Rumen environment and digestibility on rice  straw alone or supplemented with native grass

 

Nguyen Van Hon, Nguyen Trong Ngu and Nguyen Thi Hong Nhan

                   College of Agriculture, Cantho University

Abstract

The aim of this work was to assess whether feeding some grass along with rice straw would improve the digestibility by enhancing the rumen environment. A completely randomized block design was used with four Yellow x Sindhi rumen-fistulated cattle and five treatments including only grass (G), rice straw (RS), grass with rice straw (GRS), grass with 4% urea treated rice straw (GTRS) and grass with with 4% urea-sprayed rice straw (GSRT). There were differences (P<0.001) in dry matter (DM) intake and DM digestibility (DDM) ranging from 1.93 to 5.21 kg DM/day for “G” and “RS”, respectively. A similar trend was recorded for DDM (from 56.4 to 74.0%). Rumen fluid was collected before and 2 and 6 hours after feeding.  Ammonia-N at 2 hours increased (P<0.001) up to 317mg/litre on the GSRT diet while the protozoa population decreased.

Key words: cattle, urea, rice straw, natural grass, digestibility, rumen environment, protozoa, ammonia

 

Introduction

The use of ammonia to upgrade rice straw and other low quality roughages for feeding ruminants has attracted considerable attention in recent years (Sundstol et al 1984). Much research has been done on ammonia-treated rice straw to find the best way of utilization of this abundant resource. It seemed to be successful on-station but limited in its impact with farmers although ammonia can be found in form of urea, which is affordable. Spraying urea at 4% directly on the rice straw will hopefully bring about similar effect and hell reduce labor cost and make the work simpler.

 

It is known that rice straw is slowly and partially degraded in the rumen particularly when no supplement is offered. Also, low metabolic function due to imbalanced nutrients will contribute to low feed intake (Schiere and Ibrahim 1989). To optimize rumen function, natural grass was added to improve the digestion of Sisal pulp, a fibrous agricultural by-product (Guttierrez and Elliott 19--).

 

Hence, the hypothesis to be tested was:

·        Supplementing a basal diet of treated/untreated rice straw with grass will increase the digestibility of the basal diet and improve animal performance.

The objectives of the study were to add grass to rice straw treated by different methods and test the effect on:

·        The rumen environment

·        DM digestibility

·        The degradability rate of Brachiaria multica and Sacciolepis interrupta

 

Materials and methods

Location, animals and housing.

The experiment was done at the experimental farm of Cantho University with four crossbred Yellow-Sindhi cattle from 1.5 to 2 years old and fitted with rumen cannulas. The animals were placed in individual stalls and clean and fresh water was offered ad libitum for the whole period of study.

Experimental design

The experiment was arranged in a 5*4 completely randomized block design of which animals were considered as blocks and five diets understood as treatments. Each period consisted of 15 days of adaptation followed by 5 days of sample collection.

Feeding management and measurements

The diets comprised:    

·        Grass (G),

·        Rice straw (RS),

·        Grass with rice straw (GRS)

·        Grass with 4% urea-treated rice straw (GTRS)

·        Grass with with 4% urea-sprayed rice straw (GSRT).

 

For GRS, GTRS and GSRT, the grass supplied 50% of the dry matter of the diet.  Feeds were  offered 4 times per day for stimulating intake and reducing refusal. The offer and refusals were weighed daily and analyzed on the last five days. Faeces were collected daily and frozen until the time of doing the analysis.

 

Rumen fluid was taken before feeding and 2 hours and 6 hours after feeding. Measurements included pH, ammonia concentration (Kjeldahl distillation) (AOAC 1990) and populations of protozoa (direct counting under microscope).

 

The four cattle were maintained on each feeding regime for two weeks at the end of which milled sub-samples were incubated in nylon bags in their rumens and removed at  12, 24 and 48  hours using the procedures recommended by Ørskov and Shand (1995).

Statistical analysis

Data were analyzed by Minitab software version 11.2 using the General Linear Model òf the ANOVA programme.

 

Results and discussion

Feed intake and DM digestibility

 

The diets of grass and rice straw reflected the extreme responses of dry matter intake (5.2 and 1.9 kg/d) with the other treatments having intermediate levels (Table 1). When the cattle were fed the grass supplement intakes were similar on the diets with treated, sprayed and untreated rice straw. This is not in line with the statement given by Schiere and Ibrahim that urea treatment leads to increases in DM intake of  20-40%.  The high rate of substitution of the straw by the grass may have masked the effects of the urea treatment.

