Livestock Research for Rural Development 13 (4) 2001

Citation of this paper

Effects of treatment of rice straw with lime and/or urea on its intake, digestibility and rumen liquor characteristics in cattle

Nguyen Xuan Trach, Magne Mo*, Cu Xuan Dan 

Faculty of Animal Science and Veterinary Medicine, Hanoi Agricultural University
* Department of Animal Science, Agricultural University of Norway

 

Abstract

Two trials were carried out to compare voluntary intake and digestibility of rice straw which was treated according to a 3 x 3 factorial design using unslaked lime (0, 3, and 6%, w/w) and urea (0, 2, and 4%, w/w). In Trial 1, 27 growing beef bulls were divided into 9 groups to be fed on the 9 types of straw. Voluntary intake was first measured, followed by digestibility determination when a restricted level of straw (47 g OM/kg W0.75/day) was fed. In Trial 2, three rumen-fistulated adult oxen were fed ad libitum (20% in excess) on the same 9 types of straw to determine intake and digestibility concurrently. 

It was found that both lime and urea significantly increased straw intake, digestibility, and thus its energy availability. The intake and digestibility of 2% urea-treated straws and especially 4% urea-treated straws were higher than those of untreated straw. A level of 3% lime significantly increased straw intake and digestibility. Treatment with 6% lime continued to increase apparent digestibility, but depressed straw intake compared with 3% lime in Trial 1. In addition, rumen liquor analyses showed that rumen ammonia (NH3) and total volatile fatty acids (VFA) were decreased by the treatments. 

The findings suggest that both lime and urea are effective in increasing straw intake and apparent digestibility.

Keywords: Rice straw, urea, lime, cattle, intake, digestibility

 

Introduction

Treatments of rice straw with lime and/or urea were effective as judged by chemical composition, in-vitro gas production and in-sacco degradability (Nguyen Xuan Trach et al 2001). However, a measure to improve the feeding value of straw, as a roughage, must then result in increased voluntary intake, digestibility and consequently available energy. This is because animal performance is the product of supply, nutrient concentration, intake, digestibility, and metabolism (Mertens 1994). Voluntary intake and digestibility are thus of great importance in evaluating roughage quality. Direct measurements or estimates of them have always been of major interest to nutritionists (Burns et al 1994; Cochran and Galyean 1994; Weiss 1994; Ørskov 1998). Measurements of these properties would provide convincing indicators for evaluation of different treatments to improve rice straw quality. 

The present paper reports two intake-digestion trials, one on growing and the other on adult cattle, to further evaluate straw treatments using lime and/or urea. In addition, rumen liquor parameters were measured to provide additional insights into the mechanisms of the treatment effects.


Materials and methods

Straw treatment

Sun-dried rice straw (90% DM) in the long form was treated with quick lime (87% CaO) at  0%, 3% or 6% (w/w) in combination with urea (46% N) at 0%, 2% or 4% (w/w) according to a 3 x 3 factorial design. The treatment chemicals were dissolved in required amounts of water to attain 50% moisture content for the treated straw. The respective solution/suspension was then sprayed onto the straw with a watering can and thoroughly mixed manually. The mixed straw was then placed in polyethylene sacks (90 cm x 120cm), which each had been put inside another woven plastic sack of the same size, and sealed after being carefully pressed to remove as much air as possible. The sacks were then stored in a shed for 3 weeks at an average ambient temperature of around 25oC.

Animals and feeding regimes

In Trial 1, a total of 27 growing bulls of a tropical beef breed (Bos indicus) at 12-15 months of age with an average live-weight of 116kg were allocated into the 9 groups to be fed on the straws. All animals were dewormed prior to commencement of the experiment. The animals underwent a transition period of 3 weeks to stabilize straw intake and after that voluntary intake measurements were made for 10 days. For the following 10 days all the animals were fed straw at a restricted level of 47g OM/kg/W0.75/day (equal to 80% of the determined voluntary intake of untreated straw) in preparation for a total collection period of 11 days, during which time the animals remained on restricted intakes. In Trial 2, three fistulated adult yellow oxen of the same breed (251, 269 and 236kg) were fed ad libitum (20% in excess) in turn on the same 9 types of straw in a random order. For each type of straw, voluntary intake measurement, faeces collection and rumen liquor sampling were concurrently made within 11 days following a 15-day adaptation period.

