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Effects of increasing level of dietary rice straw on chewing activity, ruminal fermentation and fibrolytic enzyme activity in growing goats.


Rice is the most widely grown cereal crop and provides an important traditional feed source for ruminant animals in China. Increasing the level of rice straw in the diet leads to an increased dietary neutral detergent fibre (NDF) content. Studies have shown that increasing dietary rice straw negatively affects nutrient digestibility in ruminants (Fimbres et al., 2002; Zhao et al., 2007). However, increasing dietary NDF content may have a positive effect on the maintenance of normal rumen function, which is associated with adequate salivation, optimal pH for cellulolytic microorganisms and energy supply (Jaster and Murphy, 1983; Allen, 1997; Krause et al., 2002). Although some studies have been made in cattle and sheep, few have been done for goats.

Chewing activity, including eating and ruminating, has a direct relationship with the amount of saliva secretion, which is an important buffer for maintaining normal rumen functions (Allen, 1997). The rumen microorganisms, predominately bacteria, protozoa and phycomycete fungi, can secrete a wide range of fibrolytic enzymes (Imai, 1998; Chen et al., 2008). These enzymes, such as avicelase, CMCase, xylanase and cellobiase, account for the primary reactants on dietary carbohydrates and proteins (Santra et al., 2007). Higher dietary NDF content tends to increase salivation through eating and ruminating, and might benefit the growth of cellulolytic microbes (Lu et al., 2005). Therefore, it was important to examine the effect of increasing dietary rice straw and NDF level on fibrolytic enzyme activities, which have been rarely explored.

The effects of rice straw on site and extent of digestion and nitrogen (N) balance were reported in our previous study (Zhao et al., 2007). In the present study, the effect of increasing level of rice straw in the diet on chewing activities, ruminal fermentation and rumen fibrolytic enzyme activities were studied.


Animals and their management

A 4x4 Latin square experiment with 4 growing Liuyang black wether goats (a local breed, body weight of 19.3 [+ or -] 2.1 kg) was conducted. The goats were surgically fitted with ruminal fistulae. About 30 d were allowed for recovery of the animal from surgery. The experimental procedure was approved by the Animal Care Committee, ISA.

Rice straw and maize stover were used as the main sources of forage in this study. RS5, RS10, RS15 and RS20 were the diets which contained 0.05, 0.10, 0.15 and 0.20 rice straw. The diets were formulated to meet 1.3 times maintenance requirements of metabolisable energy according to our previous study (Zhao et al., 2007; Wang et al., 2008). Ingredients and composition of diets are shown in Table 1. The amount of diet offered to each goat was restricted to 850 g/kg of its ad libitum intake to ensure that there was no refusal during the whole experimental period. The forage was fed once daily at 07:30 h and the concentrate twice daily in two equal amounts at 08:00 and 20:00 h. All goats had free access to fresh water, and were kept individually in stainless steel metabolism cages (41 x 127 cm) in a temperature-controlled (at 20[degrees]C) house with constant lighting.

Each experimental period lasted for 26 d, comprised of 12 d adaptation and 14 d sampling with at least 3 d between periods. The amount of feed offered was weighed daily for each goat. Samples of the whole diet (about 0.1 kg) were collected daily and composited into one sample per goat during d 13 to 22, and dried at 65[degrees]C for 48 h for the determination of nutrient intake and digestibility. Feces were collected daily during the last 5 sampling days using faecal collection bags, and 10% representative samples were composited within goat and across days for each period (Zhao et al., 2009). Samples were stored at -20[degrees]C until analyses.


About 50 ml ruminal fluid was collected with a rumen filter probe tube via the ruminal cannula at 0.5, 3, 6, 9 and 12 h after the morning feeding on d 17 of each period. Samples were composited for analysis of fibrolytic enzyme activity. The fermentation was stopped by swirling the flasks in ice water. The volume of ruminal fluid was equally mixed with phosphate buffer solution (50 mM; pH = 6.0), and immediately squeezed through 4 layers of cheesecloth. The filtered fluid was centrifuged at 800xg for 15 min to obtain the supernatant fraction without small digesta particles, which was then treated by Ultrusonic Cell Disrupter and stored at -20[degrees]C for subsequent analysis of fibrolytic enzyme activities.

