Study on processing and utilizing rice straw as a feed resource
for sheep in North Vietnam
 

Khuc Thi Hue, Nguyen Thi Mui, Do Thi Thanh Van,
Dinh Van Binh and T R Preston
 

Goat and Rabbit Research Center, Sontay, Hatay, Vietnam
binhbavi@netnam.vn

 Abstract

 

A total of 60 sheep with an initial weight of 16 to 21 kg and ages ranging between 4.5 and 5 months were allocated to 6 treatments:  untreated rice straw (control);  rice straw + 20% molasses; rice straw + 1% urea; rice straw + 1% urea + 20% molasses\;  urea-treated rice straw; urea-treated rice straw + 20% molasses.  Measurements were made of in vitro gas production of the straws and the growth and feed conversion of the sheep fed the different types of rice straw ad libitum plus 125 g/day dry cassava roots and 125 g/day rice bran.

 

Rate of gas production was increased by treating the straw with urea (a+b = 57.3 ml vs 39.8 ml for urea-treated and untreated straw). Adding molasses to the untreated straw increased the intake from 150 to 310 g DM/day. Adding molasses to the rice straw plus urea treatment increased the intake from 168 to 362 g DM/day but molasses addition had no effect on intake of the urea-treated straw (269 and 273 g DM/day.  The sheep lost weight on untreated straw without (-11 g/day) or with molasses (-2 g/day). Best performance was with urea-treated rice straw plus molasses (37 g/day), which was better than urea-treated straw without molasses (15 g/day). Untreated straw with added urea and molasses supported a growth rate of 25 g/day.  Feed conversion data were in the same order as the growth rates.

 

It can be concluded that urea-treatment plus supplementary molasses is the best way to offer rice straw to growing sheep.

 

 Keywords: Urea-treated rice straw, molasses, gas production, sheep
 

 

Introduction

 

Sheep have been raised in the Phan Rang area in central Vietnam for a long time. The sheep were imported originally from Mongolia and China and are commonly called the Phan Rang breed. They are used for meat production only. The population of sheep in Phan Rang was around 3000 in 1996 and has reached today about 16,000. In 1999, 60 sheep were moved from Phan Rang to the Goat and Rabbit Research Centre in northern Vietnam to develop sheep production systems in this area. The sheep have now adapted to the environment and the population has increased to over 300. The sheep have also been introduced to farmers in the Bavi district.  The major constraint to developing sheep production in the area is the shortage of feed in the dry season,  because at this time most of the grasses are very difficult to grow and using concentrate is too expensive for poor farmers.        

 

Vietnam is a major rice producing country. As a result, rice straw is available in large quantities (ca. 18 million tonnes per year). Many researchers have studied methods to improve the nutritional value of this roughage (Chenost and Kayouli 1997). But this work has  focused mainly on large ruminants. There is no report on using rice straw for sheep production in Vietnam although positive results are reported from China using ammonium bicarbonate to "ammoniate" the straw (Liu et al 1998). Rice straw is the main feed for cattle and buffaloes in the dry season in North Vietnam but there is no experience of feeding this resource to sheep. 

 

Spraying urea on the straw or ensiling the straw with urea (urea-treatment) are the common methods of increasing the nutritive value. The aim of this study was to compare these two methods, with or without supplementary molasses, as the basal diet for growing sheep.

 

Hypothesis of the study

• When rice straw is treated with urea, the nutritive value and gas production will be improved.

•  Addition of 20 % of molasses to rice straw treated, or supplemented, with urea in the diet will increase feed intake and live weight gain of growing sheep
   

 

Materials and methods

 

In vitro gas production

 

Two rumen-fistulated cows were used to collect rumen fluid. They were fed close to their energy maintenance feeding level with a diet consisting of grasses and concentrate. Rumen fluid was collected 2 h after the morning feeding into a pre-warmed thermos filled with CO₂ and was strained and filtered through cheese-cloth and mixed (1:2 v/v) with an anaerobic buffer/mineral solution. About 200 mg dry weight of rice straw and urea-treated rice straw were incubated with 30 ml of  buffered rumen fluid in 100 ml calibrated syringes and placed in a ventilated incubator at 39 ^ºC. The syringes were gently shaken 30 min after the start of incubation and then every hour for the first 10 h of incubation (Menke et al 1979). Readings were recorded before incubation and 3, 6, 12, 24, 48, 72 and 96h after incubation. The results of gas volume readings were fitted to the exponential equation of the form p=a+b(1-e^-ct) ( McDonald 1981)  where 'p' represents gas production at time 't', 'a+b' the potential gas production, 'c' the rate of gas production and 'a', 'b' and 'c' are constants in the exponential equation. Apparent organic matter digestibility (OMD) of the rice straw and urea-treated rice straw was estimated from the volume of gas produced (GP=ml) after 24 h of incubation and the proportion of crude protein (CP = g/kg DM) following the equation of Menke et al 1979):
 

OMD (%)=24.91 + 0.7222GP + 0.0815CP

 

Feeding trial 

A completely randomized design was used with 60 sheep (initial weight 16 to 21 kg; age 4.5 to 5 months) allocated to the following six treatments (6 males and 4 females per treatment):

• RS: Untreated rice straw (control)