In both trials, animals were kept in a well-ventilated shed with a cement floor and fed in individual pens. Rice straw was the sole energy source in the diets, which were supplemented with 1% of bone meal and 1% of a vitamin-mineral mixture. Urea, 32 g and 16 g/kg straw respectively, was additionally given to the 0% and 2% urea-treated straws prior to feeding to equalize the total N level to that of 4% urea-treated straw (20 % urea-N already lost after treatment) in order to exclude the effect of nitrogen supplementation. The added urea was dissolved in required amounts of water before spraying to maintain the moisture of untreated straw similar to that of the treated straws (approximate 50%). Drinking water was freely supplied at all times.

Straw voluntary intake measurement

Voluntary intake of straw was measured according to Burns et al (1994). Straw was given twice a day at 7 am and 4 pm with 20% in excess of the average intake of the previous 5 days. All the residues left from the previous day were removed from the feeding trough in the morning and weighed. A sample of 100 g was then taken to create a pooled sample for the whole collection period. Newly fed straw was also sampled from the trough with 100 g taken every day to create a composite sample for each type of straw. Animal weights were recorded at the beginning and end of the intake and/or digestion periods. Straw dry matter (DM) and organic matter (OM) intakes were expressed both as a percentage of live-weight (% LW) and in g per kg metabolic weight (g kg/W0.75).

Digestibility determination and energy estimation

Digestibility determination was organized according to Cochran and Galyean (1994).  Representative samples of the straws were taken at feeding and saved as part of the "running" composite samples for 10 days. Faeces collection began 1 day following the start of straw sampling.  It was quantitatively collected immediately after excretion and 5% of the bulked faeces were then taken to make a composite sample for 10 days for each type of straw per animal. The running samples of straw and faeces were then stored at -20oC for subsequent analyses. Before chemical analysis the representative samples of straws and faeces were thawed and mixed thoroughly. A portion of each composite sample was taken and pre-dried at 55oC for 72h in a forced air draught oven, then left to cool for 4 h and ground to pass a 1mm screen.

The apparent digestibility was calculated according to Cochran and Galyean (1994) for organic matter (OMD) and neutral detergent fibre (NDFD). The formulae proposed by van Es (1978) for estimation of metabolisable energy of a low protein roughage was used to estimate rice straw energy availability, which is ME (MJ) = 15.1 * DOM, where ME is metabolisable energy in Mega-joule (MJ) and DOM is digestible organic matter. Metabolisable energy of straw in the present case was calculated particularly on an organic matter (OM) basis to exclude the differences in the ash content of straw DM due to lime treatment.

Rumen liquor sampling

Rumen liquor samples were collected on two consecutive days in the middle of each collection period in Trial 2 between three and four hours after the morning feeding. Samples were taken with a 50 ml syringe connected to a 50 cm long plastic tube introduced through the fistula. The pH value of rumen liquor was determined immediately after the sample was taken using a portable pH meter. Each sample of 25 ml was then placed in a 30ml bottle acidified with 5 drops of concentrated sulphuric acid and then stored at -20oC until analysed for ammonia (NH3) and total volatile fatty acids (VFA).

Chemical analysis

Straw and faeces samples were analysed for dry matter (DM) and crude ash according to AOAC (Cunniff 1997). NDF content was determined according to Van Soest and Robertson (1985). Ammonia was separated from rumen liquor by steam distillation, collected in boric acid solution and determined by titration with standard acid (Preston 1995). Total VFA was also determined by steam distillation according to AOAC (Cunniff 1997).

Statistical analysis

Data were analysed using the GLM (General Linear Model) procedure of the SAS package (1996). For trial 1, a fixed 3x3 factorial model of analysis of variance (ANOVA) was applied. Factor level means were separated by the Ryan-Einot-Gabriel-Welsch (REGWQ) multiple range test. In addition, the two levels of urea (2% and 4%) as well as the two levels of lime (3% and 6%) were linearly combined together to contrast with non-urea or non- lime treated straw, respectively. For Trial 2, similar procedures were applied, except that the animal factor was included in the model as a block.