Ruminal pH and VFA were measured from d 18 to 19. Ruminal fluid samples (50 ml) were taken with a rumen filter probe tube via the ruminal cannula. Ruminal fluid samples (50 ml) were collected at 0.5, 2, 4, 6, 9, 12, 15, 18 and 21 h after the morning feeding on d 18 of each period. The pH was measured using a pH meter (REX, Shanghai instrument factory, pHS-3C). Ruminal samples were then immediately squeezed through 4 layers of cheesecloth. A 10 ml sample of filtered fluid was centrifuged at 20,000xg for 15 min at 4[degrees]C to obtain a clear supernatant which was then analyzed for ammonia using a phenol-hypochlorite assay (Zhao et al., 2009). For the determination of VFA, 10 ml of fluid was centrifuged at 500xg for 10 min at 4[degrees]C. The solution was then put into a plastic bottle containing 1 ml of 25% metaphosphoric acid and 1 ml of 0.6% 2-ethyl butyric acid (internal standard). The mixture was centrifuged at 20,000 xg for 15 min at 4[degrees]C and the supernatant was stored at -20[degrees]C for-analysis.

Chewing activity

Chewing activity was measured according to the procedure used in the previous study (Zhao et al., 2009). Eating and ruminating activities were monitored visually every 5 min for 24 h from d 22 to 23. Each activity was assumed to persist for the entire 5 min interval. Eating was defined as at least 1 min of eating activity after at least 20 min without eating. A period of rumination was defined as at least 5 min of rumination occurring after at least 5 min without ruminating. Time spent eating or ruminating per gram of dry matter intake (DMI) and neutral detergent fibre intake (NDFI) were calculated. Eating and rumination activities were expressed as total minutes for the 24 h period or on the basis of DMI and NDFI. Chewing activities were calculated as a sum of eating and ruminating activities.

Chemical analysis

Neutral detergent fibre (NDF) and acid detergent fibre (ADF) were determined using the methods of Van Soest et al. (1991). The NDF was assayed with the addition of a heat stable amylase, but without sodium sulphite. Dry matter (DM), organic matter (OM) and nitrogen (N) were determined according to AOAC (2002).

Ammonia was determined by a phenol-hypochlorite assay (Chaney and Marbach, 1962). The VFA was separated on a packed column (model SP-1200, Supelco, Bellefonte, PA) with 2-ethyl butyric acid as the internal standard, and quantified by gas chromatography (Hewlett Packard 5890, HP, USA).

Enzyme activities were determined by measuring reducing sugar formation from 0.5% sodium carboxymethylcellulose (i.e. 0.5 g sodium carboxymethylcellulose in 100 ml 0.2 M phosphate buffer solution) for carboxymethyl cellulase (CMCase) activity, from 0.5% avicel microcrystalline cellulose (i.e. 0.5 g avicel microcrystalline cellulose in 100 ml 0.2 M phosphate buffer solution) for avicelase, from 0.5% xylan (i.e. 0.5 g xylan in 100 ml 0.2 M phosphate buffer solution) for xylanase, and from 0.5% salicin (i.e. 0.5 g salicin in 100 ml 0.2 M phosphate buffer solution) for cellobiase, respectively. The enzyme reactions were initiated by addition of 0.2 ml enzyme solution and 1 ml substrate, and then incubated at 50[degrees]C for 90 min. After adding 2 ml of 3,5-dinitrosalicylic acid (DNS reagent), the reactions were stopped by heating in a boiling water bath for 10 min. The color formed was read at 550 nm with a Shimadzu UV-2450 Spectrophotometers (Japan). Glucose was used as standard for CMCase, avicelase and cellobiase, and xylose for xylanase, respectively. One international unit (IU) was equivalent to the enzyme activity releasing 1 [micro]mol of glucose or xylose per minute per ml of enzyme solution.

Statistical analysis

The data were analyzed as a 4x4 Latin square design using the GLM procedure of SAS software. The model used was: [Y.sub.ijkl] = [[mu].sub.i] + [G.sub.i] + [P.sub.j] + [T.sub.k] + [e.sub.ijkl] where [mu] is the overall mean, [G.sub.i] is the effect of goat (i = 1 to 4), [P.sub.j] is effect of period (j = 1 to 4), [T.sub.k] is fixed effect of treatment (k = 1 to 4), and [e.sub.ijkl] is residual. Where the treatment effect was significant, differences among means were tested with Duncan's multiple range tests. Statistical significances were considered to exist if p<0.05. Orthogonal polynomial contrasts were used to examine the responses (linear and quadratic) to increased level of rice straw in the diets.


Chewing activity

Effects of increasing level of dietary rice straw on chewing activity in goats are shown in Table 2. Dietary rice straw level increased the time spent in eating, ruminating and chewing activities ([P.sub.linear effect] <0.01). Increasing level of rice straw increased min/g DM ([P.sub.linear effect] <0.01) and min/g NDFI ([P.sub.linear effect] <0.05) for eating activities, min/g DM ([P.sub.linear effect] = 0.01) for ruminating activity, and min/g DM ([P.sub.linear effect] <0.01) and min/g NDFI ([P.sub.linear effect] <0.01) for chewing activities.

