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In sacco degradability, chemical and morphological composition of 15 varieties of European rice straw
Animal Feed Science and Technology 94 (2001) 15±27
In sacco degradability, chemical and morphological composition of 15 varieties of European rice straw Ahoefa Agbagla-Dohnania, Pierre NozieÁrea,*, Guy CleÂmentb, Michel Doreaua a
Equipe Digestion et Absorption des Nutriments, Unite de Recherches sur les Herbivores (URH), INRA site de Theix, 63122 St. GeneÁs Champanelle, France b CIRAD-CA, Montpellier, France Received 9 March 2001; received in revised form 7 August 2001; accepted 29 August 2001
Abstract The aim of this study was to evaluate the variability in chemical and morphological variables of European rice straw varieties and to relate these variations to changes in in sacco degradation. Fifteen rice straw varieties were analyzed for their chemical and morphological compositions. Ground (2 mm) straw was incubated in the rumen of three ruminally cannulated cows for 24 and 72 h for in sacco degradability measurements. Results were analyzed by principal component analysis (PCA) and equations are proposed for degradation of rice straw in the rumen according to morphological and chemical variables. Both chemical and morphological characteristics presented great variability. Mean values, on a dry matter (DM) basis (%), for ash, silica, crude protein (CP), ash-free neutral detergent ®ber (NDF), ash-free acid detergent ®ber (ADF), and acid detergent lignin (ADL), were 11.2, 6.8, 3.9, 75.8, 45.7 and 9.3 respectively. Mean values, on a DM basis (%), for stem (internodes nodes), leaf blade, leaf sheath and chaff were 22.7, 32.7, 35.8 and 7.5 respectively. Variation in the in sacco degradation (%) of DM and organic matter (OM) was observed among straw varieties at 24 and 72 h: 30.4 (26.6±36.3) and 50.3 (43.6±57.6) for DM degradation; 29.0 (23.6±35.6) and 50.2 (42.2±58.7) for OM. The principal component analysis discriminated degradation parameters with botanical and chemical parameters. Degradation (%) was positively related to total leaves and leaf blade fractions and hemicelluloses, and negatively related to stem fraction, NDF, cellulose and lignin. Cumulative equation with both leaf blades (morphological variable) and hemicelluloses (chemical variable) explained 62 and 66% of variation in OM degradation at 24 and 72 h, respectively. # 2001 Published by Elsevier Science B.V. Keywords: Rice straw; Cell wall components; Morphological fractions; In sacco degradation *
Corresponding author. Tel.: 33-473-624-686; fax: 33-473-624-273. E-mail address: [email protected] (P. NozieÁre). 0377-8401/01/$ ± see front matter # 2001 Published by Elsevier Science B.V. PII: S 0 3 7 7 - 8 4 0 1 ( 0 1 ) 0 0 2 9 6 - 6
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1. Introduction Rice is principally produced for human consumption and a large amount of straw is left in the ®eld. Rice straw constitutes a source of carbohydrates for ruminants in countries where it is produced. However, it has high lignin and low nitrogen contents which in combination are responsible for its low nutritive value. Many attempts have been made to improve its nutritive value, especially by chemical treatments (Rahal et al., 1997; Abou-ElEnin et al., 1999; Vadiveloo, 2000). Supplementing rice straw with concentrates (Wanapat et al., 1996; Mawuenyegah et al., 1997), with by-products such as niebe or blackgram straw (Reddy, 1997) showed some ef®ciency for animal feeding. Researchers have shown that selection could improve the nutritive value of rice (Bainton et al., 1986; Vadiveloo, 1995) and other cereal (Erickson et al., 1982; Flachowsky et al., 1991; Mathison et al., 1999) straws without negatively affecting their agronomic characteristics. Nevertheless, variability is an important subject that must be discussed when applying these varying approaches. Rice straw from Asia and United States has shown great variability in chemical composition (Vadiveloo, 1995; Abou-El-Enin et al., 1999), proportion of morphological fractions (Vadiveloo, 1995) and digestibility as estimated by in vitro (Vadiveloo, 1995; Williams et al., 1996) or in sacco (Nakashima and érskov, 1990; Rahal et al., 1997; Abou-El-Enin et al., 1999) measurements, but less is known about variability in European varieties. In this work, the relationships between degradability and chemical and/or morphological characteristics of 15 European varieties of rice straw have been studied. These straw varieties were grown under identical agronomic conditions to avoid the interference of environment and agronomic practices. Chemical composition and morphological fractions were measured and in sacco degradation was assessed. 2. Materials and methods 2.1. Straws Fifteen rice straw varieties (lettered A to O) were collected at maturity after grain harvesting in November 1999, from the CIRAD experimental rice®eld station, Mas d'Adrien, Camargue, France. This location is within the Beaucaire plain, between the little RhoÃne and the Mediterranean coast. The varieties were from a selection trial and were grown under similar agronomic conditions on the same ®eld (3 ha), in plots (500 m2) separated by bunds. The soils of this region are of sandy alluvial type, pH > 7. Flooding and sowing were performed on the 12 and 13 March. Fertilizer (urea) was applied at midtillering (17 June) and at the initiation of panicle (6 or 16 July). Final draining of the rice®eld occurred on the 20 September. The names and some agronomic characteristics of these straw samples are given in Table 1. Straw samples were hand-harvested 10 cm above the ground. The quantity harvested was 10 kg for each variety. The straw samples were laid out in a ventilated barn and periodically turned to prevent fermentation. One month after harvest, most of the moisture having been removed (no moisture to the touch) by air-drying, the straw was oven-dried at 40 8C for 72 h.
Straw identification
Name, Genotype
Origin
Pilosity
Height (cm)
Grain type
Parasitism
A B C D E F G H I J K L M N O
3488 A 301±F1 ARIETE CRISTALAVA H1 MIARA±BW DEDALO MIARA±S DELTASIENNE MIARA±I MOLO ESTRELA±H (PYGMALION IRAT 122) PYGMALION±A1 RINGO MIARA±AC SP 81 SP 91 SP 92 SP 93 ST 25/87 MIARA±R THAIÈBONNET THAIÈBONNET MIARA±AF
France Italy France France France France France France France France France France France United States France
Smooth Villous Smooth Villous Villous Less villous Less villous Villous Smooth Smooth Smooth Smooth Less villous Smooth Smooth
70 85 85 80 65 80 80 80 80 80 65 65 80 75 60
Long Long Long Long Long Long Long Long Long Long Long Long Long Long Long
No S Chilo suppressalis No MS Chilo suppressalis MR Fusarium roseum S Sclerotium sp. No MS Chilo suppressalis No No No No No MR Chilo suppressalis No
a
slender large slender slender large slender slender large slender large slender slender slender slender slender
No: no parasitism in straw. MR, MS, S, indicate the degree of sensibility to parasitism: moderate resistant, moderate susceptible, susceptible.
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Table 1 Name, origin, height, grain type and susceptibility to parasitism of rice strawsa
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2.2. Morphological analyses of straw samples The relative proportion by weight of leaf blade, leaf sheath, stem and chaff in approximately 200 g of whole straw was estimated in quadruplicate. Leaves were removed from internodes by cutting the stems above the nodes. Nodes plus internodes were pooled to constitute the stem fraction. Leaf sheath and leaf blade were separated. A miscellaneous fraction made of brittle parts (mainly leaf particles) was also determined. Total leaf proportion was calculated as the sum of leaf sheath, leaf blade and miscellaneous fraction. Part of the remaining straw was milled to pass through a 2 mm sieve for chemical analyses and in sacco studies. 2.3. Chemical analyses The straw samples were analyzed for total ash (550 8C, 6 h), neutral detergent ®ber (NDF), acid detergent ®ber (ADF) and acid detergent lignin (ADL) (Van Soest et al., 1991).1 Ash-free NDF and ADF were calculated from the determination of their ash content (Van Soest et al., 1991). Total silica (SiO2) was determined by the gravimetric method of hydro¯uoric acid evaporation (Horwitz, 1960). Crude protein (CP) content was calculated as N 6:25 from the total N determined by Dumas technique (AOAC, 1984). Analyses for total ash, silica and total N were performed in duplicate, and the others in triplicate. 2.4. In sacco degradation Three dry Holstein cows, average body weight of 805 21 kg, ®tted with permanent rumen cannulas were given a diet of 70% second cut of orchard grass hay and 30% concentrate (barley 43%, beet pulp 40%, soybean meal 10% and molasses 5%). The diet was distributed at a rate of 7 kg DM per day, in two equal meals at 09:00 and 17:00 h. Degradation measurements were made after 4 weeks of adaptation. Thirty dacron bags (Ankom Co, Fairport, NY, USA; pore size: 53 mm and internal dimensions: 5 cm 9 cm) per cow, i.e. 2 bags per feed, were ®lled with 2.5 g of straw and incubated in the rumen of the three cows for 24 and 72 h. The incubation sequence was repeated once. After incubation, the nylon bags were removed from the rumen, immediately rinsed in cold water and frozen. They were then machine-washed until water was clear: 5 cycles of 5 min, with cold water (approximately 10 l per cycle). The washed bags were oven-dried for 48 h at 60 8C and weighed. Residues were analyzed for ash and straw DM and OM disappearance values were calculated as the difference between weights before and after incubation of samples. 2.5. Statistical analyses Principal component analysis (PCA) of the data on degradation (OM degraded at 24 and 72 h), chemical composition (lignin, hemicelluloses, cellulose, SiO2, CP, and 1
This publicaton is no longer available. If this procedure was used, give the ``1991'' as the reference and specify procedural changes.