Results

Voluntary intake of straw

Both lime and urea increased straw OMI in both trials (Table 1). The intake of 6% lime-treated straw tended to be lower than that of 3% treated straw in growing cattle and almost the same between the two lime levels in adult cattle. Growing cattle tended to respond better to straw treatment in terms of intake. For example, treatment with 2% urea plus 3% lime increased OMI  by 32% in growing cattle compared to 24% in adult cattle. No significant interaction between lime and urea was found in adult cattle, but it was significant in the growing cattle of Trial 1. When urea was combined with lime, the differences in OMI between the two levels of urea (2% and 4%) were no longer apparent.    

 

Table1: Effects of treatment with lime and/or urea on organic matter intake (OMI) of rice straw by growing and adult cattle

Treatment

Chemical input (%)

Growing cattle (Trial 1)

Adult cattle (Trial 2)

Lime

Urea

% LW

g kg/W0.75

% LW

g kg/W0.75

                         Means by treatment

I

0

0

1.79a

58.7a

1.80a

71.6a

II

0

2

2.15b

70.4bc

1.96b

78.2b

II

0

4

2.34bc

77.1c

2.14c

85.0c

IV

3

0

2.29bc

77.3c

 2.09bc

 83.3bc

V

3

2

2.40c

77.5c

2.24c

88.8c

VI

3

4

2.39c

78.9c

2.24c

89.0c

VII

6

0

2.13b

69.4b

2.13c

84.6c

VIII

6

2

2.32bc

75.7c

2.24c

89.0c

IX

6

4

2.25bc

74.3bc

2.25c

89.1c

SEM

 0.07

2.0

              0.05

      2.0

                                                                           Factorial effects and contrasts

Lime

**

***

***

***

Urea

***

***

***

***

Urea x Lime

*

**

Ns

Ns

Animal

-

-

Ns

Ns

Lime vs. No lime

***

***

***

***

Urea vs. No urea

***

***

***

***

* P<0.05, ** P<0.01, *** P<0.001, Ns: non-significant;
Means within each column under the same subheading bearing the same superscript (a, b, c, d) are not significantly different at P<0.05.

Apparent digestibility and energy availability

It was found in Trial 1 that both lime and urea increased OMD and NDFD (Table 2). When urea was used in combination with lime no significant difference was found between the two levels of urea. The differences between 3% and 6% lime were not statistically significant. In Trial 2 (ad libitum feeding) the OMD and NDFD appeared to be lower than in Trial 1 (restricted feeding) (Table 3). For instance, 3% lime plus 2% urea increased OMD by 13.0 percentage points in Trial 1, compared to only 10.5 percentage points in Trial 2. Treatment effects in Trial 2 were not as clear as in Trial 1. In both trials OMD was significantly (P<0.001) increased by both lime and urea without any significant interaction found between the two chemicals. NDFD was also increased  (P<0.001) by both lime and urea with a significant interaction (P<0.05) to reduce their additive effects in Trial 1. In Trial 2 the effect of lime on NDFD was still significant (P<0.01), whereas urea apparently increased NDFD in absolute terms but the effect was not statistically significant (P = 0.08).

Table 2: Apparent digestibility and estimated metabolisable energy (ME) of rice straw treated with lime and/or urea and fed to growing cattle at a restricted level (Trial 1)

Treatment

Chemical input (%)

Apparent digestibility (%)

ME

Lime

Urea

OMD

NDFD

(MJ kg/OM)

Means by treatment

I

0

0

49.3a

53.6a

7.45a

II

0

2

55.9b

58.4b

8.44b

II

0

4

59.5c

63.5cd

8.98b

IV

3

0

57.8b

61.4c

8.73b

V

3

2

62.3c

65.6d

9.41c

VI

3

4

63.2c

65.4d

9.54c

VII

6

0

58.1b

62.1c

8.77b

VIII

6

2

62.6c

66.0d

9.45c

IX

6

4

64.3c

66.2d

9.70c

SEM

             0.9

              0.9

            0.14

                                                                        Factorial effects and contrasts

Lime

***

***

***

Urea

***

***

***

Urea x lime

Ns

*

Ns

Lime vs. No lime

***

***

***

Urea vs. No urea

***

***

***

Notes:  OMD = organic matter digestibility, NDFD = neutral detergent fibre digestibility, SEM  = standard error of mean; * P<0.05, ** P<0.01, *** P<0.001, Ns: non-significant; Means within each column under the same subheading bearing the same superscript (abcd) are not different at P<0.05.