Ruminal fermentation

Effect of increasing level of rice straw on ruminal fermentation is shown in Table 3. Increasing dietary rice straw increased pH ([P.sub.linear effect] <0.05), acetate: propionate ratio ([P.sub.linear effect] <0.01), and decreased NH3-N concentration (Plinear effect<0.01) in the rumen. Dietary rice straw greatly affected ([P.sub.quadratic effect] <0.01) the total VFA concentration in rumen, with the lowest value observed in the RS10 group. Further investigating the individual VFA, increasing level of dietary rice straw also increased acetate ([P.sub.linear effect] <0.01) and isovalerate ([P.sub.linear effect] = 0.01), and decreased propionate ([P.sub.linear effect] <0.01) in the rumen.

Fibrolytic enzyme activity

Increased level of dietary rice straw decreased CMCase ([P.sub.linear effect] = 0.02), xylanase ([P.sub.linear effect] <0.01) and cellobiase ([P.sub.linear effect] <0.01) activities, but increased the avicelase ([P.sub.linear effect] <0.01) activity (Table 4).


The goats spent 227-362, 223-333, and 450-695 min/d for eating, ruminating and chewing activities, and an elevated level of rice straw increased the time spent on these three activities. The results were consistent with reports on other small ruminants (Kawas et al., 1991; Fimbres et al., 2002), although the extent of increased chewing activity might be different. Research on lambs showed that eating, ruminating and chewing time ranged from 92 to 75, 143 to 413 and 235-558 min/d, respectively, when grass hay increased from 0 to 30% in the diet (Fimbres et al., 2002). Research on sheep showed that eating, ruminating and chewing time ranged from 324 to 372, 486 to 558 and 810-930 min/d, respectively, when high forage rations were fed (from 40 to 80% grass hay) (Kawas et al., 1991). Increasing forage level caused an increased dietary fibre in the diet, which showed a great impact on chewing activity (Armentano and Pereira, 1997; Yang et al., 2001). However, the extent of response of chewing activity to the dietary fibre might be different. Beauchemin (1991) reported that the total chewing time increased by 11% as NDF content of the diet increased from 31 to 37% in dairy cows. Oba and Allen (2000) observed that the total chewing time increased by 21% as NDF content of the diet increased from 29 to 38% in dairy cows. In our study, total chewing time by goats was more sensitive to changes in NDF content than in larger animals, and increased by 56% as NDF content increased from 31.5 to 39.7%.

Increasing level of dietary rice straw linearly increased the ruminal pH and acetate: propionate ratio, and decreased NH3-N concentration. Increased acetate:propionate ratio in the rumen indicated a reduced energy efficiency. The results are in agreement with the generally accepted perception that dietary NDF maintains normal rumen function, which is associated with adequate salivation, optimal pH for cellulolytic microorganisms and energy supply (Beauchemin, 1991; Oba and Allen, 2000). Further investigating the molar proportion of individual VFA in the rumen, the increased acetate and iso-valerate and decreased propionate were consistent with many previous studies (Zinn et al., 1994; Lu et al., 2005). Lu et al. (2005) reported that a concentrate diet yielded a higher proportion of propionate, and a forage diet yielded more acetic, butyrate and iso-butyrate. Zinn et al. (1994) reported that increasing the forage level from 10 to 20% increased ruminal molar proportion of acetate, but did not affect molar proportions of butyrate. It was likely that the increased dietary rice straw elevated ruminal pH, and thus favored the growth of cellulolytic microbes (e.g. Fibrobacter succinogenes and Ruminococcus flavefaciens) and thereby increased acetate production (Lu et al., 2005; Zebeli et al., 2008).

Increased level of dietary rice straw decreased N[H.sub.3]-N concentration in the rumen. Decreased ruminal N[H.sub.3]-N concentration might lead to a decreased efficiency of N use in ruminant animals, and was consistent with previous research on N balance, which showed that rice straw decreased N cycling back to the digestive tract in goats, as increased faecal and urea N, and decreased apparently absorbed and retained N (Zhao et al., 2007). Although increased avicelase enzyme was observed, the other three fibrolytic enzymes, CMCase, xylanase and cellobiase, were decreased. So, increasing the level of rice straw leaded to the low efficiency of use of nutritive substrates in the diet. The results were in agreement with our previous study, which showed that increased dietary rice straw decreased the potential digestibility of DM and fibre in goats (Zhao et al., 2007). Increased dietary fibre might be of benefit in maintaining rumen health, but sacrifices efficiency of nutritional use of the diet (Zhao et al., 2007).