 

pH, ammonia-N concentration and protozoa in the rumen

 

The pH value was highest (7.35) when cattle were fed rice straw (Table 2), and gradually decreased to 7.12, 7.1 and 7.08 on the grass and straw diets, with the lowest value on grass alone (6.8). It can be explained by higher soluble carbohydrates present in grass making it prone to higher volatile fatty acid production, which is partly responsible for low pH. Additionally, it took a longer time for the pH to decline as compared to the report made by Hungate (1966).

 

Rumen ammonia levels were lower on rice straw alone than on any of the combinations of straw and grass (P<0.001), with a tendency to be highest on straw sprayed with urea. A suggested minimum rumen level of ammonia of 150mg/litre was proposed by Preston and Leng (1987), thus the diet only of rice straw was greatly deficient in supplying nitrogen to rumen microbes. The data from Table 2 also showed improved ammonia-N concentration after feeding, according to the nitrogen contained in feed being rapidly degraded, and then remaining constant.

 

Protozoa are known to take part in metabolizing bacterial and dietary nitrogen extensively, and contribute to the total rumen nitrogen. The protozoa population (Table 2) was affected (P<0.001) by treatments. Lowest number of protozoa (0.42x10⁵/ml) were on the rice straw diets without  grass, rising to 1.46, 1.58 and 1.1 on the straw plus grass diets with the highest value on grass alone (2.1 x 10⁵/ml).  The latter result is almost certainly due to the presence of soluble carbohydrates in the fresh grass.

 

Effects of treatments on in sacco degradability of feeds in the rumen

 

Table 3. Relative degradability at 12, 24 and 48 hours of reference feeds in the rumen of cattle.
Substrate							SEM/P
		GRS	GTRS	GSRS	G	RS
Rice straw	12h	9.5	13.4	12.6	14.8	9.6	1.09/0.013
	24h	17.7	23.7	19.0	24.0	13.4	1.8/0.004
	48h	34.9	40.9	41.1	47.6	20.6	1.78/0.001
S. interrupta	12h	19.9	22.1	19.0	19.5	15.5	1.18/0.02
	24h	29.6	30.8	26.9	25.7	17.7	1.9/0.002
	48h	50.8	56.0	46.6	46.6	27.1	2.95/0.001
B.mutica	12h	21.2	22.4	20.7	19.7	14.3	1.93/0.076
	24h	31.9	32.4	30.9	28.7	17.6	2.9/0.016
	48h	46.9	48.5	51.0	50.0	24.7	3.7/0.001

 

Sacciolepis interrupta and Brachia multica were more highly degraded in sacco than rice straw at all times of incubation (Table 3). The rumen environments created by the grass and grass plus straw diets supported faster degradability of the reference feeds that the diet of rice straw alone.

 

Conclusion

It can be concluded from this work that spraying urea directly to rice straw brings similar response of intake, DM digestibility, ruminal ammonia-N level and ability to stimulate activities of microbes as that provided by urea-treated rice straw. A visible advantage of this method is the simplicity making it easy to apply in farmers’ conditions. Sacciolepis interrupta and Brachia multica growing in acid sulfate regions in the Mekong Delta also proved their potential as a source of feed for cattle. Fresh grass and combinations of grass and rice straw provided a better rumen environment for digestion of reference feeds of rice straw and local grasses compared with rice straw alone.

 

Acknowledgements

I wish to thank the SAREC Project  for funding the research which has resulted into this publication.

 

References

 

AOAC 1990 Official methods of analysis of the Association of Official Analytical Chemist (15^th Edn), Washington, DC. 1: 69-90.

 

Guttierrez E and Elliott R 1984 Interaccion digestiva de la pulpa de henequen (Agave fourcroydes) y el pasto Estrella de Africa (Cynodon plectostachyus). Altenativas y Valor Nutritivo de Algunos Recursos Alimenticios Destinados a Produccion Animal. Informe Provisional No 16. Fundacion Internacional para la Ciencia. Stockholm   (16) :229-246

 

Hungate R E 1966 The rumen and its Microbes. Academic Press. New York.

 

Ørskov E R and Shand W 1995 Use of nylon bag technique for protein and energy evaluation and for rumen environment studies in ruminants. Livestock Research for Rural Development. Volume 9(1).

 

Preston T R and Leng R A, 1987 Matching ruminant production systems with available resources in the tropics and sub-tropics. Penambul books. Armidale, Australia

 

Schiere J B and Ibrahim M N M 1989. Feeding of urea-ammonia treated rice straw. A compilation of miscellaneous reports produced by the Straw Utilization Project (Sri Lanka): 9, 101

 

Sundstol F, Coxworth E and Mowat D N 1984 Improving the nutritive value of straw and other low-quality roughages by treatment with ammonia. World Animal Review 26: 13-21.

 

 

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