Table 3:
Apparent digestibility coefficients and estimated metabolisable energy (ME) of rice straw treated with lime and/or urea fed ad libitum to adult cattle (Trial 2)

Treatment

Chemical  input (%)

Apparent digestibility (%)

ME

Lime

Urea

OMD

NDFD

(MJ kg/OM)

                                                                                 Means by treatment

I

0

0

48.2a

50.3a

7.27a

II

0

2

53.9b

54.3a

8.13b

II

0

4

57.1c

59.8b

8.63c

IV

3

0

55.5bc

58.3ab

8.37bc

V

3

2

58.7cd

60.5b

8.87cd

VI

3

4

60.3d

61.0b

9.10d

VII

6

0

56.6bc

59.7b

8.55bc

VIII

6

2

60.5d

61.3b

9.14d

IX

6

4

60.2cd

60.8b

9.10d

SEM

  1.0

  1.5

0.15

                                                                        Factorial effects and contrasts

Lime

***

**

***

Urea

***

0.08

***

Urea x lime

Ns

Ns

Ns

Animal

*

Ns

*

Lime vs. No lime

***

**

***

Urea vs. No urea

***

0.06

***

Notes:  OMD = organic matter digestibility, NDFD = neutral detergent fibre digestibility, SEM  = standard error of mean; * P<0.05, ** P<0.01, *** P<0.001, Ns: non-significant; Means within each column under the same subheading bearing the same superscript (abcd) are not significantly different at P<0.05.

Straw ME was greatly increased by lime and/or urea treatment (P<0.001). As a result of higher digestibility due to restricted feeding, the straw ME values were higher in Trial 1 than in Trial 2. Compared to untreated straw, the value of ME was increased by 32% and 26% due to the best treatment in Trial 1 and Trial 2, respectively. In the absolute terms, combination of 6% lime with 4% urea (in Trial 1) or 2% urea (Trial 2) resulted in the highest values of straw ME. However, when lime and urea were combined for treatment, the differences in effect on straw ME between 4% and 2% urea or 6% and 3% lime were not significant.

Rumen liquor parameters

Rumen pH and NH3 tended to decline while VFA increased with increasing application rates of urea for treatment, although the effects of lime and urea on rumen pH were non-significant (Table 4). Rumen NH3 concentration was lowest for diets based on 4% urea-treated straw and highest for urea-supplemented untreated straw diets. The contrast setting revealed a significant influence of lime treatment on rumen NH3 concentration (P<0.05). Both lime and urea significantly increased rumen VFA. However, no significant differences between the effects of 3% and 6% lime on the three parameters of rumen liquor were detected.

Table 4: Rumen liquor pH, ammonia (NH3) and total volatile fatty acids (VFA) contents in cattle fed on rice straw treated with lime and/or urea

Treatment

Chemical input (%)

Rumen liquor parameters

Lime

Urea

pH

NH3 (mg/litre)

VFA (mmol/litre)

                                                                                 Means by treatment

I

0

0

7.03

297a

70.6a

II

0

2

6.87

280ab

82.1b

II

0

4

6.84

258b

93.3c

IV

3

0

6.95

286a

84.6b

V

3

2

6.82

262b

93.2c

VI

3

4

6.78

247b

97.3c

VII

6

0

6.85

277ab

86.0bc

VIII

6

2

6.86

263b

93.3c

IX

6

4

6.81

255b

95.3c

SEM

                 0.05

             9

              2.9

                                                                        Factorial effects and contrasts

Lime

Ns

Ns

***

Urea

Ns

***

***

Urea x lime

Ns

Ns

Ns

Animal

Ns

Ns

*

Lime vs. No lime

Ns

*

***

Urea vs. No urea

Ns

***

***

Notes:  * P<0.05, ** P<0.01, *** P<0.001, Ns:  non-significant; Means within each column under the same subheading bearing the same superscript (abc) are not significantly different at P<0.05.

