Livestock Research for Rural Development 28 (8) 2016 Guide for preparation of papers LRRD Newsletter

Citation of this paper

In vitro rumen fermentation kinetics and nutritional evaluation of olive tree (Olea europaea L.) pruning residues as affected by cutting regimen

M R Al-Masri

Department of Agriculture, A E C S, P O Box 6091, Damascus, Syria
ascientific@aec.org.sy

Abstract

Nutritive values of the branches (stems with leaves) from Olea europaea trees cut at 25, 50, 75 or 100 cm distance from the tip (cutting length) were evaluated by determination of the microbial nitrogen (MN) and biomass (MBM) production after incubation with rumen fluid and 15N-tracer for 96 h in the absence or presence of polyethylene glycol (PEG, 6000). The characteristics of fermentation (initial gas produced from soluble fraction; a, gas production during incubation which produced from insoluble but fermentable fraction; b, potential gas production; a + b, fractional rate of gas production per hour; c) were assessed using an in vitro incubation technique with rumen fluid. Effective degradability (ED), partitioning factor (PF) and short chain fatty aids (SCFA) were also estimated in the experimental olive pruning branches.

There was a negative effect of cutting length on all the studied nutritive parameters and fermentation characteristics. The values of MN, MBM, ED, PF, SCFA, a + b and c declined with the increase in cutting length. The olive branches cut at 25 or 50 cm distance from the tip produced higher (P<0.05) amounts of MN (0.53 mg/g DM) than those cut at 75 and 100 cm lengths (0.30 mg/g DM). The values of ED, SCFA and PF, and the ratios of MN or MBM to effective degraded substrate were significantly higher (P<0.05) in the cutting olive branches at 25 cm length compared to other cutting lengths. There was a positive correlation between MN or MBM production and SCFA, PF, ED and a + b values. The greatest proportion of gas production occurred during the first 48 h of incubation. Microbial N and MBM production were positively correlated with a + b, SCFA, PF and ED.

The addition of PEG to the plant samples incubated with rumen fluid at a ratio of 2:1 PEG: substrate increased the values of gas production, characteristics of fermentation, MN, MBM, SCFA and ED. The response of the olive pruning branches to PEG treatment in terms of increased gas production varied between cutting lengths and tended to decline as incubation progressed, with the highest increase (17%) during the first 24 h of incubation. On the basis of the studies on nutritive parameters, olive pruning branches cut at 25 cm distance from the tip in diameter <3 mm were nutritionally well-suited as dietary supplements for ruminants.

Key words: degradability, gas production, microbial mass, polyethylene glycol


Introduction

Olea europaea L., an evergreen tree that belongs to the family Oleaceae, is widely spread in the Mediterranean regions. Both olive tree culture and olive oil industry generate substantial amounts of olive by-products, which essentially consist from pruning residues, leaves, stones, pulp, olive cake, and watery waste known as "olive molasses" (Molina-Alcaide and Yáňez-Ruiz 2008). The recycling of this wastes is of great attention as their storage causes serious problems from the environmental, social and economical point of view. An important alternative utilization olive tree pruning by-products and olive leaves would be as roughage feeds for ruminants (Fayed et al 2009; Paiva-Martins et al 2009). Such form of nutrition could improve the economy and the efficiency of animal production (Molina Alcaide and Nefzaoui 1996). Al-Masri (2001) studied the possibility of using olive cake together with animal waste to produce biogas. Olive cake represents a poor agricultural residue that cannot be used alone for ruminant nutrition because of the presence of high amounts of lignocellulosic materials which have low digestibility (Al-Masri and Günther 1999). Removal of the wood from olive cake to obtain olive cake pulp increased the organic matter digestibility, metabolizable energy and the volume of gas produced during fermentation (Al-Masri 2003). The inclusion of olive cake into multi-nutrient feed blocks has proved to be a promising way for their utilization (Ben Salem et al 2003; Molina-Alcaide et al 2005). Olive molasses has been used in diets for pregnant and lactating ewes (Aguilera et al 1992).

In Mediterranean countries, high amounts of olive branches are available following pruning in the late autumn or early winter seasons when natural roughages are not available to animals. Therefore, these by-products could be used as supplements. Olive trees are usually subjected to severe pruning every second year and light pruning in the alternate year at different cutting lengths (20-100 cm) according to the growth period of the tree (fruit or vegetative shoots) (Katana 1978; Albies et al 1985). The pruned branches require an adequate preservation. Air-drying for seven days in the shade at room temperature did not have detrimental effects on the nutritive value of olive leaves and could be a simple and low-cost procedure for their preservation (Martin-Garcia and Molina-Alcaide 2008).

