Technical Note
Digestibility and voluntary intake of
vine leaves (
Vitis vinifera
L.) by sheep
M.J. Romero
a, J. Madrid
b, F. HernaÂndez
b,*, J.J. CeroÂn
caCentro de CapacitacioÂn y ExperimentacioÂn Agraria, ConsejerõÂa de Agricultura, Ctra. de Aguas Nuevas, km. 6.7, 02071 Albacete, Spain bDepartamento de ProduccioÂn Animal, Universidad de Murcia, Campus de Espinardo, 30071 Murcia, Spain
cDepartamento de PatologõÂa Animal, Universidad de Murcia, Campus de Espinardo, 30071 Murcia, Spain
Received 25 July 1999; accepted 11 April 2000
Abstract
Twelve castrated adult male (623 kg body weight) Manchego sheep were used in a digestion trial. Diets consisted of vine leaves or vetch-oat hay alone, and vetch-oat hay and vine leaves in a ratio of 1:1. Voluntary intake of vine by-products by eight females Manchego sheep was also measured. The CP level was greater in vetch-oat hay (73g kgÿ1DM) than vine leaves
(68 g kgÿ1DM) and the vine leaves had a higher level of neutral-detergent insoluble crude protein (NDF-CP, 38 g kgÿ1DM) than vetch-oat hay (17 g kgÿ1DM). NDF was less in vine leaves (319 g kgÿ1DM) than in vetch-oat hay (566 g kgÿ1DM).
However, the lignin content of cell walls in vine leaves (146 g kgÿ1NDF) was higher than hay (127 g kgÿ1NDF). The content
of condensed tannins of the vine leaves (50 g kgÿ1DM) was 10 times higher than that of the vetch-oat hay. DMD and OMD of
vine leaves was 42.2 and 47.2%, respectively. Apparent digestibility of CP in vine leaves was negative (ÿ25.8%) and was lower (P<0.001) than CP digestibility of vetch-oat hay (48.9%). Digestibilities of NDF and ADF of vine leaves were 3.8 and ÿ0.6%, respectively. These values were lower (P<0.001) than those obtained for vetch-oat hay (53.9 and 54.7%, respectively). DM and DOM intake of vine leaves was 1010.7 and 415.3 g per day, respectively. With the exception of urea, there were no differences (P>0.05) between sheep fed leaves and those fed vetch-oat hay in measured plasma metabolites. These results suggest that the low digestibility of the vine leaves is due to several factors, such as the high level of condensed tannin content and low protein digestibility.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Vine leaves; Vetch-oat hay; Condensed tannins; Digestibility; Voluntary intake; Blood metabolites
1. Introduction
In Mediterranean countries, sheep nutrition is based on natural grazing and supplementary feeding con-sisting mainly of roughage, by-products and concen-trates. The roughage usually used is hay mainly
consisting of annual sown legumes and small grain cereals such as common vetch-oats. Caballero and GarcõÂa (1996) concluded that common vetch is the legume used by most farmers (90%) and oat is the main species used as a companion crop (50%) in areas of Central Spain.
Grapes are widely grown in the Mediterranean basin, producing considerable quantities of by-pro-ducts. Grapevines consist of branches and leaves from annual pruning of vineyards. Traditionally, this resi-due is grazed by sheep or goats after the harvest
*Corresponding author. Tel.:34-68-364745;
fax:34-68-364147.
E-mail address: nutri@fcu.um.es (F. HernaÂndez).
(Magnier, 1991).The most important feature of the by-product of grapes is their low energy value re¯ecting a high cell wall content and low digestibility of the cell wall fraction. This is associated with a high content of lignin and other antinutritional factors, such as tannins (Alvira et al., 1983).
Tannins, a naturally-occurring polyphenolic com-pound in vine by-products, are present either in hydro-lyzable or condensed forms (Butler, 1989). They form complexes with proteins, polysaccharides, amino acids, fatty acids and nucleic acids (Flores et al., 1994). Both the composition and the extent of poly-merization of tannins are important factors in deter-mining their ability to form such complexes. In addition, there is an inverse relationship between high tannin level in forage and palatability, digestibility and voluntary intake. In the present study, the digestibility and intake of vine tree leaves were measured when fed alone and in a mixed ration with vetch-oat hay, and the blood metabolic pro®le in sheep consuming vine leaves was examined.