Discussion

Effect of treatment on straw voluntary intake

Urea treatment may increase intake of straw in the range of 15 to 50% as reviewed by Chenost and Kayouli (1997). Straw intake was increased by urea treatment in the present study in the lower half of this range. This is probably because in the present study, untreated straw was supplemented with urea at feeding. In non-supplemented rice straw the crude protein content is too low to meet the requirement of rumen microbes and thus supplementation of NPN increases digestion and thus intake due to increased microbial protein production (Doyle et al 1986; Djajanegara and Doyle 1989). Therefore, it has usually been uncertain to what extent the increased nutritive value of urea-treated straw is a result of NPN supplementation and to what extent it is a result of changes in the structure of the straw due to treatment effects (Schiere and Nell 1993). However, the increases in straw intake found in the present study were probably due only to treatment effect because N was no longer a limiting factor in all the straws under comparison owing to urea supplementation prior to feeding.

The increased straw intake due to present treatments may thus be explained by virtue of its increased degradability in the rumen as previously reported (Nguyen Xuan Trach et al 2001). An increase in the outflow of straw cell walls into the abomasum as a result of alkali treatment has also been reported (Males 1987). These possible effects of alkali treatment can aid in explaining the increases in straw intake in the present study.

Effect of treatment on apparent digestibility

The present findings show that both lime and urea are effective in increasing OMD and NDFD. In general, the higher the level of lime and/or urea applied in the present study, the more digestible the treated straw became. This was in agreement with the increased delignification, in-vitro gas production and in-sacco degradability of straw due to the treatments (Nguyen Xuan Trach et al 2001). Increased straw digestibility due to urea treatment has been well documented previously (Sundstøl and Coxworth 1984; Doyle et al 1986; Schiere and Ibrahim 1989; Chenost and Kayouli 1997; Madrid et al 1997). That lime treatment in the present study increased apparent digestibility of rice straw is in agreement with Selvendran et al (1977), Saadullah et al (1981) and Chaudhry (1998). Improvements in straw apparent digestibility as a result of treatment with lime and urea in combination have also been reported by Zaman and Owen (1990) and Sahoo et al (2000). 

Since the rumen is the primary site for fibre digestion, the increases in apparent digestibility of the treated straws were presumably due to increased rumen degradability resulted from increased susceptibility of structural carbohydrates of straw cell walls to rumen fermentation as well as more energy being made available for better growth of rumen microbes which degrade straw (Silva and Ørskov 1988; Rai and Mudgal 1988). The rumen retention time is actually not sufficient for the maximal fermentation of the substrate, thus an increase in degradation rate, as a result of increased straw degradability and better microbial activity, would cause a substantial improvement in digestibility and also in voluntary intake (Ørskov 1994).

In the present study, NDFD was slightly higher than OMD. This may be because measurements of apparent NDF digestibility over-estimated the digestibility of original cell wall material for treated straws since the compounds, which are solubilised, are unlikely to be completely digested (Djajanegara and Doyle 1989). Moreover, the determination of NDF is not confounded with any endogenous or microbial sources in the faeces.

Although not compared statistically, the apparent digestibility of straw cell wall components was generally higher in Trial 1 than in Trial 2. This is in agreement with the finding by Misra et al (1995) that digestibility of NDF was higher under restricted feeding of wheat straw and rice straw compared with ad libitum feeding regimes. This may be related to longer retention time under restricted feeding since the extent of degradation can be increased if rumen retention time is prolonged (Ørskov 1994).

Effect of treatment on rumen liquor parameters

The general decreases in rumen liquor pH and increases in VFA (Table 4) due to the treatments were probably a reflection of the improvements in the ruminal fermentation rate as previously found (Nguyen Xuan Trach et al 2001), which resulted in increased OMD and NDFD (Tables 2 and 3). Those groups with higher digestibilities showed higher values of VFA and lower values of pH. This is presumably because VFA was the end product of rumen microbial degradation of straw, and the more the VFA produced, the lower the resulting rumen pH. Jayasuriya et al (1987) have concluded that the output of VFA increases with the increase in feed intake. This explains the increased VFA content in the present observation.

