Effect of different strategies of processing rice straw on in vitro digestibility using rumen fluid or faecal inocula of local cattle

Nguyen Van Thu

Cantho University
nvthu@ctu.edu.vn

Abstract

Two experiments were carried out to evaluate effect of different treatments of rice straw on in vitro digestibility using faecal and rumen d inocula from local cattle fed natural grasses. In two complete randomized design experiments, there were 6 treatments and 3 replicates. The treatments included: fresh rice straw (FS), fresh rice straw treated by 1.5% urea (UFS), fresh straw with added urea-molasses-mineral mixture (FS+UMM), dry rice straw (S), urea-treated (5%) dry rice straw (US); and dry rice straw with added urea-molasses-mineral mixture (US+MM). The first experiment was done using rumen fluid as inoculum, while in the second one faeces were used as the microbial source.

Adding urea, molasses and minerals to rice straw increased content of nutrients and in vitro digestibility values. There was a close relationship between in vitro digestibility parameters determined with rumen fluid and and with faecal inocula (R²= 0.92).

It is concluded that the nutritive value of rice straw for cattle is improved by adding urea, molasses and minerals; and that faecal inocula can be used to evaluate in vitro feed digestibility, with reduced cost and improved animal welfare.

Key words: Rice straw, urea-molasses-mineral mixture, in vitro digestibility, rumen fluid, faeces, inoculum

Introduction

In recent years a number of Mekong delta (MD) provinces of Vietnam have had programs of ruminant development to satisfy the human meat and milk demand due to a serious reduction of the ruminant population. Rice straw is considered to be a main coarse feed for the large ruminants in MD, because rice production area is largely increasing, while grassland area is narrowing. However, rice straw has low nutritive and digestibility values. Feeding ruminants with rice straw only will cause a live weight and health loss (Nguyen Van Thu et al 1991). In the Mekong delta, when rice is harvested during the rainy season, the straw is mostly used for fertilizer due to spoilage. Taher (2000) reported that rice straw enriched by adding a urea-molasses mixture has a great potential a feed resource.

Recent studies on in vitro digestibility and gas production techniques have shown that faecal inocula has promise in replacing rumen fluid (Ly et al 1997 and El-Meadaway et al 1998) due to lower cost and no need to have available surgically modified animals thus responding to issues of animal welfare.

This study therefore had two objectives: to investigate different strategies for processing wet season and dry season rice straw; and to determine whether faecal inocula can be used as a microbial source for determining in vitro OM digestibility.

Materials and methods

In two completely randomized designs, there were 6 treatments and 3 replicates. The treatments were: fresh (wet season) rice straw (FS), fresh rice straw treated by 1.5% urea (UFS), fresh rice straw with added urea-molasses-mineral mixture (FS+UMM), dry rice straw (S), urea-treated (5%) dry rice straw (US); and dry rice straw with added urea-molasses-mineral mixture (US+MM). The first experiment was done using rumen fluid as inoculum, while in the second one faeces were used as the microbial source. The fresh rice straw after being harvested was immediately brought to the laboratory for drying at 60^oC for later analysis. The urea-molasses mineral mixture included (%): urea 1.4 and molasses and minerals 5.7 (fresh matter basis). The S+UMM was rice straw to which was added a mixture of 3.2% urea and 14.3% molasses and micro-minerals. The FS and S were treated with urea, after 21 days they were used for analysis.

The in vitro OM digestibility determination followed the procedure of Goering and Van Soest (1970) as modified by Mbwile and Udén (1991). Rumen fluid was collected by suction using a 1-cm diameter tube at 7.00 h. It was strained to remove the feed particles. Faeces were collected from animals by rectal grab sampling at the same time. The semi-solid faeces were diluted (300g of fresh feces to 1.5 litres of reduced medium), mixed by hand and the resultant slurry strained as for the rumen fluid.

The three cattle used for the in sacco method were fed natural grasses. In both experiments, the feed samples were dried at 105^oC overnight to determine dry matter (DM). The OM was determined by ashing samples in a furnace at 500^oC for 4 h. The crude protein was determined by the Kjeldahl method (AOAC 1980). Analysis of neutral detergent fiber (NDF) was by a method described by Van Soest et al (1991). Acid detergent fiber (ADF) was analyzed by the method suggested by Robertson and Van Soest (1981).

The experimental data were subjected to analysis of variance (ANOVA) using the General Linear Model (GLM) procedure of Minitab (1998). When the F test was significant (P<0.05), Tukey’s test for paired comparison was used to separate the means. In the comparison of in vitro degradability values between rumen fluid and faecal inocula, data were analyzed using the paired "t" test and regression software of Minitab (1998).

Results and discussion

Differences in chemical composition of the samples of rice straw reflect the effects of urea treatment and of the added urea-molasses (Table 1). The crude protein appeared to be lower in the fresh straw (FS) than in the stored material (S); however, this was not reflected in the urea-treated and supplemented straws where CP values were always higher for the stored straw.

Table 1: Chemical composition of rice straw with and without treatment (DM basis except for DM which is on fresh basis)
	FS	UFS	FS+UMM	S	US	S+UMM
DM	90.0	89.1	89.1	89.8	84.1	87.9
OM	88.3	87.5	88.2	87.8	88.0	88.4
CP	8.4	10.3	12.8	6.8	13.3	14.4
NDF	62.5	65.6	57.2	63.7	60.2	54.2
ADF	36.6	38.9	36.5	37.2	37.8	35.6
Ash	11.7	12.5	11.8	12.2	12.0	11.6
FS: fresh rice straw, UFS: urea-treated fresh rice straw, FS+UMM: fresh rice straw + urea-molasses mineral mixture, S: rice straw, US: urea-treated rice straw, S+UMM: rice straw+ urea-molasses mineral mixture

In general, urea treatment of the straws, and supplementation with urea-molasses-minerals, led to improvements in in vitro OM digestibility (Table 2). These results are similar to those reported by Chowdhury and Huges (1998) for addition of urea-molasses to rice straw. It seemed that with the faecal inocula, at least 96hr were needed to reach the maximum values. Solangi (1997) also found that at least 96h incubation was necessary before digestion of straw reached its asymptote.