2. Materials and methods
Vetch-oat (Vicia sativa L.±Avena sativa L.) hay harvested in mid May at early-seed and full-bloom stages for vetch and oat, respectively, was used. The botanical fractions of the hay were 65% of oat and 35% of vetch. Vine tree (Vitis viniferaL.) leaves from annual pruning (performed in October) after harvest were used. Stems were discarded leaving only the leaves as fresh feed.
Twelve castrated adult male (623 kg body weight) Manchego sheep were used in the digestion trial. A completely randomized design was used and the animals were assigned to three diets consisting of vine leaf or vetch-oat hay alone, and vetch-oat hay and vine leaf in a ratio of 1:1. The hay was cut into 2± 5 cm lengths. Animals were in individual digestibility cages. The digestibility trial lasted 21 days (14 days for acclimatization and 7 days for the experiment); feces were collected and daily intake controlled. Feed was offered at an intake level close to maintenance (40±45 g DM kgÿ1
LW0.75per day) as recommended by Van Es and Van Der Meer (1980).
In the voluntary intake trial, eight female Manchego sheep with an initial body weight of 463 kg were
used. Animals were kept in individual pens and fed with a ration consisting of vine leaves with barley grain-supplement at a level of 200 g DM per animal per day. The intake trial lasted 44 days (14 days for acclimatization and 30 days for the experiment), dur-ing that time daily intake was measured. Feeds were offered ad libitum daily to sheep in suf®cient quan-tities to enable them to refuse at least 200 g DM kgÿ1 DM of feed offered. The amount of feed offered was adjusted daily on the basis of the intake of the previous day to achieve the target refusal rate. Feed refusals were collected before feeding. In both trials sheep were fed once daily at 10:00 hours and had free access to water and a mineral block. All the animals used in the experiments were vaccinated and drenched.
Blood samples (10 ml) were taken from each sheep used in the digestibility and intake experiments. In addition, a control group fed with vetch-oat hay was used for the sheep intake trial. Blood was taken at 09:00 hours during the last 2 days of each experiment from the jugular vein by a syringe, and the plasma was separated and stored atÿ208C.
Feces were collected daily from each animal and dried in a forced air oven at 608C for 48 h and ground through a 1 mm screen. Daily fecal samples (20% of the total) together with a sample of the feed offered, were stored for subsequent analyses.
The feces and feed samples were analyzed for dry matter (DM), ash, crude protein (CP) and ether extract (EE) according to AOAC (1984) methods. To deter-mine cell components, neutral detergent ®ber (NDF), acid detergent ®ber (ADF) and permanganate lignin the methods proposed by Van Soest et al. (1991) were followed. Acid-detergent insoluble nitrogen (ADIN) and the neutral-detergent insoluble nitrogen (NDIN) were measured (Licitra et al., 1996), and these values were given in terms of crude protein (ADF-CP and NDF-CP, respectively).The vanillin±HCl (Broadhurst and Jones, 1978) method was used for determination of condensed tannins (TC).
(AST), alkaline phosphatase (ALP) and gamma glu-tamyltranspeptidase (GGT) were measured.
All data were subjected to one way analysis of variance (ANOVA) (Steel and Torrie, 1980). Differ-ences among means were tested using Duncan's new multiple range test.
3. Results and discussion
CP content of vine leaves was 68 g kgÿ1
(73 g kgÿ1 for hay). These values agree with the values reported by Rebole et al. (1988) for samples of grapevines (branches and leaves), but CP content of vine leaves is higher than those obtained by Rebole (1994) for vine branches, either fresh (60 g kgÿ1
) or ensiled (50 g kgÿ1
). The geographic area or the season in which it is collected in¯uence the chemical composi-tion of vine by-product (Alvira et al., 1983).