The nutritive quality of the forage and its content of anti-nutritional components (tannins) are influenced by harvest management and cutting regimen (Al-Masri and Mardini 2008; Al-Masri 2010). The phenolic compounds (particularly tannins) in some shrubs and roughages may bind to protein, thus making the protein inaccessible to rumen microbes. Polyethylene glycol (PEG) is able to form complexes with tannins (Getachew et al 2000) and has been used to reduce tannin-protein complex formation or to release these complexes (Makkar et al 1995). The effect of different levels of PEG (2-200 g/100 g DM) on the chemical composition and nutritive value of olive leaves has been investigated (Martín García et al 2004). Cell wall constituents in olive leaves decreased and total extractable condensed tannins increased with increasing the amounts of PEG. The addition of PEG (2 g/100 g DM) increased organic matter digestibility of olive leaves. In contrast, Yáňez Ruiz et al (2004) found no effect of PEG (2.1 g/100 g DM) on the condensed tannins and rumen degradability of olive leaves. The effect of PEG on the nutritive value of olive trees pruning residues has been investigated (Al-Masri 2012). The addition of PEG to the samples of olive pruning branches incubated with rumen fluid at a ratio of 2:1 PEG: substrate increased the values of organic matter digestibility, matabolizable energy and net energy lactation.

Compared with other laboratory techniques, the gas-production technique has proved accurate in predicting animal performance and voluntary feed intake of roughages (Blümmel et al 2005) and was suggested as being more efficient than other in vitro techniques for determining the nutritive value of feeds containing anti-nutritive factors and for evaluating the microbial fermentation of ruminant feeds and its impact on fermentation products (Getachew et al 2005). In the gas production method, kinetics of fermentation can be studied by simply reading the increase in gas production at a series of chosen time intervals during incubation with rumen liquor and using the exponential equation P = a + b (1 – e-ct) (Řrskov and McDonald 1979). Gas production is associated with volatile fatty acid production following fermentation of substrate (Blümmel and Řrskov 1993). In addition, the application of models permits the fermentation kinetics of the soluble and readily degradable fraction of the feeds, and more slowly degradable fraction to be described (Getachew et al 1998).


Objectives

The objectives of the present study were:


Materials and methods

Plant materials tested

Branches (stems with leaves) of 12-year-old olive (Olea europaea) trees, grown at Der Al-Hajar research station about 30 km south east of Damascus in the arid steppe region, which receives a total annual precipitation of 100-120 mm, were hand-cut using a cutting shear in the routine pruning season at 25, 50, 75 or 100 cm distance from the tip (cutting length) (Photo 1). The pruning branches were less than 3, 4, 5, and 7 mm in diameter, respectively. The branches for each length range were collected with 4 replicates (n = 4) (5 trees each), dried at room temperature (20-25 oC) for 6 days, ground to pass through a 1-mm sieve and stored frozen at -20 oC in sealed nylon bags for later analysis and determination. The nutritive components (g/kg DM) in olive pruning branches were: 71.9, 66.3, 57.8, 44.6 crude protein, 94.0, 96.9, 97.8, 100 lignin, 406, 434, 474, 496 neutral-detergent fiber, 17.0, 17.4, 17.1, 17.0 tannins and 2.45, 2.26, 2.06, 1.41 buffer soluble nitrogen (BS-N) for the cutting lengths 25, 50, 75 and 100 cm, respectively (Al-Masri 2012).

Photo 1.  Pruned branches of olive trees cut at 25, 50, 75 and 100 cm distance from the tip.
Study of fermentation kinetics

The experimental samples were incubated in 100-mL calibrated glass syringes at 39oC with the ruminal fluid mixed with the medium, based on a modified procedure of Menke et al (1979) to determine the rate of gas production during 96 h incubation. As a modification, the syringes were incubated standing upright in a water-bath instead of being stacked horizontally on a slowly turning rotor housed in an incubator (Blümmel and Řrskov 1993). The method of Menke et al (1979) was used to study the digestion kinetics of plant samples, utilizing the exponential equation P = a + b (1 – e-ct) of Řrskov and McDonald (1979), and to evaluate the biological activity of tannins according to Makkar et al (1995) with or without adding polyethylene glycol to the rumen fluid mixture over 96 h of in vitro incubation. Gas production with or without adding polyethylene glycol (PEG, 6000; Fluka Firm No. 81260) at a ratio of 2:1 PEG:substrate was recorded after 3, 5, 8, 10, 24, 30, 48, 72 and 96 h of incubation. Gas production from the experimental sample was calculated by subtracting the volume of gas produced from the blank with or without the addition of PEG. Details of rumen fluid collection and methods of incubation have been described previously (Al-Masri 2015).