Table 2. In vitro OM digestibility (%) of rice straw with and without treatment using faecal inocula from cattle
Incubation time (h)	FS	UFS	FS+UMM	S	US	S+UMM	Prob.
12	23.5^ab	29.1^bc	30.9^cd	19.1^a	25.5^abc	31.7^cd	0.001
24	27.7^ab	30.0^ab	33.6^bc	25.4^a	28.1^ab	35.9^c	0.001
48	33.8^ab	36.1^bc	34.9^b	29.4^a	35.3^ab	40.3^c	0.001
72	37.7^ab	39.7^ab	42.1^b	34.2^a	42.4^b	41.5^b	0.001
96	45.2	44.5	48.0	44.3	48.4	48.2	NS
FS: fresh rice straw, UFS: urea-treated fresh rice straw, FS+UMM: fresh rice straw + urea-molasses mineral mixture, S: rice straw, US: urea-treated rice straw, S+UMM: rice straw+ urea-molasses mineral mixture abcd Means without letter in common within the same row are different at P<0.05

The in vitro digestibility values using rumen fluid as inoculum were higher than the corresponding values using faeces as the inoculum (Tables 2 and 3). However, the two sets of data were closely related (R² = 0 0.86; Figure 1). Similar results were reported by Ahkter and Hossain (1998) and El-Meadaway et al (1998). The lower values obtained with the faecal inoculation are likely to be due to lower a lower fibrolytic bacteria population in faecal liquor compared to that in the rumen fluid (Kumar et al 1999). It is likely that the onset of the fibre fermentation is delayed when using faeces as inoculum.

Table 3. In vitro OM digestibility values (%) of rice straw with and without treatment, using rumen fluid inocula from cattle
Incubation time (h)	FS	UFS	FS+UMM	S	US	S+UMM	Prob.
12	32.4^a	30.7^a	41.6^b	30.7^a	33.4^ab	40.7^b	0.001
24	40.9^ab	41.6^ab	47.1^b	36.5^a	45.9^b	45.9^b	0.001
48	51.1^ab	54.9^ab	56.8^b	48.2^a	57.4^b	56.2^b	0.01
72	56.4^a	61.1^b	62.1^b	55.1^a	63.5^b	61.5^b	0.01
96	58.1^a	64.1^ab	66.7^b	58.5^a	66.4^b	65.7^b	0.001
FS: fresh rice straw, UFS: urea-treated fresh rice straw, FS+UMM: fresh rice straw + urea-molasses mineral mixture, S: rice straw, US: urea-treated rice straw, S+UMM: rice straw+ urea-molasses mineral mixture abcd Means without letter in common within the same row are different at P<0.05

Figure 1. Relationship between in vitro OMD values of rice straw determined
with rumen fluid or faeces as inocula

Conclusions

Ading urea, molasses and minerals to rice straw increased the nutrient content and the in vitro digestibility.
Faeces can be used as microbial source for determining the in vitro degradability of rice straw

Acknowledgements

This research was partially financed by the bilateral SAREC 2000-2002 project.

References

Akhter S and Hossain M M 1998 Cow faeces in in vitro digestibility assays of forages. Asian-Aust. J. of Anim. Sci. 11: 51-54.

Chowdhury S A and Huque K S 1998 Effect of molasses or rice gruel inclusion to urea supplemented rice straw on its intake, nutrient digestibilities, microbial N yield, N balance and growth rate of native (Bos indicus) growing bulls. Asian-Aus. J. Anim. Sci. 1998. Vol. 11, 145-151.

El-Meadaway A, Mir Z, Zaman M S Yanke L J 1998 Relative efficacy of inocula from rumen fluid and faecal solution for determining in vitro digestibility and gas production. Can. J. Ani. Sci. 78: 673-679.

Ly J, Nguyen Van Lai, Rodriguez L and Preston T R 1997 In vitro gas production and washing losses of tropical crop residues for ruminants and pigs. Livestock Research for Rural Development (13) 4: http://www.cipav.org.co/lrrd/lrrd9/4/ly941.htm

Kumar S, Gupta B S Yadav K R 1999 Effect of different roughage protein and energy sources on in vitro rumen fermentation using rumen and dung liquor inoculant. Indian J. Ani. Nutr. 16, 112-116.

Nguyen Van Thu and Udén P 2003 Feces as an alternative to rum fluid for in vitro digestibility measurement. Buffalo Journal. Vol 19. No. 1. 4/2003 .Thailand (in press).

Solangi A A 1997 Studies on the use of fecal organisms in the in vitro assessment of forages. PhD thesis. University of Wales, Bangor, UK.

Schiere J B, Ibrahim M N M, Sewalt V J H and Zemmelink G 1989 Response of growing cattle

given urea-treated and untreated rice straw to supplementation with rice bran and lick blocks

containing urea and molasses. Animal Feed Science and Technology. No. 26: 179-189.

Taher S 2000 Rice straw feeding – difficulties and results. FAO Buffalo Newslettter. 14, 10-13.

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