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morphological composition (stems, chaff, leaves), was carried out to quantify the contribution of each variable to the variation in degradation pattern of the straw. Four analyses were carried out, according to the variables: (1) lignin (ADL), hemicelluloses (being estimated from NDF and ADF), cellulose (being estimated from ADF and ADL), leaf blade and leaf sheath (PCA 1), (2) lignin, hemicelluloses (being estimated from ash-free NDF and ash-free ADF), cellulose (being estimated from ash-free ADF and ADL), leaf blade and leaf sheath (PCA 2), (3) lignin, hemicelluloses, cellulose (estimated from NDF, ADF and ADL), and total leaves (PCA 3) and (4) lignin, hemicelluloses, cellulose (estimated from ash-free ®ber residues and ADL), and total leaves (PCA 4). Single and multiple linear relationships between degradation and chemical and/or botanical parameters were calculated. All analyses were performed using SAS (1989). 3. Results and discussion 3.1. Chemical composition Straw composition, on a dry matter basis, was variable as shown in Table 2. Ash content of rice straw samples ranged from 9.6 for straw I to 14.1% for straw B. These values were very low compared to reported ash content in rice straw samples which averaged 14.1% in Philippine varieties (Bainton et al., 1987; Balasta et al., 1989), 16,6% in Asian varieties from other countries: India (Walli et al., 1988; Adya et al., 1995; Rahal et al., 1997), Japan Table 2 Chemical composition of rice straw samples (A to O), on a dry matter basis (%) Straw identification
Ash
NDF
Ash-free NDF
ADF
Ash-free ADF
ADL
Silica
CP
A B C D E F G H I J K L M N O
11.7 14.1 13.8 11.0 9.8 12.2 11.8 10.4 9.6 10.8 11.0 10.7 11.0 10.3 10.5
79.6 80.8 79.3 79.0 80.2 79.9 79.9 81.3 79.7 81.4 77.8 76.3 76.6 79.7 77.2
76.4 76.9 72.8 76.7 76.9 74.5 76.3 78.6 77.6 78.8 75.3 71.2 73.5 76.6 74.5
48.4 52.3 50.2 48.6 50.6 52.9 48.0 51.5 47.1 53.1 44.5 44.5 47.0 48.5 45.8
43.5 46.4 45.4 45.9 48.1 48.7 46.4 47.4 44.8 50.9 41.8 42.0 45.5 46.3 42.2
9.5 10.0 11.6 8.4 10.0 12.9 7.1 9.1 9.1 8.6 6.3 9.1 7.5 9.9 10.2
7.5 8.1 7.9 7.0 5.6 7.2 7.7 7.8 5.2 6.3 6.7 6.3 6.6 6.1 6.5
4.2 3.6 4.2 3.9 3.8 4.9 3.5 3.4 3.8 3.1 3.6 3.6 4.2 3.8 5.0
Mean Minimum Maximum S.D.
11.2 9.6 14.1 1.3
79.3 76.3 81.4 1.6
75.8 71.2 78.8 2.1
48.9 44.5 53.1 2.9
45.7 41.8 50.9 2.6
9.3 6.3 12.8 1.7
6.8 5.2 8.1 0.9
3.9 3.1 5.0 0.5
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(Nakashima and érskov, 1990; Warly et al., 1992) and Malaysia (Vadiveloo and Phang, 1996), and 18.6% in Californian varieties (Abou-El-Enin et al., 1999). The total silica (SiO2) content of rice straw averaged 6.8%. These values correspond to those obtained in Malaysian varieties (Vadiveloo and Phang, 1996), but were lower than those from the majority of rice straw samples collected throughout the production areas (Balasta et al., 1989; Doyle and Chanpongsang, 1990; Rahal et al., 1997; Abou-El-Enin et al., 1999). As silica uptake from soil and content in plant depends on its concentration in soil solution (Balasta et al., 1989), the low silica content in our study may be due to a low silica content in soil from the Camargue region. There was a high correlation (r 0:80, P < 0:001) between SiO2 and ash contents. The contribution of SiO2 to ash content was 60.9%, which was lower than the 72.3% reported for US varieties (Abou-El-Enin et al., 1999). Therefore, low ash content in our study is obviously due to low silica content. The NDF and ADF ranged from 76.3 and 44.5% for rice straw L to 81.4 and 53.1% for straw J. The NDF range and that for ash-free NDF were similar to other ranges reported from Australia (Doyle and Chanpongsang, 1990; Doyle and Panday, 1990), but were higher than those reported in US (Abou-El-Enin et al., 1999), Malaysian (Vadiveloo and Phang, 1996), Japanese (Nakashima and érskov, 1990; Warly et al., 1992) or Indian (Rahal et al., 1997) rice straw. Ash in NDF essentially originates from soil and biogenic minerals (Van Soest et al., 1991), because of their insolubility in neutral detergent solution (NDS). Ash content in NDF can be considerable (Crocker et al., 1998) and is especially important in rice straw: the difference between NDF and ash-free NDF was 7.8% units for rice straw (Crocker et al., 1998) whereas it averaged 1% units for ®ve other samples (alfalfa hay, beet pulp, oat hay, soybean hulls, whole cottonseed). On average, ash-free NDF and ADF were, respectively 3.5 and 3.2% units lower than NDF and ADF, showing less soil contamination than previous data. Ash contamination was not uniform, from 1.9 to 6.3% in NDF and from 2.9 to 10.0% in ADF. Variation in ash contamination could be due to the presence of water from rain several days prior to harvesting the straw, which could have contaminated stems and broken leaves to varying degrees with silica from soil. Lignin content ranged from 6.3 to 12.9% with a mean value of 9.3%. These lignin contents are unusually high since literature data for rice straw showed lignin content < 7% in dry matter, whatever the geographical origin (Fall et al., 1987; Doyle and Chanpongsang, 1990; Doyle and Chanpongsang, 1990; Warly et al., 1992; Warly et al., 1992; Vadiveloo and Phang, 1996; Vadiveloo and Phang, 1996; Abou-El-Enin et al., 1999; Abou-El-Enin et al., 1999). A negative correlation (r 0:48, P < 0:01) was noted between silica and lignin content in 49 varieties of forages (Van Soest and Jones, 1968). Such a relationship was not found in this work. Moreover, we cannot provide any physiological explanation for this relationship, except that ash, especially silica incrustation, may act like lignin components (Van Soest and Jones, 1968; Raven, 1983) by blocking the cell wall structure of rice straw and rendering it impermeable. Consequently, lignin synthesis could be diminished in the cells. Silica and lignins react as two components of a balanced system which may play a role in the control of the end of cell wall expansion. More studies are needed to verify this hypothesis. CP content averaged 3.9%. These CP contents were similar to data recorded from previous works (Fall et al., 1987; Nakashima and érskov, 1990; Vadiveloo and Phang, 1996; Abou-El-Enin et al., 1999) which averaged 4.1%.
