The effect of harvest stage on the potential nutritive value of kermes oak (Quercus coccifera) leaves

C Ataşoğlu, S Şahin, Ö Canbolat* and H Baytekin**

Çanakkale Onsekiz Mart University, Department of Animal Science, 17020, Çanakkale, Turkey
* Uludağ University, Department of Animal Science, Bursa, Turkey
** Çanakkale Onsekiz Mart University, Department of Field Crops, 17020, Çanakkale, Turkey
catasoglu@comu.edu.tr

Abstract

The aim of the current study was to determine the effect of harvesting stage on the potential nutritive value of oak leaves using the chemical composition and in vitro gas production technique. The oak leaves were harvested in May, July, September and October of 2006 and analysed for their chemical composition. Gas production was recorded before incubation (0) and 3, 6, 12, 24, 48, 72 and 96 h after incubation.

 

The harvest stage had a significant effect on chemical composition and in vitro gas production and the kinetics. The crude protein (CP) and ether extract (EE) content did not differ among the harvest stages (P>0.05). In contrast, the NDF, ADF and ADL contents increased (P<0.01) as the vegetation progressed. The condensed tannin content fluctuated (P<0.001) throughout the study. Generally the gas production of the oak leaves obtained in September and October was higher than those obtained in May and July. The rate of gas production, metabolisable energy (ME) and organic matter digestibility (OMD) values were also highest in October followed by in September, July and May.

 

In conclusion, harvest stage influences the nutritional quality of kermes oak leaves with most of the nutritional parameters determined here being higher in autumn than in summer and spring.    

Key Words: Digestibility, metabolisable energy, natural resource, oak leaves, ruminant

Introduction

Climate models suggest that a significant reduction in the amount of precipitation is expected in a significant part of the subtropical zone including East Mediterranean basin and Turkey. Predictions on countries in this region, which will adversely be affected by global warming, are the reduction of natural water resources, forest fires, draught, desertification and ecological disruptions (Rubio 2009). This will create a serious problem of the sustainability of animal production systems especially for ruminants in the future. In this regard, the feeding of goats and sheep is likely to become more dependent on the use of natural resources such as shrublands.

 

Kermes oak (Quercus coccifera) is one of the significant shrub species in the maquis vegetation of the East Mediterranean basin (Papanastasis et al 2008). Understanding of the nutritional characteristics of this shrub species is important for its proper utilisation by grazing animals. Chemical composition, in combination with in vitro gas production, OMD and ME content are widely used to determine the potential nutritive value of shrub and tree leaves which are previously limited or uninvestigated (Kamalak et al 2004, Karabulut et al 2007). The aim of this study was to investigate the influence of harvest stage on the nutritive value of kermes oak leaves. 

 

Materials and methods 

Leaf samples

 

Leaves of kermes oak were harvested by hand from 5 different trees in May, July, September and October of 2006 in a shrubland browsed by goats of Çanakkale Province in Turkey. The samples were dried on the bench in the laboratory and ground to pass through 1 mm sieve for subsequent analysis. The area was located at altitude of 36 m above sea level. The mean annual rainfall and temperature were 505 mm and 14.8 ^oC, respectively.

 

Chemical analysis

 

All the samples were analyzed according to the methods of AOAC (2000) crude protein (method 990.03), ether extract (method 2003.05) and ash (method 942.05). Neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) analyses were carried out as described by Van Soest et al (1991). Heat stable amylase was not used in NDF determination and NDF was expressed with residual ash. Condensed tannin (CT) was determined by butanol-HCl method as described by Makkar et al (1995). All chemical analyses were carried out in triplicate.

 

In vitro incubations

 

Rumen fluid was obtained from two fistulated sheep fed twice daily with a diet containing alfalfa hay (60%) and concentrate (40%). Approximately 0.200 gram samples were incubated in vitro with rumen fluid following the procedures of Menke et al (1979). Gas production was recorded before incubation (0) and 3, 6, 12, 24, 48, 72 and 96 h after incubation. Total gas values were corrected for blank. Cumulative gas production data were fitted to the exponential equation: y = a + b (1-exp^-ct) (Ørskov and McDonald 1979),

 

Where y is the gas production at time t; a is the gas production from the immediately soluble fraction (mL), b is the gas production from the insoluble fraction (mL), c is the gas production rate constant, t = incubation time (h).