Determination of microbial nitrogen and biomass

15N-labelled ammonium sulphate (>98% 15N) was added to 30 mL of the rumen fluid mixture and incubated for 96 h with the samples (200 mg), with or without added PEG, to estimate the microbial nitrogen (MN) and microbial biomass (MBM) production (Al-Masri 2010). Total nitrogen, as well as 15N atom excess in the N pool of the sample and fluid mixture incubated for 96 h or in the fluid mixture alone (blank) were measured with an emission spectrometer (JASCO N-150, Japan Spectroscopic Com. Ltd, Tokyo, Japan). The following equations were used to estimate MN and MBM production:

MN (mg/96 h/200 mg sample) = [1 – (%15N atom excess in the N-pool of the sample and fluid mixture incubated for 96 h / %15N atom excess in the fluid mixture)]* mg N in the sample incubated for 96h.

MBM (mg/96 h/200 mg sample) = MN / 0.0864

Czerkawski (1986) indicated that the rumen microbes contain 8.64% nitrogen.

Calculations

The effective degradability (ED) of dry matter was calculated assuming that ruminal outflow rate (k) is 0.04/h for sheep (Umunna et al 1995) as: ED (%) = a + [(b * c) / (c + k)]. The volume of gas was based on that produced from 200 mg substrate.

The partitioning factor (PF) is calculated as the ratio of substrate effective degraded dry matter in vitro (mg) to the volume of gas (ml) produced by it after 96 h of incubation. PF is an indicator of forage quality (Blümmel et al 1997), and greater PF reveals the better quality of forage.

Short chain fatty acids (SCFA) concentration was calculated according to Getachew et al (2002) as: SCFA (m mol/200 mg DM) = 0.0222 GP – 0.00425. Where GP is the net gas production (mL/200 mg DM) after 24 h of incubation.

Data and statistical analyses

Data on gas production were fitted to the exponential equation P = a + b (1 – e-ct) of Řrskov and McDonald (1979), where P (mL) was defined as gas production at time t, a (mL) was the initial gas produced from soluble fraction, b (mL) was the gas production during incubation which is produced from insoluble but fermentable fraction, a + b (mL) was the potential gas production and c was the fractional rate of gas production per hour.

A factorial design was used in this experiment, with tow fixed factors: (1) cutting length; (2) polyethylene glycol treatment (PEG or no PEG). Results were subjected to analysis of variance (ANOVA) using a Statview-IV program (Abacus Concepts, Berkeley, CA, USA) to test the effect of cutting length and PEG treatment. Means were separated using the Fisher’s least significant difference test at the 95% confidence level. Regression coefficients (R) between the studied parameters were calculated.


Results and discussion

Gas production and fermentation kinetics

The changes in cumulative gas production from the branches of olive tree, as a result of cutting length, after incubation with or without PEG for 96 h and their fermentation kinetics are presented in Table 1. Cutting length of the olive branches positively affected the in vitro gas production after 24, 48, 72 and 96 h and the potential gas production (a + b) levels. The values of gas production during incubation (b) and fractional rate of gas production (c) declined with the increase in cutting length (P<0.05). The intake of a feed is mostly explained by the fractional rate of gas production which affects the passage rate of feed through the rumen, whereas the potential gas production, is associated with degradability of feed (Khazaal et al 1995). Therefore the higher values obtained for the fractional rate of gas and potential gas production in the cutting branches at 25 cm length might indicate a better nutritive availability for rumen micro-organisms. These results are in agreement with Al-Masri (2012) who indicated that the olive branches cut at 25 cm distance from the tip gave significantly (P < 0.05) higher values of digestible organic matter, metabolizable energy and buffer soluble nitrogen compared with other cutting lengths (50, 75 or 100 cm), indicating a higher solubility of nitrogen at the former length (25 cm) which included a large amount leaves. The average proportions of leaf (dry matter basis) in the pruned branches cut at 25, 50, 75 and 100 cm of length amounted to 0.69, 0.61, 0.52 and 0.44, respectively. Kafilzadeh and Heidary (2013) indicated that in any evaluation of oat varieties, not only yield and digestibility but also kinetics of fermentation should be taken into consideration. The fractional rate of gas production of forages produced from 18 different varieties of oat (Avena sativa L.) ranged from 0.029 to 0.040/h. In a study with different roughages (oat straw, bean straw, maize stubble, agave bagass), Oritiz-Tovar et al (2007) reported that the c values and potential gas production ranged from 0.028 to 0.076/h and from 110 to 142 mL/g DM for all roughages, respectively.