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Table 3 Proportion of morphological fractions in rice straw samples (% whole straw) and ratio of total leaves to stems. Straw identification
Chaff
Stem
Leaf blade
Leaf sheath
Miscellaneous
Total leaves
Leaves/stem
A B C D E F G H I J K L M N O
7.2 8.2 6.4 9.8 8.8 6.8 7.4 8.7 4.2 7.2 5.6 9.2 11.5 3.7 7.6
17.5 30.7 22.2 19.8 31.2 25.9 24.0 25.1 21.1 25.1 21.9 18.1 20.1 22.6 15.2
39.0 24.6 32.0 37.3 18.0 21.2 31.5 30.4 37.9 36.3 38.4 35.4 35.0 34.7 38.9
35.7 35.5 37.9 32.3 37.6 44.0 36.5 34.8 35.5 29.6 33.4 36.6 33.0 37.5 36.7
0.64 1.12 1.56 0.55 3.09 2.08 0.48 0.71 1.16 1.81 0.49 0.88 0.43 1.79 1.30
75.4 61.2 71.4 70.6 59.2 67.3 68.6 67.0 73.9 67.7 71.9 73.6 68.4 73.5 77.1
4.3 2.0 3.2 3.5 1.9 2.7 2.9 2.8 3.4 2.7 3.2 4.1 3.4 3.2 5.0
Mean Minimum Maximum S.D.
7.5 3.7 11.5 2.0
22.7 15.2 31.2 4.5
32.7 18.0 39.0 6.6
35.8 29.6 44.0 3.2
1.21 0.43 3.09 0.75
69.8 59.2 77.1 5.0
3.2 1.9 5.0 0.8
3.2. Morphological fractions in rice straw samples Morphological composition of rice straw samples is given in Table 3. There was considerable variability. Stems (nodes internodes) and leaves varied respectively from 15.2 for straw O to 31.2% for E, and from 59.2 for E to 77.1% for A. There were much more leaves than stem, by weight, in all rice straw samples. This trend was especially found in rice straw varieties (Bainton et al., 1987; Walli et al., 1988; Balasta et al., 1989; Doyle and Chanpongsang, 1990; Nakashima and érskov, 1990; Vadiveloo and Phang, 1996), whereas in other straws like wheat (Wales et al., 1990; Flachowsky et al., 1991), oat, barley, triticale (Flachowsky et al., 1991), sorghum or milo (Fall et al., 1987), stem contribution to whole straw was always superior to that of leaves. Chaff content ranged from 3.7 for straw N, to 11.5% in M. The variation depends on the presence or not of seeds in the chaff and on the quantity of chaff itself. The mean contribution of leaf sheaths (35.8) and blades (32.4%) to whole straw were similar in our study, similar to the ®ndings of Vadiveloo and Phang (1996) and unlike those of Doyle and Chanpongsang (1990) where leaf sheath content (mean 33.5%) was similar or higher than blade content (29.6 and 17.0%, respectively). This may be attributed to sunshine period and humidity of respective locations: when sunshine diminished, the leaf area may have increased, probably by increasing leaf blade surface area, to increase the surface exposed to light. Stem length, i.e. plant length, could also be a factor interrelated with leaf content: a negative (r 0:59) and positive (r 0:59) relation between stem length and, leaf and stem contents respectively, was observed in barley straw (Cocks and Thomson, 1988). The same
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relationships were found between rice straw height (Table 1) and leaf proportion (r 0:33) or stem proportion (r 0:38) in this study, but they were not signi®cant. A signi®cant correlation was found between leaf blade and sheath fractions (r 0:56, P < 0:05). The respective contribution of blades, sheaths and miscellaneous fractions to total leaves was variable among straw samples. A couple of straw samples (E and F) showed a low contribution of blades to total leaves which averaged 30.92% and three others (D, J and K) had the highest contribution averaging 53.3%. The presence of brittle parts (miscellaneous fraction) was low (mean 1.3%) in whole straw. It represented up to 5.2% of total leaves for straw E. When the miscellaneous fraction was high, the corresponding straw was more susceptible to brittleness than other. The miscellaneous proportion was negatively related (r 0:65, P < 0:01) to leaf blade fraction and not related (P 0:11) to leaf sheaths or total leaves. Therefore, the stem to leaf blade ratio should have a potential as an indicator of the susceptibility of straws to break easily, as well as grinding energy which is a measure of the resistance to particle size reduction. Negative relationships were found between grinding energy and intake (Pearce et al., 1998) in rice and wheat straws. A high stem to leaf blade ratio would therefore be related to low grinding energy of straw and to high intake. 3.3. Whole straw degradation after 24 and 72 h of rumen incubation Data for in sacco degradation of whole straws are given in Table 4. OM degradation values were close to that of DM. This low difference between both values could be due to a Table 4 In sacco degradation (%) of dry matter (DM) and organic matter (OM) of straw samples at 24 and 72 h of incubation Straw identification
DM
OM
24 h
72 h
24 h
72 h
A B C D E F G H I J K L M N O
31.4 29.0 31.0 32.3 26.8 26.6 29.9 30.7 29.4 28.0 36.3 35.3 30.8 30.1 28.8
51.4 48.9 50.4 52.7 43.7 43.6 49.7 51.1 51.1 50.0 56.4 57.6 48.7 50.4 48.7
30.9 24.4 28.2 30.5 25.0 23.6 28.4 31.3 29.2 25.4 35.6 35.6 29.4 29.0 28.3
51.7 47.0 49.4 52.8 42.7 42.2 49.4 52.3 51.6 49.0 57.0 58.7 48.0 51.3 49.3
Mean Minimum Maximum S.D.
30.4 26.6 36.3 2.7
50.3 43.6 57.6 3.7
29.0 23.6 35.6 3.6
50.2 42.2 58.7 4.4
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high ash loss from the bags during incubation. The variation between maximum and minimum values was 10% units for DM degraded at 24 h, to 17% units for OM degraded at 72 h. Differences between degradation values were more evident for OM than for DM, and for 72 than for 24 h. Degradation at 24 h for DM in rice straw samples was in the range of other reported values: 20.0 (Bae et al., 1997) to 40.8% (Adya et al., 1995). OM degradation at 24 h was lower than published data (Walli et al., 1988; Adya et al., 1995; Wilman et al., 1999), whereas for OM disappearance at 72 h, most of the rice straw samples (see Table 4) were in the range of reported values (49.3 to 61.5%) (Walli et al., 1988; Rahal et al., 1997). Whatever the time of incubation, the ranking of straw samples was equivalent either with DM or OM degradation. Ranking was different between 24 and 72 h, but differences were very small for intermediate samples. Moreover, the straw with the higher (straws K and L) and lower (straws E, F) DM or OM degradation were the same at both time of incubation. Since these straws samples were incubated in similar microbial environment, it can be suggested that the observed variations in straw degradation were related to their chemical and/or physical properties. 3.4. Relationship between degradation, and morphological and chemical composition of rice straw samples In the present work, all rice straw samples were grown under similar soil and identical agronomic conditions. Thus, the large variability in ruminal degradation between samples may be related to their genetic characteristics, re¯ected by a large variability in their morphological and chemical composition. We thus assessed the relationships between degradation, morphological and chemical composition of rice straw samples, by PCA. The ®rst two axes explained 64 to 69% of the variance for the 4 PCA. The ®rst axis discriminated the extent of degradation together with morphological and chemical parameters. Result for PCA 1 is given in Fig. 1. Concerning morphological variables, degradation was positively related to the proportion of total leaves (PCA 3 and 4), negatively related to the stem proportion and not related to chaff proportion. For leaves, degradation was positively related to leaf blade proportion and not related to leaf sheath (PCA 1 and 2). In agreement with these results, Flachowsky et al. (1991) reported that for 51 varieties of cereal straw (oat, barley, rye, wheat, triticale), the DM degradation after 48 h incubation in the rumen of sheep was negatively related to internode proportion and positively related to leaf proportion in whole straw. However, in previous works on degradation of morphological fractions of rice straw, it has been reported that degradability of stems was higher than or similar to that of leaf sheaths or blades, as observed in vitro (Bainton et al., 1986; Vadiveloo, 1995; Vadiveloo, 2000) and of leaves, as observed in sacco (Walli et al., 1988; Nakashima and érskov, 1990), whereas the adverse trend was observed for other Poaceae (Flachowsky et al., 1991). Our results suggest that the relationship between total leaves and degradation may largely depend on the blade proportion, which varies widely from 30 to 54% of total leaves in our study. This may explain the differences in the relationship between degradation and leaf proportion between experiments reported, as blade and sheath were not differentiated in some of them.