NDF and ADF levels were 319 and 254 g kgÿ1for vine leaf (566 and 364 g kgÿ1for hay). The proportion of lignin content of cell wall in the vine leaf (146g kgÿ1 NDF) was higher than in the hay (127g kgÿ1
NDF).The content of condensed tannins of the vine leaves (50 g kgÿ1
) was 10 times higher than that of the vetch-oat hay (5 g kgÿ1
). Similar values were found by Rebole (1994) for fresh vine branches. Digestibilities of vine leaves, vetch-oat hay and vine leaves/vetch-oat hay (1:1) diets are given in Table 1. DMD and OMD of vine leaves were lower
(P<0.001) than those of vetch-oat hay. According to these data, vine leaves could be considered low quality roughage (Ellis et al., 1988). However, DMD of vine leaves is higher than those obtained by Rebole et al. (1988) for ensiled grapevines, due to the fact that this by-product contains leaves and branches. CP apparent digestibility of vine leaves was negative (ÿ25.8%) and was lower (P<0.001) than the CP digestibility of vetch-oat hay (48.9%). This result may be due to several factors. Firstly, the vine leaves had a higher level of NDF-CP (38 g kgÿ1, a 56% of CP is bound to cell wall) than that of vetch-oat hay (17 g kgÿ1). Rebole et al. (1988) reported 4 g kgÿ1
for NDF-CP for grapevines, equivalent to 61.5% of CP bound to the cell wall, and they found that digestibility of CP in NDF was negative (ÿ16.4%). Licitra et al. (1996) indicated that the nitrogen associated with NDF is normally cell wall-bound protein, which includes the slowly degradable protein and the indigestible nitro-gen found in the acid-deternitro-gent residue. Secondly, it could be due to the presence of condensed tannins in vine leaf. These compounds form complexes with proteins and carbohydrates (Makkar et al., 1996), decreasing the available nitrogen and energy for rumen micro-organisms.
The low digestibilities of NDF and ADF of vine leaves might be due to the high content of lignin and tannin content in this by-product.
DM and DOM intake of vine leaves was 1010.7 and 415.3 g per day, respectively. The presence of tannin
Table 1
Apparent digestion coef®cients of vetch-oat hay and vine leaf
Item Vine leaf:vetch-oat hay S.E.M.d Pe
100:0 50:50 0:100 a,b,cMeans in the same row with different superscripts are signi®cantly different.
dStandard error of means.
in a forage has been assumed to affect voluntary intake (McLeod, 1974). However, in this trial intake pro-blems were not observed.
There were no differences between sheep fed with leaves and vetch-oat hay in the digestibility trials in any plasma metabolite, except urea (Table 2). In sheep fed with hay, the urea concentration (29.5 mg 100 mlÿ1) was higher (P<0.01) than in sheep fed with leaves (8.9 mg 100 mlÿ1
), which is most likely related to the limitation in protein digestibility in sheep fed vine leaves. Similar results were found by Silanikove et al. (1996) where urea concentration was higher in goats fed with tannin-rich leaves than when fed wheat straw.
In the intake trial more plasma metabolic para-meters showed signi®cant differences than in the digestibility trial. A possible explanation for these higher differences could be due to the experimental period in intake trials of vine leaves (44 days), which was higher than in the digestibility trial (21 days). Speci®cally, plasma urea nitrogen and total protein decreased (P<0.01), and creatinine increased (P<0.001). This effect, during consumption of leaves, could be explained by negative nitrogen balance. The increase of creatinine observed can be related with renal failure, but the level found in the present study fell within the normal range for sheep (Kaneko, 1989). No signi®cant changes in plasma enzymes AST and GGT were found. These enzymes are used to detect if
tannin-related hepatotoxicity occurred (Zhu and Filip-pish, 1992).
It is concluded that the low digestibility of the vine leaves might be due to factors such as the high levels of lignin and condensed tannins, and low protein digestibility. However, this by-product was accepted by sheep and toxic effect was not evidenced in this study.
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Blood metabolic pro®le of sheep fed vine leaves and vetch-oat hay (control)
Item Digestibility trials Voluntary intake trial
Vine leaves:vetch-oat hay Vine leaves Control S.E. Pe
100:0 50:50 0:100 S.E.M.d Pe
Urea (mg 100 mlÿ1) 8.9a 20.5b 29.5c 0.9 *** 7.6 33.2 0.9 ***
Creatinine (mg 100 mlÿ1) 0.9 0.9 0.8 0.0 NS 1.1 0.7 1.0 ***
Albumin (g 100 mlÿ1) 3.2 3.0 3.0 0.0 NS 2.8 2.8 0.0 NS
Protein (g 100 mlÿ1) 7.6 7.2 7.4 0.2 NS 6.5 7.3 0.1 **
Cholesterol (mg 100 mlÿ1) 63.7 62.0 70.5 3.6 NS 61.3 64.0 2.5 NS
Glucose (mg 100 mlÿ1) 78.5 80.9 77.7 3.0 NS 70.3 62.9 2.3 NS
AST (units lÿ1) 55.6 51.1 57.5 4.3 NS 69.5 57.5 4.6 NS
GGT (units lÿ1) 34.0 38.2 34.7 2.4 NS 34.5 36.0 1.1 NS
ALP (units lÿ1) 50.8 49.7 53.2 1.1 NS 75.1 52.5 5.4 NS a,b,cMeans in the same row with different superscripts are signi®cantly different.
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