Al-Masri (2015) reported that the values of a + b and fractional rate of gas production of leaves of some salt-tolerant tree species (Tamarix articulata Vahl., Tamarix aphylla (L) Karst, Acacia ampliceps Maslin, Casuarina equisetifolia L, Parkinsonia aculeate L, Eucaliptus camaldulensis Dahnhard) ranged from 24 to 38 mL/g DM and from 0.056 to 0.088/h, respectively. Al-Masri (2010) indicated that the branches of Kochia indica cut at 30 cm distance from the tip had lower c value (0.034/h) than those cut at 15 cm length (0.041/h). The values of potential gas production (36-47 mL/g DM) or fractional rate of gas production (0.042-0.057/h) of the experimental olive pruning branches are lower or higher to those (228 mL/g DM or 0.015/h, respectively), reported by Sallam et al (2008) for alfalfa hay.

Table 1. Cumulative gas production in vitro from the olive tree branches of the different lengths after incubation with or without polyethylene glycol (PEG, 6000) for 96 h and the characteristics of fermentation after incubation obtained by fitting data of gas production after 3, 5, 8,10, 24, 30, 48, 72 and 96 h incubation to the equation P = a + b (1 - e-ct ).

Gas production (mL/200 mg DM)

Gas production constants

24 h

48 h

72 h

96 h

a

b

a + b

c

Length (cm) (pooled)

25

35.3a

44.4a

46.3a

46.6a

1.59b

48.5a

46.9a

0.057a

50

30.7b

39.9b

42.1b

42.5b

1.30b

44.4b

43.1b

0.052b

75

26.7c

37.1c

38.2c

38.4c

0.54a

39.9c

39.4c

0.049c

100

21.1d

33.1d

34.1d

34.5d

0.54a

36.3d

35.8d

0.042d

S.E.M

0.87

0.5

1.09

0.68

0.17

0.73

0.60

0.002

PEG treatment (pooled)

+

30.6a

39.8a

41.8a

42.2a

1.27b

44.0a

42.7a

0.052a

-

26.3b

37.4b

38.6b

38.9b

0.71a

40.6b

39.9b

0.048b

S.E.M

1.37

1.08

1.18

1.18

0.15

1.20

1.08

0.002

p

Length

<0.0001

<0.0001

<0.0001

<0.0001

<0.0001

<0.0001

<0.0001

<0.0001

PEG treatment

<0.0001

<0.0001

<0.0001

<0.0001

0.0008

<0.0001

<0.0001

<0.0003

Length-PEG interaction

0.2869

0.2588

0.5891

0.5100

0.8798

0.5117

0.4207

0.3190

a,b,c,d Means in the same columns for each parameter with different superscripts are different at P<0.05.
a, initial gas production (mL/200 mg DM), b: gas production during incubation (mL/200 mg DM);
a + b: potential gas production (mL/200 mg DM); c: fractional rate of gas production per hour.
S.E.M: standard error of the means.
PEG: polyethylene glycol ('+' with, '-' without).

The highest cumulative gas production was obtained during the first 48 h of incubation for the experimental pruning samples without addition of PEG (Fig. 1). Gas production reflects the degradation of dietary organic matter (OM) and more gas production, more degradation of OM (Groot et al 1996). The amount of gas produced per unit fermented material reflects the level of fermentation of the roughages. High CH4 production from ruminants is undesirable from both economic and environmental aspects. Olive branches cut at 25 cm distance from the tip produced higher (P<0.05) amounts of gas than those cut at 50, 75 and 100 cm lengths. This may be attributed to the high amounts of crude protein and low concentrations of lignocellolosic materials in the cutting branches at 25 cm length. Indeed the higher lignin (99 g/kg DM) and neutral detergent fibre (NDF) (485 g/kg DM) levels in the cutting branches at 75 and 100 cm lengths are almost certainly responsible for its reduced gas production versus the other cutting lengths (95 and 420 g/kg DM, respectively) (Al-Masri 2012).

Figure 1. Cumulativa gas production (in vitro) over 96 h from the olive tree
branches cut 25,50,75 and 100 cm distance from the tip

Gas production parameters suggested differences in nutritional value that were generally closely related to chemical composition (Cerrillo and Juárez 2004; Kamalak et al 2005; Salem 2005; Al-Masri 2010). Differences in potential gas production (a + b; potential degradability) among pruning samples could also be due to the extent of lignification of NDF. Lower NDF concentrations mean greater amounts of soluble cell walls which are available for fermentation. There is a negative relationship between gas production and cell wall content of diet (Getachew et al 2004). In our results, thea + b values were negatively correlated with lignin (R = -0.81; P<0.0001 and ) and NDF contents (R = -0.95; P<0.0001) and positively correlated with SCFA concentrations (R = 0.98; P<0.0001). The values of fractional rate of gas production (c) were negatively correlated with lignin (R = -0.43; P = 0.0033) and positively correlated with crude protein concentrations (R = 0.92; P<0.0001). However, there was a positive correlation between c and SCFA values (R = 0.88; P<0.0001). Al-Masri (2012) indicated that the values of digestible organic matter for the same experimental olive pruning branches were negatively correlated with lignin (R = -0.79; P<0.001) but positively correlated with crude protein (R = 0.94; P<0.001).