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Fig. 1. Representation on factorial circle of the first two axes, for principal component analysis 1 (PCA 1) of rice straw variability. 24: OM degraded at 24 h; 72: OM degraded at 72 h; circles: morphological factors; squares: chemical factors; LB: leaf blade; LS: leaf sheath; S: stem; Ch: chaff; Si: SiO2; CP: crude protein; H: hemicelluloses; Ce: cellulose; L: lignins.
Concerning chemical variables, degradation was positively related to hemicelluloses, whereas increasing NDF, cellulose and lignin tended to decrease degradation. The same trend was observed when ®bers (PCA 1 and 3) or ash-free ®bers (PCA 2 and 4) were taken into account. These ®ndings are in agreement with Tripathi et al. (1996) showing negative correlation between in sacco OM degradation and NDF (r 0:25), cellulose (r 0:10) and lignin (r 0:77). Also, Fall et al. (1998) reported that both NDF and ADF were negatively related to DM degradability of various varieties of cereal straw including rice. In our study, the linear relationships between cell wall components and whole straw OM degradation were stronger with ADF than with NDF (r 0:79 versus 0.58 at 24 h and 0.69 versus 0.43 at 72 h, for ADF versus NDF, respectively). This is in line with Fall et al. (1998) who reported that ADF was better than NDF for prediction of DM degradability of straw varieties. It should be emphasized that compared to NDF, ash-free NDF is poorly related to degradation (r 0:34 and 0.21 at 24 h and 72 h, respectively). Since the difference between NDF and ash-free NDF is attributed to ash from soil (Crocker et al., 1998), it may be suggested that ash from soil induced a depressive effect on degradation. This is not consistent with results given by direct measurements of ash and SiO2, which showed no negative relationship with degradation, whereas most previous studies focused on the effect of SiO2 on straw degradation reported a negative effect (Shimojo and Goto, 1989; Balasta et al., 1989; Fall et al., 1998). As discussed above, it may be due to the low content of SiO2 of straw samples in our study compared to samples from other geographic provenance (Doyle and Chanpongsang, 1990; Rahal et al., 1997; Abou-El-Enin et al., 1999). Since leaf blade proportion and hemicelluloses appeared to be the main morphological and chemical factors related to degradation, the linear relationships between leaf blade and/or
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Table 5 Linear relationships between OM degraded (%) and leaf blade proportion (%) and hemicellulose content (%) in rice straw samplesa Slopes
Intercept OM degraded 24 h
OM degraded 72 h
Leaf blade
17.58 (3.83)*** 17.79 (11.20) NSb 11.90 (12.08) NS ***
33.86 (4.16) 5.35 (14.66) NS 7.22 (14.19) NS
0.349 (0.115)** 0.149 (0.125) NS 0.498 (0.125)** 0.317 (0.147)
Hemicelluloses
r2
1.538 (0.368)** 1.185 (0.468)*
0.416 0.574 0.619
1.826 (0.482)** 1.071 (0.550)
0.550 0.525 0.658
a
Values in parentheses are standard error of estimates. Non-significant. P < 0:10. * P < 0:05. ** P < 0:01. *** P < 0:001. b
hemicelluloses and OM degradation were calculated (Table 5). The variability in degradation between straw samples at 24 h and 72 h was partly explained by leaf blade alone (42 and 55%, respectively) and hemicelluloses alone (57 and 53%, respectively). The model was improved when both morphological and chemical variables were included, allowing more than 60% of variability in degradation between straw samples to be explained (Fig. 2).
Fig. 2. Correlation between calculated and measured values for organic matter degradation after 24 (~) and 72 h ( ) incubation. Calculated values were obtained with the following equations: OM degraded at 24 h % 11:30 0:149 Leaf blade 1:185 Hemicelluloses; OM degraded at 72 h % 7:22 0:317 Leaf blade 1:071 Hemicelluloses. Closed line: X Y.
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4. Conclusion This study provides new information on the relationships between composition and ruminal degradation of rice straw varieties. Fractionation of whole straw samples showed that the variability in whole plant degradation was highly related to leaf blade proportions, which appeared to be better than total leaves as a criterion for ruminal degradability. Equations are proposed to assess the susceptibility of rice straw samples to ruminal degradation, according to chemical (hemicelluloses) and/or morphological (leaf blade) variables. No effect of SiO2 on straw degradation has been evidenced, but this may be related to the low SiO2 contents of straw samples, due to geographical and agronomic conditions. Acknowledgements The authors wish to thank D. Thomas for help in straw harvesting and C. Bardoux, M. Pezant and F. Duchier for fractionation of straw samples. They are grateful to M. Jamot for preparation of nylon bags and D. Roux for animal care and help in nylon bag management.
References Abou-El-Enin, O.H., Fadel, J.G., Mackill, D.J., 1999. Differences in chemical composition and fibre digestion of rice straw with, and without anhydrous ammonia from 53 rice varieties. Anim. Feed Sci. Technol. 79, 129±136. Adya, M., Sareen, V.K., Singh, S., 1995. Effect of hydrothermal treatment of rice straw on its composition and in sacco digestibility and in vitro fermentation by rumen microorganisms. Acta Vet. Hung. 43, 179±190. AOAC, 1984. Official Methods of Analysis. 14th Edition, AOAC, Arlington, VA. Bae, H.D., McAllister, T.A., Kokko, E.G., Leggett, F.L., Yanke, L.J., Jakober, K.D., Ha, J.K., Shin, H.T., Cheng, K.-J., 1997. Effect of silica on the colonization of rice straw by ruminal bacteria. Anim. Feed Sci. Technol. 65, 165±181. Bainton, S.J., Plumb, V.E., Capper, B.S., Juliano, B.O., 1987. Botanical composition, chemical analysis and cellulase solubility of rice straw from different varieties. In: Proceedings of the British Society of Animal Production. Anim. Prod. 44, 481 (Abstract). Bainton, S.J., Plumb, V.E., Drake, M.D., Juliano, B.O., Capper, B.S., 1986. Effect of physiological and morphological characteristics on in vitro cellulase solubility of different varieties of rice straw. In: Dixon, R.M., (Ed.), Ruminant Feeding Systems Utilizing Fibrous Agricultural Residues. IDP, Canberra, pp. 115±120. Balasta, M.L.F.C., Perez, C.M., Juliano, B.O., Villareal, C.P., Lott, J.N.A., Roxas, D.B., 1989. Effects of silica level on some properties of Oryza sativa straw and hull. Can. J. Bot. 67, 2356±2363. Cocks, P.S., Thomson, E.F., 1988. Increasing feed resources for small ruminants in the Mediterranean basin. In: Thomson, E.F., Thomson, F.S. (Eds.), Increasing Small Ruminant Productivity in Semi-Arid Areas. ICARDA, Aleppo, Syria. pp. 51±66. Crocker, L.M., DePeters, E.J., Fadel, J.G., Essex, S.E., Perez-Monti, H., Taylor, S.J., 1998. Ash content of detergent fibers in feeds, digesta, and feces and its relevance in fiber digestibility calculations. J. Dairy Sci. 81, 1010±1014. Doyle, P.T., Chanpongsang, S., 1990. The feeding value of cereal straws for sheep. Part II. Rice straws. Anim. Feed Sci. Technol. 29, 15±28. Doyle, P.T., Panday, S.B., 1990. The feeding value of cereal straws for sheep. Part III. Supplementation with minerals or minerals and urea. Anim. Feed Sci. Technol. 29, 29±43.
