vines (branches and leaves). In this study the samples did not contain any branches.

Table 1. Chemical composition (%) and in vitro dry matter digestibility (DMD) of leaves from 10 different varieties of Vitis vinifera
Varieties	DM	CP	ADF	NDF	Ash	CT	DMD
Kabarcık	39.4^de	9.3^b	39.4^g	46.3^f	11.2^a	3.7^b	67.0^bcd
Kardinal	36.43^bcd	10.4^de	30.2^f	39.3^e	13.2^abc	5.0^d	59.8^a
Sultani	27.9^a	9.9^cd	17.9^a	27.1^a	11.9^ab	3.4^b	72.2^ef
Yalova Incisi	37.9^cd	9.5^bc	27.5^e	35.5^d	12.3^ab	4.1^c	66.3^bcd
Perlette	31.6^ab	10.5^e	22.0^b	30.9^b	12.3^ab	2.4^a	75.3^g
Honüsü	32.7^ab	11.2^f	22.9^bc	31.3^b	14.8^c	4.2^c	73.4^fg
Bocaada cavusu	43.9^e	7.9^a	24.7^cd	33.0^bc	11.2^a	3.4^b	68.4^cde
Ata sarısı	33.9^bc	10.4^de	22.4^bc	30.9^b	13.2^abc	3.7^b	70.3^def
Besni	33.2^bc	9.8b^c	30.3^f	38.0^e	13.1^abc	5.0^d	63.5^a
Hatun parmagı	33.4^bc	10.4^de	27.2^de	35.1^cd	17.3^d	4.4^c	65.6^bc
Sig.	***	***	***	***	***	***	***
SEM	1.007	0.107	0.516	0.468	0.482	0.081	0.808
DM: Dry matter, CP: Crude protein, ADF: Acid detergent fiber, NDF: Neutral detergent fiber, CT: Condensed tannin, DMD: Dry matter digestibility,*** P<0.001, Means within the same column without superscript in common are different. Sig: Significance level, SEM: Standard error of mean

ADF content varied with varieties in the range 17.9-39.4%. The ADF content of leaves of Kabarcık was significantly (P<0.001) higher than the other varieties. Ash content of leaves ranged from 11.2 to 17.3 %. The NDF and ADF contents of leaves were comparable to those reported by Romero et al (2000). The geographic area or the season in which samples are collected influence the chemical composition of vine byproducts (Alvira et al 1983).

TCT content of leaves varied with varieties in the range 2.4-5.0 % (Table 1). The TCT contents of Kardinal and Besni were significantly (P<0.001) higher than the other varieties. Tannin contents of forages in the range of 60-100 g kg DM (6 to 10%) depress intake and growth (Barry and Duncan 1984). The tannin contents of leaves obtained in this experiment fell towards the lower end of this range. Therefore it is unlikely that CT in leaves of Vitis vinifera may have a detrimental effect on the intake and growth of ruminants. The CT values of the leaves were comparable to those obtained by Rebole (1994) and Romero et al (2000). They found that CT of leaves of Vitis vinifera was approximately 5 % of DM. The in vitro DMD of leaves of Sultani, Perlette and Honusu were significantly (P<0.001) higher than those for Kabarcık, Kardinal, Yalova Incisi, Besni and Hatun Parmagı, possibly due to low level of NDF, ADF and CT (Table 1).

There were significant (P<0.001) negative correlations between in vitro DMD and cell wall contents (ADF and NDF) (Table 2). This result is consistent with findings of Balogun et al (1998), Seresinhe and Iben (2003) and Ammar et al (2004).

Table 2. Correlation coefficients between chemical constituents and in vitro dry matter digestibility
	DM	Ash	CP	ADF	NDF	CT
Ash	-0.323^NS
CP	-0.699***	0.588***
ADF	0.498***	-0.150^NS	-0.229^NS
NDF	0.490***	-0.162^NS	0.224^NS	0.999***
CT	0.054^NS	0.401*	0.128^NS	0.391*	0.377*
DMD	-0.372*	-0.075^NS	0.179^NS	-0.635***	-0.629***	-0.688***
DM: Dry matter, CP: Crude protein, ADF: Acid detergent fiber, NDF: Neutral detergent fiber, CT: Condensed tannin, DMD: Dry matter digestibility, NS: Non-significant (P>0.05), * P<0.001, P<0.05

There was also a significant negative correlation between in vitro DMD and CT. This result is consistent with findings of Balogun et al (1998), Frutos et al (2002) and Seresinhe and Iben (2003).

In tree leaves, tannins are present in the NDF and ADF fractions and are tightly bound to the cell wall and cell protein and seem to be involved in decreasing digestibility (Reed et al 1990). They may form a less digestible complex with dietary proteins and may bind and inhibit the endogenous proteins, such as digestive enzymes (Kumar and Singh 1984); tannin can adversely affect the microbial and enzyme activities (Singleton 1981; Lohan et al 1983; Barry and Duncan 1984; Makkar et al 1995).

In ruminants, dietary condensed tannins (2-3% in DM) have been shown to impart beneficial effects because they reduce the wasteful protein degradation in the rumen by the formation of a protein-tannin complex (Barry 1987). Species with moderate levels of tannins having higher proportion of escape protein than those without tannins have been reported (Albrecht and Broderick 1990). Regression equations showed that chemical constituents of leaves, alone or in various combinations, were well correlated with in vitro DMD (Table 3).

Table 3. Prediction of in vitro dry matter digestibility from chemical constituents
Y	Equation and factors	R²	P	MSE
DMD	y = 81.6 -0.383*DM	13.8	NS	4.463
	y = 70.6 – 0.185*Ash	0.6	NS	4.793
	y = 58.5 + 0.97*CP	3.2	NS	4.729
	y = 81.6 – 0.506*ADF	40.3	***	3.715
	y = 87.7 – 0.561*NDF	39.6	***	3.737
	y = 86.1 – 0.463CT	47.4	***	3.487
	y = 90.9 – 0.344ADF – 0.350CT	63.1	***	2.972
	y = 95.3 – 0.384NDF – 0.354CT	63.3	***	2.965
DM: Dry matter, CP: Crude protein, ADF: Acid detergent fiber, NDF: Neutral detergent fiber, CT: Condensed tannin, DMD: Dry matter digestibility, NS: Non-significant (P>0.05), *** P<0.001 MSE: Error Mean Square

ADF, NDF and CT alone or in various combinations explained 39.6 - 63.3 % of the variation of in vitro DMD. The inclusion of CT in the equation together with ADF or NDF improved the precision of the prediction. These parameters in combination explained 63.1 - 63.3 % of the variation of in vitro DMD. This result is in agreement with finding of Fonseca et al (1998) who found that NDF explained 61 % of the variation of organic matter digestibility of some roughages.

Conclusions

Variety had a significant effect on the chemical composition and in vitro DMD of grape vine leaves
Sultani, Perlette and Honusu varieties had relatively high protein content and in vitro DMD and thus have the potential to be good quality forages for ruminant animals during the critical periods.

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