Figure 2. Increase (%) in gas production from the olive tree branches cut 25,50,75 and 100 cm distance
from the tip over 96 h incubation, as a result of addition of polyethylene gycol.

Secondary compounds such as tannins affect ruminal fermentation and forage degradability (Al-Masri 2015). There was a positive significant effect of PEG on the values of gas production and fermentation characteristics of the experimental olive pruning branches (Table 1). Karabulut et al (2006) indicated that PEG supplementation increased the values of organic matter digestibility (OMD), metabolizable energy (ME) and gas production characteristics (a and a + b) expect of gas production rate ( c ) of leaves of Olea europaea. The improvement in gas production, OMD and ME with PEG emphasizes the negative effect of tannins on digestibility. Martín Farcía et al (2004) reported that treatment of olive by-products (olive cake and olive leaves) with PEG (2 g of PEG/100 g of by-product) increased total extractable condensed tannins and in vitro organic matter digestibility and improved nutrient availability either at the rumen and intestine level. Our results indicated that the increase (%) in gas production from the experimental olive branches as a result of PEG treatment was not stable over the incubation period (Fig. 2). The response of the olive pruning branches to PEG treatment in terms of increased gas production varied between cutting lengths and tended to decline as incubation progressed, with the highest increase (17%) during the first 24 h of incubation. This was most obvious with cutting length at 100 cm where the increase reached over 20% at 24 h but decreased to 11% after 96 h incubation. To some extents similar behaviour was observed with cutting branches at 75 cm length. These findings indicate the microbes can adapt or overcome some of the anti-nutritive effects.

Microbial nitrogen and biomass

The average amount of microbial nitrogen (MN) or microbial biomass (MBM) produced from g substrate varied with cutting length of the branches of olive trees (Table 2). The olive branches cut at 25 and 50 cm distance from the tip produced higher (P<0.05) amounts of MN (0.53 mg/g DM) than those cut at 75 and 100 cm lengths (0.30 mg/g DM). Corresponding values for MBM were 6.14 mg/g DM or 3.42 mg/g DM for cutting lengths of the branches performed at 25 and 50 cm or at 75 and 100 cm, respectively. The decline in the MN and MBN values with increase cutting length of the branches were to be expected since there were negative correlations between the MN and MBM values and NDF concentrations (R = -0.63; P<0.01) and positive correlations between MN and MBM values and crude protein contents (R = 0.67; P = 0.0045). Similar correlations between MN and MBM values and lignin (R = -0.89; P<0.001) and crude protein concentrations (R = 0.83; P<0.01) of the branches of kochia indica cut at different lengths (15 or 30 cm) (Al-Masri 2010).

Table 2. Changes in the microbial nitrogen (MN), microbial biomass (MBM), short chain fatty acids (SCFA), effective degradability (ED), partitioning factor (PF) and the ratios of the MN or MBM to effective degraded substrate (EDS) of the olive tree branches of the different lengths after incubation with or without polyethylene glycol.

MN
(mg/g DM)

MBM
(mg/g DM)

SCFA
(m mol/g DM)

ED
(%)

PF

mg MN /
g EDS

mg MBM /
g EDS

Length (cm) (pooled)

25

0.62a

7.18a

3.90a

26.8a

1.15a

2.30a

26.6a

50

0.44ab

5.09ab

3.38b

23.8b

1.12ab

1.82ab

21.1ab

75

0.34b

3.94b

2.94c

21.4c

1.11b

1.59ab

18.4ab

100

0.25b

2.89b

2.32d

18.1d

1.05c

1.38b

15.9b

S.E.M

0.07

0.88

0.10

0.46

0.01

0.3

3.51

PEG treatment (pooled)

+

0.52a

6.02a

3.38a

23.7a

1.12a

2.14a

24.8a

-

0.31b

3.59b

2.98b

21.4b

1.10a

1.40b

16.3b

S.E.M

0.06

0.69

0.15

0.84

0.01

0.20

2.3

P

Length

0.0090

0.0090

<0.0001

<0.0001

<0.0001

0.1798

0.1730

PEG treatment

0.0072

0.0072

<0.0001

<0.0001

0.0901

0.0195

0.0194

Length-PEG interaction

0.6203

0.6210

0.2869

0.5676

0.4360

0.8278

0.8298

a,b,c,d Means in the same columns for each parameter with different superscript are different at P<0.05.
S.E.M: standard error of the means.
PEG: polyethylene glycol ('+' with, '-' without).