Although the N level in straw was deliberately equalized prior to feeding, urea-treated straws resulted in lower rumen NH3 concentrations than urea-supplemented straws. Singh and Gupta (1988) have also found significant lower ammonia nitrogen concentration in strained rumen liquor in buffaloes fed on ammonia treated straw compared with untreated straw. The higher rumen NH3 resulted from supplemented straws may have been due also to greater part of the urea from the supplemented diets converted to free ammonia than the N provided by the urea-treated straws  (Chermiti et al 1994). More favourable conditions for rumen microbes to grow and thus capture more free ammonia in the rumen liquor (Singh and Gupta 1988; Chaudhry 1998) may be another explanation for the reduced rumen ammonia concentration due to lime and/or urea treatment.

Level of lime application for straw treatment

Results of our previous study (Nguyen Xuan Trach et al 2001) indicated that the effect of lime on in-sacco degradability and in-vitro fermentability of rice straw was increased with increasing application level. However, the present in-vivo results showed that 6% lime was not significantly better than 3% lime in increasing straw intake, digestibility and VFA. A level of 6% lime even reduced straw intake in growing cattle, compared with 3% lime. This would suggest some negative responses in-vivo to straw treated with too high a level of lime. This situation is similar to that of NaOH treatment as reviewed by Ribeiro (1989) where an application level above 6% resulted in in-vivo digestibility and voluntary daily intake tending to level off or even decrease while the IVDMD continued to increase.

The discrepancy between the in-vivo digestibility and in-vitro or in-sacco results further indicate that 6% lime is too high a level to maintain favourable rumen conditions for actual rumen degradation, although it can highly improve degradability/ fermentability of straw as a substrate. As previously shown (Nguyen Xuan Trach et al 2001), the rate of in-sacco degradation of hay as a standard substrate was lower when the animals were fed on 6% compared to 3% lime or urea-treated straws. The similar apparent digestibility and VFA content that resulted from feeding 6% and 3% lime-treated straws have probably been a reflection of a compromise between the highly increased degradability of straw and the less favourable rumen conditions associated with 6% lime. Unpalatability of straw treated with too high a level of lime (6%) may be a possibility for reduction in voluntary intake of the straw (Hove personal communication,  2000). However, a reasonable level of lime may improve straw palatability due to an effect of lime in reducing oxalates (Mudgal et al 1996).

Information is limited to elucidate why 6% lime did not have more positive effects on straw intake and in-vivo digestibility compared to 3% lime.  In general, high concentrations of dietary calcium are tolerated well by cattle (NRC 1996), and most of the additional calcium is excreted in the faeces (Djajanegara et al 1984). However, Ammerman et al (1963) have reported that protein and energy digestibility were reduced when cattle were fed a diet containing 4.4% Ca. In addition, Alfaro et al (1988) have also found some negative effects of high dietary Ca (2.35%) on metabolism of phosphorus, magnesium and certain trace elements, although the changes were relatively small. Although ruminants can tolerate wide Ca: P ratios (Call et al 1978), a ratio of Ca: P higher than 7:1 has been reported to reduce growth and feed efficiency (Wise et al 1963; Ricketts et al 1970). Another possible cause for 6% lime being no better than 3% lime is that a larger effect of a high lime level on straw cell wall degradability may, at the same time, be offset by a stronger effect on the lignin molecule to release phenolic acids, which are toxic to rumen microbes (Akin et al 1988; Chaudhry 2000).  

Whatever the reasons may have been, since 6% lime is not superior to 3% lime in increasing straw intake and digestibility and if a maximum tolerable concentration of Ca in feed for beef cattle is 2% as indicated by NRC (1984), a level of 3% lime should be maximum for rice straw treatment. However, further research in this area is needed before a firm conclusion can be made.

 

Conclusions

Based on the present study, 3% lime should be used in combination with urea to ensure the overall effectiveness of straw treatment. The additive effects of lime and urea on apparent digestibility of straw create the possibility that lime and urea can be used in combination as alkalis for treatment together with NPN and Ca supplementation of rice straw.


Acknowledgments

The authors would like to thank the Norwegian Council of Universities' Committee for Development Research and Education (NUFU) for the financial support to the present study. Special thanks are extended to Dr. Frik Sundstøl, Dr. Le Viet Ly, and Dr. Nils Petter Kjos for their facilitation and advice during the experimentation and manuscript preparation.

 

References

Akin D E, Rigsby L L, Theodorou M K and Harley R D 1988 Population changes of fibrolytic bacterium in the presence of phenolic acids and plant extracts. Animal Feed Science and Technology. Volume 19: 261-275.