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Erickson, D.O., Meyer, D.W., Foster, A.E., 1982. The effect of genotypes on the feed value of barley straws. J. Anim. Sci. 55, 1015±1026. Fall, S.T., CisseÂ, M., Ditaroh, D., Richard, D., Ndiaye, N.S., Diaw, B., 1998. In vivo nutrient digestibility in sheep, and rumen dry matter degradability in cattle fed crop by-product based diets. J. Anim. Feed Sci. 7, 171±185. Fall, S.T., Guerin, H., Sall, C., Mbaye, N., 1987. Les Pailles le CeÂreÂales dans de SysteÁme d'Alimentation des Ruminants du SeÂneÂgal. LNRV, ISRA, Dakar±Hann, SeÂneÂgal. Flachowsky, G., Tiroke, K., Schein, G., 1991. Botanical fractions of straw of 51 cereal varieties and in sacco degradability of various fractions. Anim. Feed Sci. Technol. 34, 279±289. Horwitz, 1960. Official Methods of Analysis of the Association of Official Agricultural Chemists, 4th Edition, AOAC, Washington, DC. Mathison, G.W., Soofi-Siwash, R., Okine, E.K., Helm, J., Juskiw, P., 1999. Factors influencing composition and ruminal degradability of barley straw. Can. J. Anim. Sci. 79, 343±351. Mawuenyegah, P.O., Shem, M.N., Warly, L., Fujihara, T., 1997. Effect of supplementary feeding with protein and energy on digestion and rumination behaviour of sheep consuming straw diets. J. Agric. Sci. Camb. 129, 479±484. Nakashima, Y., érskov, E.R., 1990. Rumen degradation of straw. Part 9. Effect of cellulase and ammonia treatment on different varieties of rice straws and their botanical fractions. Anim. Prod. 50, 309±317. Pearce, G.R., Lee, J.A., Simpson, R.J., Doyle, P.T., 1998. Sources of variation in the nutritive value of wheat and rice straws. In: Reed, J.D., Capper, B.S. (Eds.), Plant Breeding and the Nutritive Value of Crop Residues. pp. 195±231. Rahal, A., Singh, A., Singh, M., 1997. Effect of urea treatment and diet composition on, and prediction of nutritive value of rice straw of different cultivars. Anim. Feed Sci. Technol. 68, 165±182. Raven, J.A., 1983. The transport and function of silicon in plants. Biol. Rev. 58, 179±207. Reddy, D.V., 1997. The effect of supplementation of legume straws on utilisation of rice straw±poultry droppings±rice bran±fish meal based diet in buffaloes. Anim. Feed Sci. Technol. 69, 305±314. SAS, 1989. SAS/STAT User's Guide 5, Release 6.03. SAS Inst. Inc., Cary, NC. Shimojo, M., Goto, I., 1989. Effect of sodium silicate on forage digestion with rumen fluid of goats or cellulase using culture solutions adjusted for pH. Anim. Feed Sci. Technol. 24, 173±177. Tripathi, M.K., Tiwari, A.D., Singh, M., Chandra, A., Mishra, A.S., 1996. Rumen nutrient degradation pattern and their correlation in two varieties of rice straw. Indian J. Anim. Sci. 66, 1046±1051. Vadiveloo, J., 1995. Factors contributing to varietal differences in the nutritive value of rice straw. Anim. Feed Sci. Technol. 54, 45±53. Vadiveloo, J., 2000. Nutritional properties of the leaf and stem of rice straw. Anim. Feed Sci. Technol. 83, 57±65. Vadiveloo, J., Phang, O.C., 1996. Differences in the nutritive value of two rice straw varieties as influenced by season and location. Anim. Feed Sci. Technol. 61, 247±258. Van Soest, P.J., Jones, L.H.P., 1968. Effect of silica in forages upon digestibility. J. Dairy Sci. 51, 1644±1648. Van Soest, P.J., Robertson, J.B., Lewis, B.A., 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74, 3583±3597. Wales, W.J., Doyle, P.T., Pearce, G.R., 1990. The feeding value of cereal straws for sheep. Part I. Wheat straws. Anim. Feed Sci. Technol. 29, 1±14. Walli, T.K., érskov, E.R., Bhargava, P.K., 1988. Rumen degradation of straw. Part 3. Botanical fractions of two rice straw varieties and effects of ammonia treatment. Anim. Prod. 46, 347±352. Wanapat, M., Sommart, K., Saardrak, K., 1996. Cottonseed meal supplementation of dairy cattle fed rice straw. Liv. Res. Rural Dev. 8. Warly, L., Matsui, T., Harumoto, T., Fujihara, T., 1992. Study on the utilization of rice straw by sheep. Part 1. The effect of soybean meal supplementation on the voluntary intake of rice straw and ruminal fermentation. Asian±Aus. J. Anim. Sci. 5, 687±693. Williams, B.A., Chuzaemi, S., van Bruchem, J., Boer, H., Tamminga, S., 1996. A comparison of ten rice-straw varieties grown at two different altitudes during a wet and a dry season, using the in vitro cumulative gas production technique. Anim. Feed Sci. Technol. 57, 183±194. Wilman, D., Wen, L., Qin, H., Ji, Y., 1999. Intake and digestibility of diets derived from stovers and straws compared with lucerne hay and sweet potato haulm. J. Agric. Sci. Camb. 132, 207±213.
In sacco degradability, chemical and morphological composition of 15 varieties of European rice straw Ahoefa Agbagla-Dohnania, Pierre NozieÁrea,*, Guy CleÂmentb, Michel Doreaua a
Equipe Digestion et Absorption des Nutriments, Unite de Recherches sur les Herbivores (URH), INRA site de Theix, 63122 St. GeneÁs Champanelle, France b CIRAD-CA, Montpellier, France Received 9 March 2001; received in revised form 7 August 2001; accepted 29 August 2001
Abstract The aim of this study was to evaluate the variability in chemical and morphological variables of European rice straw varieties and to relate these variations to changes in in sacco degradation. Fifteen rice straw varieties were analyzed for their chemical and morphological compositions. Ground (2 mm) straw was incubated in the rumen of three ruminally cannulated cows for 24 and 72 h for in sacco degradability measurements. Results were analyzed by principal component analysis (PCA) and equations are proposed for degradation of rice straw in the rumen according to morphological and chemical variables. Both chemical and morphological characteristics presented great variability. Mean values, on a dry matter (DM) basis (%), for ash, silica, crude protein (CP), ash-free neutral detergent ®ber (NDF), ash-free acid detergent ®ber (ADF), and acid detergent lignin (ADL), were 11.2, 6.8, 3.9, 75.8, 45.7 and 9.3 respectively. Mean values, on a DM basis (%), for stem (internodes nodes), leaf blade, leaf sheath and chaff were 22.7, 32.7, 35.8 and 7.5 respectively. Variation in the in sacco degradation (%) of DM and organic matter (OM) was observed among straw varieties at 24 and 72 h: 30.4 (26.6±36.3) and 50.3 (43.6±57.6) for DM degradation; 29.0 (23.6±35.6) and 50.2 (42.2±58.7) for OM. The principal component analysis discriminated degradation parameters with botanical and chemical parameters. Degradation (%) was positively related to total leaves and leaf blade fractions and hemicelluloses, and negatively related to stem fraction, NDF, cellulose and lignin. Cumulative equation with both leaf blades (morphological variable) and hemicelluloses (chemical variable) explained 62 and 66% of variation in OM degradation at 24 and 72 h, respectively. # 2001 Published by Elsevier Science B.V. Keywords: Rice straw; Cell wall components; Morphological fractions; In sacco degradation *
Corresponding author. Tel.: 33-473-624-686; fax: 33-473-624-273. E-mail address: [email protected] (P. NozieÁre). 0377-8401/01/$ ± see front matter # 2001 Published by Elsevier Science B.V. PII: S 0 3 7 7 - 8 4 0 1 ( 0 1 ) 0 0 2 9 6 - 6
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1. Introduction Rice is principally produced for human consumption and a large amount of straw is left in the ®eld. Rice straw constitutes a source of carbohydrates for ruminants in countries where it is produced. However, it has high lignin and low nitrogen contents which in combination are responsible for its low nutritive value. Many attempts have been made to improve its nutritive value, especially by chemical treatments (Rahal et al., 1997; Abou-ElEnin et al., 1999; Vadiveloo, 2000). Supplementing rice straw with concentrates (Wanapat et al., 1996; Mawuenyegah et al., 1997), with by-products such as niebe or blackgram straw (Reddy, 1997) showed some ef®ciency for animal feeding. Researchers have shown that selection could improve the nutritive value of rice (Bainton et al., 1986; Vadiveloo, 1995) and other cereal (Erickson et al., 1982; Flachowsky et al., 1991; Mathison et al., 1999) straws without negatively affecting their agronomic characteristics. Nevertheless, variability is an important subject that must be discussed when applying these varying approaches. Rice straw from Asia and United States has shown great variability in chemical composition (Vadiveloo, 1995; Abou-El-Enin et al., 1999), proportion of morphological fractions (Vadiveloo, 1995) and digestibility as estimated by in vitro (Vadiveloo, 1995; Williams et al., 1996) or in sacco (Nakashima and érskov, 1990; Rahal et al., 1997; Abou-El-Enin et al., 1999) measurements, but less is known about variability in European varieties. In this work, the relationships between degradability and chemical and/or morphological characteristics of 15 European varieties of rice straw have been studied. These straw varieties were grown under identical agronomic conditions to avoid the interference of environment and agronomic practices. Chemical composition and morphological fractions were measured and in sacco degradation was assessed. 2. Materials and methods 2.1. Straws Fifteen rice straw varieties (lettered A to O) were collected at maturity after grain harvesting in November 1999, from the CIRAD experimental rice®eld station, Mas d'Adrien, Camargue, France. This location is within the Beaucaire plain, between the little RhoÃne and the Mediterranean coast. The varieties were from a selection trial and were grown under similar agronomic conditions on the same ®eld (3 ha), in plots (500 m2) separated by bunds. The soils of this region are of sandy alluvial type, pH > 7. Flooding and sowing were performed on the 12 and 13 March. Fertilizer (urea) was applied at midtillering (17 June) and at the initiation of panicle (6 or 16 July). Final draining of the rice®eld occurred on the 20 September. The names and some agronomic characteristics of these straw samples are given in Table 1. Straw samples were hand-harvested 10 cm above the ground. The quantity harvested was 10 kg for each variety. The straw samples were laid out in a ventilated barn and periodically turned to prevent fermentation. One month after harvest, most of the moisture having been removed (no moisture to the touch) by air-drying, the straw was oven-dried at 40 8C for 72 h.