The net MN or biomass production would depend on the balance between decreased degradable dry matter and higher microbial mass production per unit dry matter digested. Al-Masri (2010) reported that the average amount of MN produced from g substrate of the branches of Kochia indica amounted to 12 mg for the branches cut at 30 cm distance from the tip and 16 mg for cutting length of the branches performed at 15 cm. Cone and Van Gelder (2000) established microbial efficiency at the time of estimated maximum microbial biomass and determined efficiency of microbial protein using microbial purines. They observed increased microbial efficiency for substrates with higher fermentation rates and obtained negative microbial efficiency values with some slowly degradable substrates. Substrates with high fermentation rates may have high yield of microbial protein by decreasing the proportion of energy used for maintenance purposes (Cone and Van Gelder 2000). In our results, the values of effective degradability (ED), partitioning factor (PF), short chain fatty acids (SCFA) and the ratios of microbial N or biomass production to effective degraded substrate (EDS) were significantly higher (P<0.05) in the cutting olive branches at 25 cm length compared to other cutting lengths (Table 2). The values of MN or MBM production were positively correlated with potential gas production (R = 0.58; P = 0.0184), SCFA (R = 0.66; P = 0.0053) and PF and effective degradability ( R = 0.68; P = 0.0035) and negatively correlated with NDF contents (R = -0.63; P<0.01).

Table 3. The increases in the values of potential gas production (a + b), short chain fatty acid (SCFA) and microbial nitrogen (MN) of olive tree branches of the different lengths as a result of polyethylene glycol treatment.

Length (cm)

a + b (mL/g DM)

Increase

SCFA (m mol/g DM)

Increase

MN (mg/g DM)

Increase

-PEG

+PEG

-PEG

+PEG

-PEG

+PEG

25

229a

240a

11a

3.63a

4.17a

0.54a

0.43a

0.81a

0.38a

50

209b

222b

13a

3.10b

3.67b

0.57a

0.35ab

0.52ab

0.17a

75

189c

205c

16a

2.72c

3.16c

0.44a

0.28ab

0.41b

0.13a

100

171d

188d

17a

2.11d

2.52d

0.41a

0.17b

0.33b

0.16a

S.E.M

2.28

1.64

2.07

0.05

0.04

0.06

0.06

0.12

0.11

p

<0.0001

<0.0001

0.1811

<0.0001

<0.0001

0.3106

0.0763

0.0954

0.4539

abcd Means in the same columns for each parameter with different superscript are different at P<0.05.
S.E.M: standard error of the means.
PEG: polyethylene glycol ('+' with, '-' without).

The addition of PEG in the fermentation process increased the values of a + b, SCFA and MN for the experimental olive branches and amounted in average to 14 mL/g DM, 0.49 m mol/g DM and 0.21 mg/g DM, respectively (Table 3). This allied with higher production of microbial nitrogen in the presence of PEG, suggests that the PEG might have bound with tannins, releasing proteins for microbial breakdown. Pritchard et al (1988) indicated that the low intake and feed value of mulga (Accacia aneura) leaf was related to its content of condensed tannins, which bound with proteins in the leaves. Our results indicated that the MN or MBM values were negatively correlated with total tannin concentrations (R = -0.32; P = -0.2333) and positively correlated with buffer soluble nitrogen contents (BS-N) (R = 0.89; P = 0.1073). Al-Masri and Mardini (2008) indicated that the BS-N concentrations in leaves and stalks of Sesbania aculeate and Kochia indica harvested at different maturity stages were negatively correlated with condensed tannins (R = -0.81; P = -0.56). The higher gas production, SCFA, MN and MBM production following inclusion of PEG in our study are in agreement with Al-Masri (2015). Addition of PEG can be advantageous if the tannin content of the feed is sufficiently high to the extent that it depresses microbial activity and digestibility of feeds drastically Getachew et al (2000). A rapid degradation of nitrogen not matched with energy availability could lead to accumulation of NH3-N in the in vitro system or to a high absorption of NH 3-N from the rumen in vivo. Synchronization of the rate of degradation of nitrogen and carbohydrate components in the rumen is extremely important for efficient utilization of rumen NH3-N for synthesis of microbial protein.


Conclusions

Based on the results of this research it is concluded that:


Acknowledgements

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


References

Aguilera J F, García M A and Molina E 1992 The performance of ewes offered concentrates containing olive by-products in late pregnancy and lactating. Animal Production 55: 219-226.

Alibes X, Berge Ph, Martilotti F, Nefzaoui A and Zoipoulos P E 1985 Olive by-product for animal feed. Animal Production and Health Division, FAO, Rome, http:// www.fao.org/docrep/003/x6545E00.htm.

Al-Masri M R 2001 Changes in biogas production due to different ratios of some animal and agricultural wastes. Bioresource Technology 77: 97-100.

Al-Masri M R 2003 An in vitro e evaluation of some unconventional ruminant feeds in terms of the organic matter digestibility, energy and microbial biomass. Tropical Animal Health and Production 35: 155-167.