Alfaro E, Neathery M W, Miller W J, Gentry R P, Crowe C T, Fielding A S, Etheridge R E, Pugh D G and Blacmon D M 1988 Influence of a wide range of calcium intakes on tissue distribution of macroelements and microelements in dairy calves. Journal of Dairy Science. Volume 71: 1295-1300.

Ammerman C B, Arrington L R, Jayaswal M C, Shirley R L and David G K 1963 Effect of dietary calcium and phosphorus levels on nutrient digestibility by steers. Journal of Animal Science. Volume 22: 248 (abstr.).

Burns J C, Pond K R and Fisher D S 1994 Measurement of forage intake. In Fahey G F Jr (ed.) Forage Quality, Evaluation, and Utilization. Madison. Wisconsin. USA. pp 494-532.

Call J W, Butcher J E, Blake J T, Smart R A and Shape J L 1978 Phosphorus influence on growth and reproduction of beef cattle. Journal of Animal Science. Volume 47: 216-225.

Chaudhry A S 1998 Nutrient digestion and rumen fermentation in sheep of wheat straw treated with calcium oxide, sodium hydroxide and alkaline hydrogen peroxide. Animal Feed Science and Technology. Volume 74: 315-328.

Chaudhry A S 2000 Rumen degradation in-sacco in sheep of wheat straw treated with calcium oxide, sodium hydroxide and sodium hydroxide plus hydrogen peroxide. Animal Feed Science and Technology. Volume 83: 313-323.

Chenost M and Kayouli C 1997 Roughage Utilization in Warm Climates. FAO Animal and Health Paper 135. Rome.

Chermiti A, Teller E, Vanbelle M, Collignon G and Matatu B 1994 Effect of ammonia or urea treatment of straw on chewing behavior and ruminal digestion processes in non-lactating dairy cows. Animal Feed Science and Technology. Volume 47: 41-51.

Cochran R C and Galyean M L 1994 Measurement of in-vivo forage digestion by ruminants. In Fahey G F Jr (ed.) Forage Quality, Evaluation, and Utilization. Madison. Wisconsin. USA. pp 613-643.

Cunniff P (ed.) 1997 Official Methods of Analysis of AOAC International. Maryland. USA.

Djajanegara A and Doyle P T 1989 Urea supplementation compared with pretreatment. 1. Effects on intake, digestion and live-weight change by sheep fed a rice straw. Animal Feed Science and Technology. Volume 27: 17-30.

Djajanegara A, Molina B T and Doyle P T 1984 The utilization of untreated and calcium hydroxide treated wheat straw by sheep. Animal Feed Science and Technology. Volume 12: 141-150.

Doyle P T, Devendra C and Pearce G R 1986 Rice straw as a feed for ruminants. International Development Program of Australian Universities and Colleges Limited (IDP). Canberra.

Jayasuriya M C N, Haminton R and Rogovic B 1987 The use of an artificial rumen to assess low quality fibrous feeds. Biological Wastes. Volume 20: 241-250.

Madrid J, Hernandez F, Pulgar M A and Cid J M 1997 In-vivo digestibility of treated and untreated barley straw: results of direct and by-difference digestibility trials. Animal Feed Science and Technology. Volume 65: 129-138.

Males J R 1987 Optimizing the utilization of cereal crop residues for beef cattle. Journal of Animal Science. Volume 65: 1124-1130.

Mertens D R 1994 Regulation of forage intake. In Fahey G F Jr (ed.) Forage Quality, Evaluation, and Utilization. Madison. Wisconsin. USA. pp 450-493.

Misra A K, Agrawal I S and Verma M L 1995 Effect of restricted feeding of urea treated wheat and rice straws on nutrients intake and digestibility. Indian Journal of Animal Nutrition. Volume 12: 222-224.

Mudgal P L, Bhadoria H B S and Singh P V 1996 Utilisation of koha (Terminalia arjuna) fruits for livestock feeding. Indian Journal of Animal Nutrition. Volume 13: 103-104.

Nguyen Xuan Trach, Mo M and Cu Xuan Dan 2001 Effects of treatment of rice straw with lime and/or urea on its chemical composition, in-vitro gas production and rumen degradation. (Submitted to LRRD).  

