Biological Wastes 22 (1987) 229-232

Short Communication

Anaerobic Digestion as a Method of Determining Rumen Digestibility of Cellulosic Materials

I N T R O D U C T I O N

The digestibility of cellulosic materials can be best studied by undertaking trials on ruminants. However, these trials need large quantities of the materials, and this may become impracticable when a number of samples are to be tested. Mellenberger et al. (1970) suggested one in vitro method to determine rumen digestibility. Subsequently, Morris (1976) suggested a nylon bag technique to determine digestibility by suspending samples in bags in the rumen itself. Studies on some details of fibre digestion were done by Morris & Bacon (1977) and Dinsdale et al. (1978) using this technique. When chemically modified or microbiologically enriched cellulosic samples are to be screened for digestibility, it involves a lot of time. We report, in this communication, that an anaerobic digester, in which similar degradations of fibres to those in the rumen are occurring, can be employed to find out the percentage digestibility.

METHODS

Substrates

Cotton stalks from the variety Hybrid-4 (Gossypium hirsutum Linn.) and rice straw (Oryza sativa Linn.) cut to 3-5 cm were used for raising mushrooms, whereas powdered samples (20 mesh) were used for digestibility tests.

229 Biological Wastes 0269-7483/87/$03.50 © Elsevier Applied Science Publishers Ltd, England, 1987. Printed in Great Britain

230 R. H. Balasubramanya, S. P. Bhatawdekar, Ix. G. Khandeparkar

Pleurotus sajor-caju (Fr.) Singer was obtained from the Mushroom Research Laboratory, Himachal Pradesh Krishi Vishwa Vidyalaya, College of Agriculture, Solan, India, and maintained on Potato Dextrose Agar (PDA) slants. Grain spawn of this fungus o n wheat grains was prepared according to the method of Garcha & Kalra (1979).

The mushroom cultivation was carried out on both the substrates as described earlier (Balasubramanya, 1981). Total nitrogen was determined by a conventional micro-Kjeldahl method and the protein was N x 6"25.

In vitro rumen digestibility was determined by the modified method of Mellenberger et al. (1970). To 100-ml test tubes, 500 mg of the substrate and 35 ml of rumen fluid (diluted i:1 with artificial saliva; McDougall, 1948) were added and bubbled with biogas and immediately the tubes were corked and sealed with paraffin wax and incubated for 48 h at 39°C in an end-to-end shaker water bath. The rumen fluid was collected from a fistulated cross-bred cow maintained on green grass hay with free access to dried grass. The tube contents were centrifuged, washed once with distilled water and later dried at 105°C. The loss of weight is reported as percentage in vitro rumen digestibility.

Digestibility in anaerobic digester

The batch anaerobic digester was a 10-1itre Corning bottle with an inlet from one side, almost half way down, and an L-shaped outlet tube from the bot tom on the other side.

The digester was charged with willow-dust, a textile processing residue, with cattle waste as inoculum as per the method of Balasubramanya et al. (1981) excepting that the substrate to liquid ratio was maintained as 1:12 in order to easily suspend the nylon bags in the liquid. The digester was most active during the second and third weeks, as evidenced by the production of biogas, and needed a fresh change after every 30 days (Khandeparkar et al., 1981). Hence the experiments were conducted during the active period only. The digester was incubated without agitation at room temperature (28 + 4°C).

Powdered samples (0"5 or 1"0 g) in nylon bags (10 cm x 5 cm) of pore size 5/tm were suspended in the anerobic digester through the inlet. Each bag was tied with a long thread (non-biodegradable) to facilitate labelling and easy handling. After removing from the digester, the bags were rinsed in tap water and the contents were carefully removed and suspended in water and centrifuged, washed once with distilled water and dried at 105°C. The loss of weight is reported as percentage digestibility.

Anaerobic digestion for rumen digestibility 231

RESULTS AND DISCUSSION

It has been established that the cellulosic materials from which a mushroom crop is taken have an increased protein value, improved percentage digestibility and a characteristic odour. The flavour has a direct bearing on the acceptability of the material by ruminants. The cotton stalks and rice straws had 5"2 and 2-4mg protein per 100mg of the sample before inoculation and 8"6 and 5"2 after the mushroom growth.

The percentage digestibilities of the various cotton stalks and rice straw are given in Table 1. The tests showed that 72h incubation gave a

TABLE 1 Percentage Digestibility of Cellulosic Materials Before and After

Mushroom Growth*

Cotton stalks Rice straw

Before (a) 19.5 25.3 (b) 23'3 25.0

After (a) 25.5 30"6 (b) 30.3 32.3

(a) Anaerobic digester (after 72 h). (b) With rumen fluid (after 48 h). * Average of ten samples from five tests in duplicate.

digestibility comparable to the standard 48 h of the rumen fluid test. The continuous agitation and constant temperature of 39°C in the case of rumen fluid tests might have reduced the incubation time as compared to that in the anaerobic digester. Increased digestibility after mushroom growth is normally found. The digester system offers several advantages. A number of samples can be screened at a time and, depending upon the number of samples, the number of digesters can also be increased. It would also be possible to charge the digesters with the substrates to be tested provided the system is standardized. The cost of maintaining a system of anaerobic digesters is low. However, more tests with different substrates and different anaerobic digester conditions are required before the method can be fully recommended.

REFERENCES

Balasubramanya, R. H. (1981). An edible mushroom crop on cotton stalks. Indian Soc. Cotton bnp., 6, 104-6.

232 R. H. Balasubramanya, S. P. Bhatawdekar, V. G. Khandeparkar

Balasubramanya, R. H., Khandeparkar, V. G., Betrabet, S. M. & Sundaram, V. (1981). Production of biogas from willow-dust by a batch fermentation process. J. Text. Assn, 42, 145-9.

Dinsdale, D., Morris, E. J. & Bacon, J. S. D. (1978). Electron microscopy of the microbial populations present and their modes of attack on various cellulosic substrates undergoing digestion in the sheep rumen. AppL Environ. MicrobioL, 36, 160-8.

Garcha, H. S. & Kalra, K. L. (1979). Spawn production and its viability, Indian J. Microbiol., 19, 214-16.

Khandeparkar, V. G., Balasubramanya, R. H., Ganesan, S. & Sundaram, V. (1981). Biogas from willow-dust, Indian Cotton Mills Fed. Z, 18, 5-9.

McDougall, E. I. (1948). Studies on ruminant saliva 1. The composition and output of sheep's saliva. Biochem. J., 43, 99-108.

Mellenberger, R. W., Salter, L. D., Millett, M. A. & Baker, A. J. (1970). An in vitro technique for estimating digestibility of treated and untreated wood. J. Anita. Sci., 30, 1005-11.

Morris, E. J. (1976). A cetyl content and sugar composition as factor influencing the digestion of grass cell walls in the rumen. PhD Thesis, University of Aberdeen.

Morris, E. J. & Bacon, S. D. (1977). The fate of acetyl groups and sugar components during the digestion of grass cell walls in sheep. J. Agric. Sci., Cam&, 89, 327~.0.

R. H. Balasubramanya, S. P. Bhatawdekar & V. G. Khandeparkar Cotton Technological Research Laboratory, Post Bag No. 16640, Adenwala Road, ( I C A R ), Matunga, Bombay--400019, India

(Received 14 December 1986; revised version received 20 February 1987; accepted 13 March 1987)