Al-Masri M R 2010 In vitro rumen fermentation kinetics and nutritional evaluation of Kochia indica as affected by harvest time and cutting regimen. Animal Feed Science and Technology 157: 55-63.

Al-Masri M R 2012 An in vitro nutritive evaluation of olive tree (Olea europaea)) pruning residues as affected by cutting regimen. Bioresource Technology 103: 234-248.

Al-Masri M R 2015 Nutritional evaluation of leaves of some salt-tolerant tree species by assessing, in vitro,, the ruminal microbial nitrogen and fermentation characteristics. Livestock Research for Rural Development 27 (2) 2015, http://www.lrrd.org/lrrd27/2/alma27036.html

Al-Masri M R and Günther K D 1999 Changes in digestibility and cell-wall constituents of some agricultural by-products due to gamma irradiation and urea treatments. Radiation Physics Chemistry 55: 323-329.

Al-Masri M R and Mardini M 2008 Nutritional and anti-nutritional components in Sesbania aculeate and Kochia indica at different harvest times. Journal of Applied Animal Research 34: 33-37.

Ben Salem H, Ben Salem I, Nefzaoui A and Ben Said M S 2003 Effect of PEG and olive cake feed blocks supply on feed intake, digestion, and health of goats given kermes oak (Quercus coccifera L.) foliage. Animal Feed Science and Technology 110: 45-59.

Blümmel M and Řrskov E R 1993 Comparison of in vitro gas production and nylon bag degradability of roughages in predicting feed intake in cattle. Animal Feed Science and Technology 40: 109-119.

Blümmel M, Cone J W, Van Gelder A H, Nshalai I, Umunna N N, Makkar H P S and Becker K 2005 Prediction of forage intake using in vitro gas production methods: Comparison of multiphase fermentation kinetics measured in an automated gas test, and combined gas volume and substrate degradability measurements in a manual syringe system. Animal Feed Science and Technology 123-124: 517-526.

Blümmel M, Makkar H P S and Becker K 1997 In vitro gas production: a technique revisited. Animal Physiology and Animal Nutrition 77: 24-34.

Cerrillo M A and Juárez R A S 2004 In vitro gas production parameters in cacti and tree species commonly consumed by grazing goats in a semiarid region of North Mexico. Livestock Research for Rural Development 16 (4) 2004, http://www.lrrd.org/lrrd16/4/cerr16021.htm

Cone J W and Van Gelder A H 2000 In vitro microbial protein synthesis in rumen fluid estimated with the gas production technique. In: Gas Production: Fermentation Kinetics for Feed Evaluation to Assess Microbial Activity. British Society of Animal Science, Penicuik, UK, pp. 25-26.

Czerkawski J W 1986 An Introduction to Rumen Studies.Pergamon Press, Oxford.

Fayed A M, El-Ashry M A and Aziz H A 2009 Effect of feeding olive tree pruning by-products on sheep performance in Sinai. World Journal of Agricultural Science 5: 436-445.

Getachew G, Blümmel M, Makkar H P S and Becker K 1998 In vitro gas measuring techniques for assessment of nutritional quality of feeds: A review. Animal Feed Science and Technology 72: 261-281.

Getachew G, DePeters E J, Robinson P H and Fadel J G 2005 Use of an in vitro rumen gas production technique to evaluate microbial fermentation of ruminant feeds and its impact on fermentation products. Animal Feed Science and Technology 123-124: 547-559.

Getachew G, Makkar H P S and Becker K 2000 Effect of polyethylene glycol on in vitro degradability of nitrogen and microbial protein synthesis from tannin-rich browse and herbaceous legumes. British Journal of Nutrition 84: 73-83.

Getachew G, Makkar H P S and Becker K 2002 Tropical browses: contents of phenolic compounds, in vitro gas production and stoichiometric relationship between short chain fatty acid and in vitro gas production. Journal of Agricultural Science,Cambridge 139: 341-352.

Getachew G, Robinson P H, Depeters E J and Taylor S J 2004 Relationships between chemical composition dry matter degradation and in vitro gas production of several ruminant feeds. Animal Feed Science and Technology 111: 51-57.

Groot J C J, Cone J W, Williams B A, Debersaques F M A and Lantinga E A 1996 Multiphasic analysis of gas production kinetics for in vitro fermentation of in vitro fermentation of ruminant feeds. Animal Feed Science and Technology 64: 77–89.

Kafilzadeh F and Heidary N 2013 Chemical composition, in vitro digestibility and kinetics of fermentation of whole-crop forage from 18 different varieties of oat (Avena sativa L.). Journal of Applied Animal Research 41: 61-68.