NRC 1984
. Nutrient requirements of beef cattle (6th revised ed.). National Academy Press. Wahington, D.C.

NRC 1996. Nutrient requirements of beef cattle (7th revised ed.). National Academy Press. Wahington, D.C.

Ørskov E R 1994 Recent advances in understanding of microbial transformation in ruminants. Livestock Production Science. Volume 39: 53-60.

Ørskov E R 1998 Feed evaluation with emphasis on fibrous roughages and fluctuating supply of nutrients: A review. Small Ruminant Research. Volume 28: 1-8.

Preston T R 1995 Tropical Animal Feeding - A Manual for Research Worker. FAO Animal Production and Health Paper 126. Rome. [http://www.fao.org/ag/aga/agap/frg/AHPP126/cont126.htm]

Rai S N and Mudgal V D 1988 Feeding treated straw for efficient utilization and production by Murrah buffaloes. Buffalo Journal. Volume 2: 161-172.

Ribeiro J M C R 1989 Intake measurement. In Chenost M and Reiniger P (Eds.) Evaluation of  Straws in Ruminant Feeding. Elsevier. Amsterdam. pp 22-35.

Ricketts R E, Campbell J R, Weinman D E and Tumbleson M E 1970 Effect of three calcium: phosphorus ratios on performance of growing Holstein steers. Journal of Dairy Science. Volume 53: 898-906.

Saadullah M, Haque M & Dolberg F 1981 Treatment of rice straw with lime. Tropical Animal Production. Volume 6 No. 2, 116-120   [http://www.fao.org/ag/aga/agap/frg/tap62/62_116.pdf]

Sahoo B, Saraswat M L, Haque N and Khan M Y 2000 Energy balance and methane production in sheep fed chemically treated wheat straw. Small Ruminant Research. Volume 35: 13-19.

SAS 1996 SAS User’s Guide: statistics (Version 6 Ed.). SAS Institute Inc. USA.

Schiere J B and Ibrahim M N M 1989 Feeding of urea-ammonia treated rice straw. Pudoc. Wageningen. Netherlands.

Schiere J B and Nell A J 1993 Feeding of urea treated straw in the tropics. I. A review of its technical principles and economics. Animal Feed Science and Technology. Volume 43: 135-147.

Selvendran S A, Matsuoka S, Fujita H and Harishume T 1977 Study on the improvement in the feeding value of rice straw. Research Bulletin. Obihiro University. Japan. Volume 10: 447-459.

Silva A T and Ørskov E R 1988 Fiber digestion in the rumens of animals receiving hay, untreated or ammonia treated straw. Animal Feed Science and Technology. Volume 19: 299-287.

Singh S P and Gupta B N 1988 Total volatile fatty acid and bacterial production rates as affected by rations containing untreated or ammoniated straw with or without impregnation of urea and molasses. Indian Journal of Animal Nutrition. Volume 5: 291-295.

Silva A T and Ørskov E R 1988 Fiber digestion in the rumens of animals receiving hay, untreated or ammonia treated straw. Animal Feed Science and Technology. Volume 19: 299-287.

Sundstøl F and Coxworth E M 1984 Ammonia treatment. In Sundstøl F and Owen E C (Eds.) Straw and Other By-products as Feed. Elsevier. Amsterdam. pp 196-247.

Van Es A J H 1978 Feed evaluation for ruminants. I. The systems in use from May 1977 onwards in the Netherlands. Livestock Production Science. Volume 5: 331-345.

Van Soest P J and Robertson J B 1985 Analysis of Forages and Fibrous Foods. A Laboratory Manual for Animal Science 613. Cornell University. USA.

Weiss W 1994 Estimation of digestibility of forages by laboratory methods. In Fahey Jr G F (ed.) Forage Quality, Evaluation, and Utilization. Madison. Wisconsin. USA. pp 644-681.

Wise M B, Ordoreza A L and Barrick E R 1963 Influence of variation in dietary calcium: phosphorus ratio on performance and blood constituents of calves. Journal of Nutrition. Volume 79: 79-86.

Zaman M S and Owen F 1990 Effect of calcium hydroxide or urea treatment of barley straw on intake and digestibility in sheep. Small Ruminant Research. Volume 3: 237-248.

Received 20 July 2001

Go to top