Increasing level of dietary rice straw from 5-20% leaded to an increase of NDF content from 31.5 to 39.7% in the diet, which increased chewing activity and ruminal pH, and affected ruminal fermentation metabolites in goats. Increased acetate:propionate ratio in the rumen indicated reduced energy efficiency when dietary rice straw content was increased. In addition, analysis of fibrolytic enzymes indicated that increasing level of dietary rice straw decreased the ruminal CMCase, xylanase and cellobiase activities, and increased ruminal avicelase activity.


The authors would like to thank the Knowledge

Innovation Program of CAS (Grant No. KZCX2-XB2-08, Grant No. 0823055111), and Realm Frontier Project of ISA (Grant No. 0751012010) for the joint financial support.


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M. Wang (a), X. G Zhao (a), Z. L. Tan *, S. X. Tang, C. S. Zhou, Z. H. Sun, X. F. Han and C. W. Wang (1)

Key Laboratory of Agro-ecological Processes of Subtropical Region Huanjiang Observation and Research Station of Karst Agro-ecosystem, Institute of Subtropical Agriculture the Chinese Academy of Sciences, Changsha P.O. Box 10, Hunan 410125, China

* Corresponding Author: Z. L. Tan. Tel: +86-7314619702, Fax: +86-7314612685, E-mail:

(1) College of Animal Science and Technology, Jiangxi Agriculture University, Jiangxi Institute of Veterinary Drug and Feedstuff Control, Nanchang, 330045, China.

(2) The authors contributed equally to this work as co-first author.

Received August 3, 2009; Accepted January 11, 2010
Table 1. Dietary ingredients and chemical composition (1)


Item                          RS5      RS10      RS15      RS20

Ingredient (%)
  Maize stover               20.0      20.0      20.0      20.0
  Rice straw                  5.00     10.0      15.0      20.0
  Ground corn                41.0      35.4      29.7      24.0
  Soybean meal                7.30      8.00      8.60      9.30
  Wheat bran                 19.2      19.2      19.2      19.2
  Corn starch                 0.10      0.10      0.10      0.10
  Fish meal                   4.60      4.60      4.60      4.60
  Urea                        0.17      0.17      0.17      0.17
  Sodium chloride             0.50      0.50      0.50      0.50
  Calcium carbonate           0.58      0.58      0.58      0.58
  Premix (2)                  1.50      1.50      1.50      1.50

Chemical composition (3)
  DM (%)                     85.7      86        86.2      86.4
  OM (%)                     92.5      92.6      91.6      93.1
  CP (%)                     14.9      14.9      14.9      14.9
  NDF (%)                    31.5      34.2      36.7      39.7
  NDF from forage (%)        16.6      19.9      23.2      26.6
  ADF (%)                    17.3      19.4      21.5      23.6
  Ca (%)                      0.63      0.64      0.65      0.67
  P (%)                       0.39      0.39      0.39      0.39
  ME (4) (Mcal/kg DM)         2.44      2.37      2.29      2.21

(1) Values expressed on a dry matter basis.

(2) Premix contained per kilogram: 119 g MgS[O.sub.4] x [H.sub.2]O,
2.5 g FeS[O.sub.4] x 7[H.sub.2]O, 0.8 g CuS[O.sub.4]-5[H.sub.2]O,
3 g MnS[O.sub.4]-[H.sub.2]O, 5 g ZnS[O.sub.4] x [H.sub.2]O, 10 mg
[Na.sub.2]Se[O.sub.3], 40 mg KI, 30 mg Co[Cl.sub.2]-6[H.sub.2]O,
95,000 IU vitamin A, 17,500 IU vitamin D, and 18,000 IU vitamin E.

(3) The chemical composition was analyzed except for metabolizable
energy (ME) which was calculated from the data of Zhang and Zhang
(1998); DM = Dry matter, OM = Organic matter, CP = Crude protein, NDF
= Neutral detergent fibre, ADF = Acid detergent fibre, P = Phosphorus.