Kamalak A, Canbolat O, Gurbuz Y, Ozay O and Ozkose E 2005 Chemical composition and its relationship to in vitro gas production of several tannin containing tree and shrubs leaves. Asian-Australian Journal of Animal Science 18: 203-208.

Karabulut A, Canbolat O, Ozkan C O and Kamalak A 2006 Potential nutritive value of some Mediterranean shrub and tree leaves as emergency food for sheep in winter. Livestock Research for Rural Development 18 (6) 2006, http://www.lrrd.org/lrrd18/6/kara18081.htm

Katana H 1987 Fruit Production and Preservation. University of Damascus, Syria, pp. 499-542.

Khazaal K, Dentinho J M, Ribeiro J M and Řrskov E R 1995 Prediction of apparent digestibility and voluntary intake of hays fed to sheep: comparison between using fibre components, in vitro digestibility or characteristics of gas production or nylon bag degradation. Animal Science 61: 527-538.

Makkar H P S, Blümmel M and Becker K 1995 Formation of complexes between polyvinyl pyrrolidones or polyethylene glycols and tannins, and their implication in gas production and true digestibility in vitro techniques. British Journal of Nutrition 73: 897-913.

Martín García A I, Yanez Ruiz D R, Moumen A and Molina Alcaide E 2004 Effect of polyethylene-glycol on the chemical composition and nutrient availability of olive (Olea europaea var. europaea) by-products. Animal Feed Science and Technology 114: 159-177.

Martín-García I and Molina-Alcaide E 2008 Effect of different drying procedures on the nutritive value of olive (Olea europaea var. europaea) leaves for ruminants. Animal Feed Science and Technology 142: 317-329.

Menke K H, Raab L, Salewski A, Steingass H, Fritz D and Schneider W 1979 The estimation of the digestibility and metabolizable energy content of ruminant feedstuffs from the gas production when they are incubated with rumen liquor in vitro. Journal of Agricultural Science, Cambridge 93: 217-222.

Molina-Alcaide E and Nefzaoui A 1996 Recycling of olive oil by-products: Possibilities of utilization in animal nutrition. International Biodeterioration and Biodegradation 38: 227-235.

Molina-Alcaide E and Yáňez-Ruiz DR 2008 Potential use of olive by-products in ruminant feeding: A review. Animal Feed Science and Technology 147: 247-264.

Molina-Alcaide E, Morales Garcia E Y and Martin Garcia A I 2005 Effect of feeding multi-nutrient blocks on rumen fermentation, intake, digestibility and milk yield and composition in dairy goats. In: Proceeding of the 11th Seminar of the Sub-Network FAO-CIHEAM on Sheep and Goat Nutrition. Catania, Italy, p. 77.

Řrskov E R and McDonald I 1979 The estimation of protein degradability in the rumen from incubation measurements weighted according to rate of passage. Journal of Agricultural Science, Cambridge 92: 499-503.

Ortiz-Tovar M G, López-Miranda J, Cerrillo-Soto M A, Juárez-Reyes A, Favela-Torres E and Soto-Cruz N 2007 Effect of solid substrate fermentation on the nutritional quality of agro-industrial residues. Interciencia 32: 339-343.

Paiva-Martins F, Barbosa S, Pinherio V, Mourao J L and Outro-Monteiro D 2009 The effect of olive leaves supplementation on the feed digestibility, growth performances of pigs and quality of pork meat. Meat Science 82: 438-443.

Pritchard D A, Stocks D C, O'sullivan B M, Martin P R, Hurwood I S and O'rourke P K 1988 The effect of polyethylene glycol (PEG) on wool growth and live weight of sheep consuming mulga (Acacia aneura) diet. Proceedings of the Australian Society of Animal Production 17: 290-293.

Salem A Z M 2005 Impact of season of harvest on in vitro gas production and dry matter degradability of Acacia saligna leaves with inoculum from three ruminant species. Animal Feed Science and Technology 123-124: 67-79.

Sallam S M A, Buenob I C S, Godoyb P B, Nozellab E F, Vittib D M S S and Abdallab A L 2008 Nutritive value assessment of artichoke (Cynara scolymus) by-products as an alternative feed resource for ruminants. Tropical and Subtropical Agroecosystems 8: 181-189.

Umunna N N, Nsahlai I V and Osuiji O 1995 Degradability of forage protein supplements and their effects on the kinetics of digestion and passage. Small Ruminant Research 17: 145-152.

Yáňez Ruiz D R, Martín García A I, Moumen A and Molina Alcaide E 2004 Ruminal fermentation and degradation patterns, protozoa population and urinary purine derivatives excretion in goats and wethers fed diets based on olive leaves. Journal of Animal Science 82: 3006-3014.


Received 19 April 2016; Accepted 16 July 2016; Published 1 August 2016

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