• RSM: Rice straw + 20% molasses

• RSU: Rice straw + 1% urea

• RSMU: Rice straw + 1% urea + 20% molasses

• UTRS: Urea-treated rice straw (2.5% urea; 0.5% lime; 0.5% salt)

• UTRSM: Urea-treated rice straw + 20% molasses

In addition to the rice straw, the sheep were given 125 g/day of dry cassava roots and 125 g/day of rice bran. The rice straw was chopped into pieces from 4 to 7 cm length before feeding or processing. Urea-treated rice straw was prepared by using 2.5 kg urea + 0.5 kg lime + 0.5 kg salt, mixing with 100 kg rice straw and 100 kg water then covering for 10 days before feeding. The urea-supplemented rice straw was prepared by spraying the rice straw, prior to feeding,  with a solution of 1 kg urea + 100 kg water per 100 kg rice straw.  The rice straw was fed ad libitum. For treatments RS and RSM, water was mixed with the straw to give a similar dry matter content as for the other treatments. The sheep were weighed at the beginning and every 10 days after the experiment started.

Chemical analysis

Samples of feeds offered and refused were taken daily, dried at 60 ºC and stored. Every 4 weeks the samples were analysed for DM and crude protein according to the standard methods of AOAC (1990).  NDF and ADF were determined by the methods of Van Soest et al  (1991).

Statistic analysis 

The data from the experiments were analysed using one-way analysis of variance (Minitab 1998). The treatment means which showed significant differences at the probability level of P<0.05 were compared using the Fisher pair-wise comparisons procedure.  The model used in the analysis of the data from the feeding trial was:

Y = m+ T + e

 

where Y = the dependent variable, m = the general mean, T  =  the effect of the treatment and e  = the random error effect.
 

 

Results and discussion

 

The straw that was supplemented (RSU), or treated (UTRS and UTRSM), with urea had almost twice the level of crude protein as the untreated (RS)\ or molasses-supplemented straw (RSM) (Table 1).

 

Rates of gas production after 72 and 96 h were higher for UTRS than for RS (Table 2) resulting in a 22%  increase in the predicted organic matter digestibility (Table 3).

 

Table 3: Gas production characteristics of RS and UTRS and predicted organic matter digestibility
	a	b	a+b	c	Lag time, h	RSD	OMD (%)
RS	-3.7	44.3	39.8	0.0182	5.6	1.94	57.2
UTRS	-3.2	61.2	57.3	0.0121	5.7	1.74	69.7

       

Addition of molasses, but not of urea, increased the intake of untreated straw DM (Table 4). Addition of molasses had no effect on DM intake when the straw was treated with urea and lime. The sheep lost live weight on untreated rice straw or untreated straw supplemented with molasses (Figure 1). They maintained weight on the straw supplemented with urea and lime. Growth rates were improved when the rice straw was supplemented with urea plus molasses (25 g/day) and was highest for urea-treated rice straw plus molasses (37 g/day). Straw treated with urea/lime supported a growth rate of 15 g/day. The best feed conversion was with urea-treated straw supplemented with molasses.

Table 4: Mean values for feed intake, live weight change and feed conversion
	RS	RSM	RSU	RSUM	UTRS		UTRSM	SEM
Feed DM intake, g/day
Rice straw	150a	309b	168a	362d	269c		273c	6.99
Cassava root	124	124	124	124	124	124		0.14
Rice bran	124	122	124	115	125		119	0.92
Total	399 a	555 b	415 a	603c	518 b		516 b	6.96
Live weights, kg
Initial	16.9	20.7	16.8	16.1	19.4		19.2	1.74
Final	15.5	20.5	16.8	19.3	21.4		23.9	1.89
Weight change, g/day	-11 a	-2 a	0 a	25 b	15 ab		37 b	6.21
Feed DM conversion				24.8	34.7		13.5	1.64
abcd Means in the same row without letter in common are different at P<0.05

 

 

           

Figure 1: Changes in live weight of sheep fed untreated rice straw supplemented with urea or molasses
 or  urea-treated rice straw with or without molasses

 

 

Conclusions

Treatment of rice straw with urea/lime, or supplementation of untreated rice straw with urea and molasses, were necessary in order to support positive growth rates in sheep.

 

References

 

 

AOAC 1990 Association of Official Analytical Chemists. Official Methods of Analysis K Helrick, ed)  13th edition. Arlington pp 1018

 

Chenost M and Kayouli C 1997 Roughage utilization in warm climates. FAO Animal Production and Health Paper 135. FAO: Rome

 

Liu J, Chen Z, Yu J Q, Fei B R, Wang W D and Zhang J F 1998  Effect of ammonium bicarbonate treatment and rapeseed meal supplementation on growth rate of Huzhou lambs receiving rice straw. Livestock Research for Rural Development  (10) 2: http://www.cipav.org.co/lrrd/lrrd10/2/liu102.htm

McDonald E 1981 A revised model for the estimation of protein degradability in the rumen. Journal of Agricultural Science, Cambridge 96:251-252

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

Van Soest P J, Robertson J B and Lewis B A 1991. Methods for dietary fiber, neutral detergent fiber and non starch polysaccharides in relation to animal nutrition. Journal of Dairy Science 74:3583-3593

 

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