 

The ME (MJ/kg DM) of samples was calculated using equations of Menke et al (1979) as follows:

 

ME (MJ/kg DM) = 2.20 + 0.136 GP + 0.057 CP  R2=0.94

Where,

GP is 24 h net gas production (ml/200 mg),

CP = Crude protein, %

 

The OMD of samples was calculated using equations of Menke et al (1979) as follows:

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

Where,

GP is 24 h net gas production (ml / 200 mg),

CP = Crude protein, %

XA = Ash content, %

 

Statistical analysis

 

One-way analysis of variance (ANOVA) was carried out to compare the mean chemical composition, gas production, estimated parameters, in vitro OMD and ME values using General Linear Model (GLM) of Statistica for windows (Stastica, 1993). Significance between individual means was identified using the Tukey’s multiple range test. 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 

The chemical composition of kermes oak leaves is presented in Table 1.

The CP content did not differ among the harvest stages (P>0.05) reaching highest CP content in May. Similarly, no difference was found in EE content of the kermes oak samples obtained from different harvest stages. On the other hand, total cell wall (NDF) differed (P<0.01) among the harvest stages and ranged from 40.7 in May to 53.7 in July. A similar trend was also noted for ADF and ADL contents of the kermes oak leaves (P<0.01). Ash content did not fluctuate among the harvest stages (P>0.05). A significant variation was found in the CT content, ranging from 5.8 in May to 13.8% in September (P<0.001).

 

The chemical composition of shrubs has an impact on the consumption and utilization by sheep or goats (Decandia et al 2008). Shrub species are generally characterized by their low CP content and high lignin and tannin contents, which depend on species and plant phenological stages (Decandia et al 2008). As the vegetation progresses leading to the maturation of plants, the nutritional quality of shrub species deteriorates since CP content decreases and tannin level increases (Cabiddu et al 2000). The kermes oak studied here can be considered of low to moderate nutritional quality since it contains 7.0-9.0% CP, 40.7-53.7% NDF, 11.4-16.2% ADL and 5.8-13.8% CT on DM basis (Leng 1990). The CP content did not worsen in spite of the vegetation progress. This indicates that this shrub can sustain sufficient amounts of N for efficient ruminal fermentation in sheep and goats during the critical periods of the year, such as in summer when herbaceous vegetation is dry (Papanastasis et al 2006). Tannins are complex polyphenolic compounds with an ability to precipitate proteins and to form complexes with carbohydrates, thereby reducing the digestibility and utilization of nutrients in the gut (Kumar and Vaithiyanathan 1990). On the contrary, beneficial effects of tannins such as suppression of bloat and protection of dietary protein in the rumen are reported (Mueller-Harvey, 2006). The CT of the kermes oak fluctuated significantly reaching a maximum level with 13.8% in September and were generally higher than the nutritional critical levels of 2-4% on DM basis (Barry and McNabb 1999). However, nutritional significance of tannins depends on several factors such as the intake level and biological activity of tannins, ruminant species (sheep vs. goat) and the use of polyethylene glycol (Decandia et al 2008).         

 

The in vitro gas production system is regarded as a reliable and suitable tool in feed evaluation since gas production is reported to be well correlated with microbial protein synthesis and in vitro digestibility (Getachew et al 1998). The effect of harvesting stage of kermes oak leaves on in vitro gas production and the kinetics is given in Table 2. 

The harvest stage had a significant effect on in vitro gas production and the kinetics. Generally the gas production of the oak leaves obtained in September and October was higher than those obtained in May and July. The high extent of gas production from the samples harvested in September and October may be attributed to higher nutrient availability than in May and July with the OM fermented to yield short chain fatty acids and hence high gas volumes (Osuga et al 2008) or a possible adaptation of microorganisms to structural carbohydrates and tannins (Ammar et al 2005). On the other hand, low gas production from the samples with less NDF content in May might be associated with a better synchrony of energy and nitrogen release for microbial protein synthesis or polysaccharides storage in the microbial cells (Kim et al 1999). An inverse relation between gas production and microbial yield was also reported by Blümmel and Becker (1997). The gas production rate, ME and OMD of the oak leaves obtained in October was significantly (P<0.001) higher than those obtained in May, July and October.

 

Conclusion 

• The results of the chemical composition and in vitro gas production suggest that nutritional quality of kermes oak leaves varied depending upon the harvest stage and could likely maintain sufficient nutritional levels in sheep or goats.    

References 

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