Straw identification
Name, Genotype
Origin
Pilosity
Height (cm)
Grain type
Parasitism
A B C D E F G H I J K L M N O
3488 A 301±F1 ARIETE CRISTALAVA H1 MIARA±BW DEDALO MIARA±S DELTASIENNE MIARA±I MOLO ESTRELA±H (PYGMALION IRAT 122) PYGMALION±A1 RINGO MIARA±AC SP 81 SP 91 SP 92 SP 93 ST 25/87 MIARA±R THAIÈBONNET THAIÈBONNET MIARA±AF
France Italy France France France France France France France France France France France United States France
Smooth Villous Smooth Villous Villous Less villous Less villous Villous Smooth Smooth Smooth Smooth Less villous Smooth Smooth
70 85 85 80 65 80 80 80 80 80 65 65 80 75 60
Long Long Long Long Long Long Long Long Long Long Long Long Long Long Long
No S Chilo suppressalis No MS Chilo suppressalis MR Fusarium roseum S Sclerotium sp. No MS Chilo suppressalis No No No No No MR Chilo suppressalis No
a
slender large slender slender large slender slender large slender large slender slender slender slender slender
No: no parasitism in straw. MR, MS, S, indicate the degree of sensibility to parasitism: moderate resistant, moderate susceptible, susceptible.
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Table 1 Name, origin, height, grain type and susceptibility to parasitism of rice strawsa
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2.2. Morphological analyses of straw samples The relative proportion by weight of leaf blade, leaf sheath, stem and chaff in approximately 200 g of whole straw was estimated in quadruplicate. Leaves were removed from internodes by cutting the stems above the nodes. Nodes plus internodes were pooled to constitute the stem fraction. Leaf sheath and leaf blade were separated. A miscellaneous fraction made of brittle parts (mainly leaf particles) was also determined. Total leaf proportion was calculated as the sum of leaf sheath, leaf blade and miscellaneous fraction. Part of the remaining straw was milled to pass through a 2 mm sieve for chemical analyses and in sacco studies. 2.3. Chemical analyses The straw samples were analyzed for total ash (550 8C, 6 h), neutral detergent ®ber (NDF), acid detergent ®ber (ADF) and acid detergent lignin (ADL) (Van Soest et al., 1991).1 Ash-free NDF and ADF were calculated from the determination of their ash content (Van Soest et al., 1991). Total silica (SiO2) was determined by the gravimetric method of hydro¯uoric acid evaporation (Horwitz, 1960). Crude protein (CP) content was calculated as N 6:25 from the total N determined by Dumas technique (AOAC, 1984). Analyses for total ash, silica and total N were performed in duplicate, and the others in triplicate. 2.4. In sacco degradation Three dry Holstein cows, average body weight of 805 21 kg, ®tted with permanent rumen cannulas were given a diet of 70% second cut of orchard grass hay and 30% concentrate (barley 43%, beet pulp 40%, soybean meal 10% and molasses 5%). The diet was distributed at a rate of 7 kg DM per day, in two equal meals at 09:00 and 17:00 h. Degradation measurements were made after 4 weeks of adaptation. Thirty dacron bags (Ankom Co, Fairport, NY, USA; pore size: 53 mm and internal dimensions: 5 cm 9 cm) per cow, i.e. 2 bags per feed, were ®lled with 2.5 g of straw and incubated in the rumen of the three cows for 24 and 72 h. The incubation sequence was repeated once. After incubation, the nylon bags were removed from the rumen, immediately rinsed in cold water and frozen. They were then machine-washed until water was clear: 5 cycles of 5 min, with cold water (approximately 10 l per cycle). The washed bags were oven-dried for 48 h at 60 8C and weighed. Residues were analyzed for ash and straw DM and OM disappearance values were calculated as the difference between weights before and after incubation of samples. 2.5. Statistical analyses Principal component analysis (PCA) of the data on degradation (OM degraded at 24 and 72 h), chemical composition (lignin, hemicelluloses, cellulose, SiO2, CP, and 1
This publicaton is no longer available. If this procedure was used, give the ``1991'' as the reference and specify procedural changes.
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morphological composition (stems, chaff, leaves), was carried out to quantify the contribution of each variable to the variation in degradation pattern of the straw. Four analyses were carried out, according to the variables: (1) lignin (ADL), hemicelluloses (being estimated from NDF and ADF), cellulose (being estimated from ADF and ADL), leaf blade and leaf sheath (PCA 1), (2) lignin, hemicelluloses (being estimated from ash-free NDF and ash-free ADF), cellulose (being estimated from ash-free ADF and ADL), leaf blade and leaf sheath (PCA 2), (3) lignin, hemicelluloses, cellulose (estimated from NDF, ADF and ADL), and total leaves (PCA 3) and (4) lignin, hemicelluloses, cellulose (estimated from ash-free ®ber residues and ADL), and total leaves (PCA 4). Single and multiple linear relationships between degradation and chemical and/or botanical parameters were calculated. All analyses were performed using SAS (1989). 3. Results and discussion 3.1. Chemical composition Straw composition, on a dry matter basis, was variable as shown in Table 2. Ash content of rice straw samples ranged from 9.6 for straw I to 14.1% for straw B. These values were very low compared to reported ash content in rice straw samples which averaged 14.1% in Philippine varieties (Bainton et al., 1987; Balasta et al., 1989), 16,6% in Asian varieties from other countries: India (Walli et al., 1988; Adya et al., 1995; Rahal et al., 1997), Japan Table 2 Chemical composition of rice straw samples (A to O), on a dry matter basis (%) Straw identification
Ash
NDF
Ash-free NDF
ADF
Ash-free ADF
ADL
Silica
CP
A B C D E F G H I J K L M N O
11.7 14.1 13.8 11.0 9.8 12.2 11.8 10.4 9.6 10.8 11.0 10.7 11.0 10.3 10.5
79.6 80.8 79.3 79.0 80.2 79.9 79.9 81.3 79.7 81.4 77.8 76.3 76.6 79.7 77.2
76.4 76.9 72.8 76.7 76.9 74.5 76.3 78.6 77.6 78.8 75.3 71.2 73.5 76.6 74.5
48.4 52.3 50.2 48.6 50.6 52.9 48.0 51.5 47.1 53.1 44.5 44.5 47.0 48.5 45.8
43.5 46.4 45.4 45.9 48.1 48.7 46.4 47.4 44.8 50.9 41.8 42.0 45.5 46.3 42.2
9.5 10.0 11.6 8.4 10.0 12.9 7.1 9.1 9.1 8.6 6.3 9.1 7.5 9.9 10.2
7.5 8.1 7.9 7.0 5.6 7.2 7.7 7.8 5.2 6.3 6.7 6.3 6.6 6.1 6.5
4.2 3.6 4.2 3.9 3.8 4.9 3.5 3.4 3.8 3.1 3.6 3.6 4.2 3.8 5.0
Mean Minimum Maximum S.D.