Table 2. Effect of increasing level of rice straw on the eating,
rumination and chewing activities of goats (n = 4) (1)

                                       Diets (2)

Item                RS5          RS10          RS15          RS20

  Min/d          227 b         250 b         300 b         362 a
  Min/g DMI        0.45 b        0.50 b        0.59 b        0.71 a
  Min/g NDFI       1.43 b        1.44 b        1.60 ab       1.81 a

  Min/d          223 b         259 ab        306 ab        333 a
  Min/g DMI        0.44 b        0.51 ab       0.60 a        0.66 a
  Min/g NDFI       1.40          1.49          1.63          1.66

  Min/d          450 c         509 c         606 b         695 a
  Min/g DMI        0.89 c        1.00 c        1.20 b        1.37 a
  Min/g NDFI       2.82 c        2.94 bc       3.24 ab       3.46 a


Item                SEM        Linear        Quadratic

  Min/d            16.9        <0.01           0.29
  Min/g DMI         0.03       <0.01           0.31
  Min/g NDFI        0.09        0.02           0.35

  Min/d            21.8        <0.01           0.84
  Min/g DMI         0.04        0.01           0.80
  Min/g NDFI        0.13        0.16           0.80

  Min/d            20.1        <0.01           0.48
  Min/g DMI         0.23       <0.01           0.46
  Min/g NDFI        0.11       <0.01           0.64

(1) DMI, NDFI and SEM were dry matter per day, neutral detergent fibre
intake per day and pooled standard error of means, respectively. Means
with different letters within a row are significantly different
(p < 0.05).

(2) RS5, RS10, RS15 and RS20 contained 0.05, 0.10, 0.15 and 0.20 rice
straw, respectively.

Table 3. Effect of increasing level of rice straw on ruminal pH
and fermentation metabolites of goats (1)

                                              Diets (2)

Item                               RS5          RS10          RS15

pH                                6.21 b        6.27 ab       6.32 ab
N[H.sub.3]-N (mg/100 ml)         25.3 a        24.0 b        23.1 bc
Total VFA (mmol)                112 a         100 b         113 a
Acetate:propionate                1.46 b        1.44 b        1.65 b
Individual VFA (% of total)
  Acetate                        47.0 b        47.0 b        48.7 b
  Propionate                     32.5 a        34.3 a        29.9 a
  Butyrate                       15.2          13.9          16.2
  Iso-butyrate                    1.6           1.66          1.67
  Iso-valerate                    2.00 b        1.80 c        2.02 b
  Valerate                        1.64          1.34          1.50

                                        Diets (2)

Item                              RS20           SEM

pH                                6.39 a        0.04
N[H.sub.3]-N (mg/100 ml)         22.4 c         0.37
Total VFA (mmol)                113 a           1.46
Acetate:propionate                2.12 a        0.07
Individual VFA (% of total)
  Acetate                        53.0 a         0.88
  Propionate                     26.4 b         0.95
  Butyrate                       14.8           0.97
  Iso-butyrate                    1.84          0.07
  Iso-valerate                    2.39 a        0.10
  Valerate                        1.53          0.09


Item                             Linear       Quadratic

pH                                 0.01         0.95
N[H.sub.3]-N (mg/100 ml)          <0.01         0.43
Total VFA (mmol)                   0.06         0.01
Acetate:propionate                <0.01         0.02
Individual VFA (% of total)
  Acetate                         <0.01         0.09
  Propionate                      <0.01         0.02
  Butyrate                         0.04         0.40
  Iso-butyrate                     0.80         0.99
  Iso-valerate                     0.01         0.01
  Valerate                         0.59         0.06

(1) Means with different letters within a row are significantly
different (p < 0.05), SEM is pooled standard error of means.

(2) RS5, RS10, RS15 and RS20 contained 0.05, 0.10, 0.15 and 0.20 rice
straw, respectively.

Table 4. Effect of increasing level of rice straw on activity of
avicelase, CMCase, xylanase and cellobiase (n = 4) (1)

                                     Diets (2)

Item              RS5          RS10          RS15          RS20

Avicelase        5.59 b        6.38 a        6.09 a        6.33 a
CMCase           3.96 a        3.13 b        3.77 a        3.30 b
Xylanase        14.7 a        13.8 b        12.4 c        13.4 b
Cellobiase       3.83 a        3.07 b        3.09 b        3.12 b

Item              SEM         Linear       Quadratic

Avicelase        0.18           0.02          0.09
CMCase           0.11          <0.01          0.03
Xylanase         0.21          <0.01         <0.01
Cellobiase       0.08          <0.01         <0.01

(1) Means with different letters within a row are significantly
different (p < 0.05); SEM is pooled standard error of means.

(2) RS5, RS10, RS15 and RS20 contained 0.05, 0.10, 0.15 and
0.20 rice straw, respectively.
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Author:Wang, M.; Zhao, X.G.; Tan, Z.L.; Tang, S.X.; Zhou, C.S.; Sun, Z.H.; Han, X.F.; Wang, C.W.
Publication:Asian - Australasian Journal of Animal Sciences
Geographic Code:9CHIN
Date:Jul 15, 2010
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