11.2 9.6 14.1 1.3
79.3 76.3 81.4 1.6
75.8 71.2 78.8 2.1
48.9 44.5 53.1 2.9
45.7 41.8 50.9 2.6
9.3 6.3 12.8 1.7
6.8 5.2 8.1 0.9
3.9 3.1 5.0 0.5
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(Nakashima and érskov, 1990; Warly et al., 1992) and Malaysia (Vadiveloo and Phang, 1996), and 18.6% in Californian varieties (Abou-El-Enin et al., 1999). The total silica (SiO2) content of rice straw averaged 6.8%. These values correspond to those obtained in Malaysian varieties (Vadiveloo and Phang, 1996), but were lower than those from the majority of rice straw samples collected throughout the production areas (Balasta et al., 1989; Doyle and Chanpongsang, 1990; Rahal et al., 1997; Abou-El-Enin et al., 1999). As silica uptake from soil and content in plant depends on its concentration in soil solution (Balasta et al., 1989), the low silica content in our study may be due to a low silica content in soil from the Camargue region. There was a high correlation (r 0:80, P < 0:001) between SiO2 and ash contents. The contribution of SiO2 to ash content was 60.9%, which was lower than the 72.3% reported for US varieties (Abou-El-Enin et al., 1999). Therefore, low ash content in our study is obviously due to low silica content. The NDF and ADF ranged from 76.3 and 44.5% for rice straw L to 81.4 and 53.1% for straw J. The NDF range and that for ash-free NDF were similar to other ranges reported from Australia (Doyle and Chanpongsang, 1990; Doyle and Panday, 1990), but were higher than those reported in US (Abou-El-Enin et al., 1999), Malaysian (Vadiveloo and Phang, 1996), Japanese (Nakashima and érskov, 1990; Warly et al., 1992) or Indian (Rahal et al., 1997) rice straw. Ash in NDF essentially originates from soil and biogenic minerals (Van Soest et al., 1991), because of their insolubility in neutral detergent solution (NDS). Ash content in NDF can be considerable (Crocker et al., 1998) and is especially important in rice straw: the difference between NDF and ash-free NDF was 7.8% units for rice straw (Crocker et al., 1998) whereas it averaged 1% units for ®ve other samples (alfalfa hay, beet pulp, oat hay, soybean hulls, whole cottonseed). On average, ash-free NDF and ADF were, respectively 3.5 and 3.2% units lower than NDF and ADF, showing less soil contamination than previous data. Ash contamination was not uniform, from 1.9 to 6.3% in NDF and from 2.9 to 10.0% in ADF. Variation in ash contamination could be due to the presence of water from rain several days prior to harvesting the straw, which could have contaminated stems and broken leaves to varying degrees with silica from soil. Lignin content ranged from 6.3 to 12.9% with a mean value of 9.3%. These lignin contents are unusually high since literature data for rice straw showed lignin content < 7% in dry matter, whatever the geographical origin (Fall et al., 1987; Doyle and Chanpongsang, 1990; Doyle and Chanpongsang, 1990; Warly et al., 1992; Warly et al., 1992; Vadiveloo and Phang, 1996; Vadiveloo and Phang, 1996; Abou-El-Enin et al., 1999; Abou-El-Enin et al., 1999). A negative correlation (r 0:48, P < 0:01) was noted between silica and lignin content in 49 varieties of forages (Van Soest and Jones, 1968). Such a relationship was not found in this work. Moreover, we cannot provide any physiological explanation for this relationship, except that ash, especially silica incrustation, may act like lignin components (Van Soest and Jones, 1968; Raven, 1983) by blocking the cell wall structure of rice straw and rendering it impermeable. Consequently, lignin synthesis could be diminished in the cells. Silica and lignins react as two components of a balanced system which may play a role in the control of the end of cell wall expansion. More studies are needed to verify this hypothesis. CP content averaged 3.9%. These CP contents were similar to data recorded from previous works (Fall et al., 1987; Nakashima and érskov, 1990; Vadiveloo and Phang, 1996; Abou-El-Enin et al., 1999) which averaged 4.1%.
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Table 3 Proportion of morphological fractions in rice straw samples (% whole straw) and ratio of total leaves to stems. Straw identification
Chaff
Stem
Leaf blade
Leaf sheath
Miscellaneous
Total leaves
Leaves/stem
A B C D E F G H I J K L M N O
7.2 8.2 6.4 9.8 8.8 6.8 7.4 8.7 4.2 7.2 5.6 9.2 11.5 3.7 7.6
17.5 30.7 22.2 19.8 31.2 25.9 24.0 25.1 21.1 25.1 21.9 18.1 20.1 22.6 15.2
39.0 24.6 32.0 37.3 18.0 21.2 31.5 30.4 37.9 36.3 38.4 35.4 35.0 34.7 38.9
35.7 35.5 37.9 32.3 37.6 44.0 36.5 34.8 35.5 29.6 33.4 36.6 33.0 37.5 36.7
0.64 1.12 1.56 0.55 3.09 2.08 0.48 0.71 1.16 1.81 0.49 0.88 0.43 1.79 1.30
75.4 61.2 71.4 70.6 59.2 67.3 68.6 67.0 73.9 67.7 71.9 73.6 68.4 73.5 77.1
4.3 2.0 3.2 3.5 1.9 2.7 2.9 2.8 3.4 2.7 3.2 4.1 3.4 3.2 5.0
Mean Minimum Maximum S.D.
7.5 3.7 11.5 2.0
22.7 15.2 31.2 4.5
32.7 18.0 39.0 6.6
35.8 29.6 44.0 3.2
1.21 0.43 3.09 0.75
69.8 59.2 77.1 5.0
3.2 1.9 5.0 0.8
3.2. Morphological fractions in rice straw samples Morphological composition of rice straw samples is given in Table 3. There was considerable variability. Stems (nodes internodes) and leaves varied respectively from 15.2 for straw O to 31.2% for E, and from 59.2 for E to 77.1% for A. There were much more leaves than stem, by weight, in all rice straw samples. This trend was especially found in rice straw varieties (Bainton et al., 1987; Walli et al., 1988; Balasta et al., 1989; Doyle and Chanpongsang, 1990; Nakashima and érskov, 1990; Vadiveloo and Phang, 1996), whereas in other straws like wheat (Wales et al., 1990; Flachowsky et al., 1991), oat, barley, triticale (Flachowsky et al., 1991), sorghum or milo (Fall et al., 1987), stem contribution to whole straw was always superior to that of leaves. Chaff content ranged from 3.7 for straw N, to 11.5% in M. The variation depends on the presence or not of seeds in the chaff and on the quantity of chaff itself. The mean contribution of leaf sheaths (35.8) and blades (32.4%) to whole straw were similar in our study, similar to the ®ndings of Vadiveloo and Phang (1996) and unlike those of Doyle and Chanpongsang (1990) where leaf sheath content (mean 33.5%) was similar or higher than blade content (29.6 and 17.0%, respectively). This may be attributed to sunshine period and humidity of respective locations: when sunshine diminished, the leaf area may have increased, probably by increasing leaf blade surface area, to increase the surface exposed to light. Stem length, i.e. plant length, could also be a factor interrelated with leaf content: a negative (r 0:59) and positive (r 0:59) relation between stem length and, leaf and stem contents respectively, was observed in barley straw (Cocks and Thomson, 1988). The same
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relationships were found between rice straw height (Table 1) and leaf proportion (r 0:33) or stem proportion (r 0:38) in this study, but they were not signi®cant. A signi®cant correlation was found between leaf blade and sheath fractions (r 0:56, P < 0:05). The respective contribution of blades, sheaths and miscellaneous fractions to total leaves was variable among straw samples. A couple of straw samples (E and F) showed a low contribution of blades to total leaves which averaged 30.92% and three others (D, J and K) had the highest contribution averaging 53.3%. The presence of brittle parts (miscellaneous fraction) was low (mean 1.3%) in whole straw. It represented up to 5.2% of total leaves for straw E. When the miscellaneous fraction was high, the corresponding straw was more susceptible to brittleness than other. The miscellaneous proportion was negatively related (r 0:65, P < 0:01) to leaf blade fraction and not related (P 0:11) to leaf sheaths or total leaves. Therefore, the stem to leaf blade ratio should have a potential as an indicator of the susceptibility of straws to break easily, as well as grinding energy which is a measure of the resistance to particle size reduction. Negative relationships were found between grinding energy and intake (Pearce et al., 1998) in rice and wheat straws. A high stem to leaf blade ratio would therefore be related to low grinding energy of straw and to high intake. 3.3. Whole straw degradation after 24 and 72 h of rumen incubation Data for in sacco degradation of whole straws are given in Table 4. OM degradation values were close to that of DM. This low difference between both values could be due to a Table 4 In sacco degradation (%) of dry matter (DM) and organic matter (OM) of straw samples at 24 and 72 h of incubation Straw identification
DM
OM
24 h
72 h
24 h
72 h
A B C D E F G H I J K L M N O
31.4 29.0 31.0 32.3 26.8 26.6 29.9 30.7 29.4 28.0 36.3 35.3 30.8 30.1 28.8
51.4 48.9 50.4 52.7 43.7 43.6 49.7 51.1 51.1 50.0 56.4 57.6 48.7 50.4 48.7
30.9 24.4 28.2 30.5 25.0 23.6 28.4 31.3 29.2 25.4 35.6 35.6 29.4 29.0 28.3
51.7 47.0 49.4 52.8 42.7 42.2 49.4 52.3 51.6 49.0 57.0 58.7 48.0 51.3 49.3
Mean Minimum Maximum S.D.
30.4 26.6 36.3 2.7
50.3 43.6 57.6 3.7
29.0 23.6 35.6 3.6
50.2 42.2 58.7 4.4
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high ash loss from the bags during incubation. The variation between maximum and minimum values was 10% units for DM degraded at 24 h, to 17% units for OM degraded at 72 h. Differences between degradation values were more evident for OM than for DM, and for 72 than for 24 h. Degradation at 24 h for DM in rice straw samples was in the range of other reported values: 20.0 (Bae et al., 1997) to 40.8% (Adya et al., 1995). OM degradation at 24 h was lower than published data (Walli et al., 1988; Adya et al., 1995; Wilman et al., 1999), whereas for OM disappearance at 72 h, most of the rice straw samples (see Table 4) were in the range of reported values (49.3 to 61.5%) (Walli et al., 1988; Rahal et al., 1997). Whatever the time of incubation, the ranking of straw samples was equivalent either with DM or OM degradation. Ranking was different between 24 and 72 h, but differences were very small for intermediate samples. Moreover, the straw with the higher (straws K and L) and lower (straws E, F) DM or OM degradation were the same at both time of incubation. Since these straws samples were incubated in similar microbial environment, it can be suggested that the observed variations in straw degradation were related to their chemical and/or physical properties. 3.4. Relationship between degradation, and morphological and chemical composition of rice straw samples In the present work, all rice straw samples were grown under similar soil and identical agronomic conditions. Thus, the large variability in ruminal degradation between samples may be related to their genetic characteristics, re¯ected by a large variability in their morphological and chemical composition. We thus assessed the relationships between degradation, morphological and chemical composition of rice straw samples, by PCA. The ®rst two axes explained 64 to 69% of the variance for the 4 PCA. The ®rst axis discriminated the extent of degradation together with morphological and chemical parameters. Result for PCA 1 is given in Fig. 1. Concerning morphological variables, degradation was positively related to the proportion of total leaves (PCA 3 and 4), negatively related to the stem proportion and not related to chaff proportion. For leaves, degradation was positively related to leaf blade proportion and not related to leaf sheath (PCA 1 and 2). In agreement with these results, Flachowsky et al. (1991) reported that for 51 varieties of cereal straw (oat, barley, rye, wheat, triticale), the DM degradation after 48 h incubation in the rumen of sheep was negatively related to internode proportion and positively related to leaf proportion in whole straw. However, in previous works on degradation of morphological fractions of rice straw, it has been reported that degradability of stems was higher than or similar to that of leaf sheaths or blades, as observed in vitro (Bainton et al., 1986; Vadiveloo, 1995; Vadiveloo, 2000) and of leaves, as observed in sacco (Walli et al., 1988; Nakashima and érskov, 1990), whereas the adverse trend was observed for other Poaceae (Flachowsky et al., 1991). Our results suggest that the relationship between total leaves and degradation may largely depend on the blade proportion, which varies widely from 30 to 54% of total leaves in our study. This may explain the differences in the relationship between degradation and leaf proportion between experiments reported, as blade and sheath were not differentiated in some of them.
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Fig. 1. Representation on factorial circle of the first two axes, for principal component analysis 1 (PCA 1) of rice straw variability. 24: OM degraded at 24 h; 72: OM degraded at 72 h; circles: morphological factors; squares: chemical factors; LB: leaf blade; LS: leaf sheath; S: stem; Ch: chaff; Si: SiO2; CP: crude protein; H: hemicelluloses; Ce: cellulose; L: lignins.
Concerning chemical variables, degradation was positively related to hemicelluloses, whereas increasing NDF, cellulose and lignin tended to decrease degradation. The same trend was observed when ®bers (PCA 1 and 3) or ash-free ®bers (PCA 2 and 4) were taken into account. These ®ndings are in agreement with Tripathi et al. (1996) showing negative correlation between in sacco OM degradation and NDF (r 0:25), cellulose (r 0:10) and lignin (r 0:77). Also, Fall et al. (1998) reported that both NDF and ADF were negatively related to DM degradability of various varieties of cereal straw including rice. In our study, the linear relationships between cell wall components and whole straw OM degradation were stronger with ADF than with NDF (r 0:79 versus 0.58 at 24 h and 0.69 versus 0.43 at 72 h, for ADF versus NDF, respectively). This is in line with Fall et al. (1998) who reported that ADF was better than NDF for prediction of DM degradability of straw varieties. It should be emphasized that compared to NDF, ash-free NDF is poorly related to degradation (r 0:34 and 0.21 at 24 h and 72 h, respectively). Since the difference between NDF and ash-free NDF is attributed to ash from soil (Crocker et al., 1998), it may be suggested that ash from soil induced a depressive effect on degradation. This is not consistent with results given by direct measurements of ash and SiO2, which showed no negative relationship with degradation, whereas most previous studies focused on the effect of SiO2 on straw degradation reported a negative effect (Shimojo and Goto, 1989; Balasta et al., 1989; Fall et al., 1998). As discussed above, it may be due to the low content of SiO2 of straw samples in our study compared to samples from other geographic provenance (Doyle and Chanpongsang, 1990; Rahal et al., 1997; Abou-El-Enin et al., 1999). Since leaf blade proportion and hemicelluloses appeared to be the main morphological and chemical factors related to degradation, the linear relationships between leaf blade and/or
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Table 5 Linear relationships between OM degraded (%) and leaf blade proportion (%) and hemicellulose content (%) in rice straw samplesa Slopes
Intercept OM degraded 24 h
OM degraded 72 h
Leaf blade
17.58 (3.83)*** 17.79 (11.20) NSb 11.90 (12.08) NS ***
33.86 (4.16) 5.35 (14.66) NS 7.22 (14.19) NS
0.349 (0.115)** 0.149 (0.125) NS 0.498 (0.125)** 0.317 (0.147)
Hemicelluloses
r2
1.538 (0.368)** 1.185 (0.468)*
0.416 0.574 0.619
1.826 (0.482)** 1.071 (0.550)
0.550 0.525 0.658
a
Values in parentheses are standard error of estimates. Non-significant. P < 0:10. * P < 0:05. ** P < 0:01. *** P < 0:001. b
hemicelluloses and OM degradation were calculated (Table 5). The variability in degradation between straw samples at 24 h and 72 h was partly explained by leaf blade alone (42 and 55%, respectively) and hemicelluloses alone (57 and 53%, respectively). The model was improved when both morphological and chemical variables were included, allowing more than 60% of variability in degradation between straw samples to be explained (Fig. 2).
Fig. 2. Correlation between calculated and measured values for organic matter degradation after 24 (~) and 72 h ( ) incubation. Calculated values were obtained with the following equations: OM degraded at 24 h % 11:30 0:149 Leaf blade 1:185 Hemicelluloses; OM degraded at 72 h % 7:22 0:317 Leaf blade 1:071 Hemicelluloses. Closed line: X Y.
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4. Conclusion This study provides new information on the relationships between composition and ruminal degradation of rice straw varieties. Fractionation of whole straw samples showed that the variability in whole plant degradation was highly related to leaf blade proportions, which appeared to be better than total leaves as a criterion for ruminal degradability. Equations are proposed to assess the susceptibility of rice straw samples to ruminal degradation, according to chemical (hemicelluloses) and/or morphological (leaf blade) variables. No effect of SiO2 on straw degradation has been evidenced, but this may be related to the low SiO2 contents of straw samples, due to geographical and agronomic conditions. Acknowledgements The authors wish to thank D. Thomas for help in straw harvesting and C. Bardoux, M. Pezant and F. Duchier for fractionation of straw samples. They are grateful to M. Jamot for preparation of nylon bags and D. Roux for animal care and help in nylon bag management.
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