Introduction Cellulolytic bacteria, such as Ruminococcus albus, R. flavefaciens and Fibrobacter succinogenes are major micro-organisms responsible for ruminal digestion of plant cell walls ingested by the animal due to their numerical predominance and metabolic diversity (Cheng et al., 1991). It has been proposed that sodium hydroxide might breakdown hemicelluloses, expose the cellulose to microbial attachment and improve digestibility (Chen et al., 2006). The objective of this experiment was to estimate the disappearance of dry matter (DM) and neutral detergent fibre (NDF) of sunflower meal (25 g fat/kg DM; SM) as untreated or treated with formaldehyde (3 g/kg DM) or sodium hydroxide (40 g/kg DM) using in vitro culture with isolated mixed rumen bacteria. Materials and methods Rumen fluid was collected from four fistulated sheep which fed 250 g concentrate, 550 g lucerne hay and 200 g wheat straw, then centrifuged (1000 RPM, 10 min). Supernatant was used to grow bacteria in bacteria medium containing fungicides (benomyle: 500 ppm/ml of medium and metalaxyle: 10 mg/ml of medium) under anaerobic conditions at 39 ºC for 24 h. These isolates were then used as a source of inoculum for culturing bacteria in a serum bottle containing 45 ml of culture medium of bacteria (Galdwell and Bryant, 1966) and 1g of sunflower meal as untreated or treated with formaldehyde (3 g/kg DM) or sodium hydroxide (40 g/kg DM) under anaerobic conditions (using three times subculture), at 39 ºC in an incubator for 12, 24, 48, 72 and 96 h. Three replicates were run per treatment per time. The residual substrates of each bottle were then filtered and used to determine the DM and NDF concentrations. Data of DM and NDF disappearance in different times were analysed as a completely randomized design using the General Linear Model (GLM) procedure of SAS (1990). Duncan’s multiple range test was used to compare the means at P< 0.05. Results Disappearance of DM and NDF of samples using isolated mixed rumen bacteria culture are given in Table 1. Disappearance rate of DM and NDF of sodium hydroxide treated samples was markedly higher than the other samples, in each incubation time. Formaldehyde caused to decrease the disappearance of DM and NDF of sunflower meal using rumen mixed bacterial in vitro culture. Table 1 Dry matter (DM) and neutral detergent fibre (NDF) disappearance of sodium hydroxide or formaldehyde treated sunflower meal using isolated rumen bacteria in vitro culture IT (h) DM disappearance (g /100g) NDF disappearance (g/100 g) USM SHSM FSM s.e.m P USM SHSM FSM s.e.m P 12 36.3b 42.0a 31.2c 0.77 < 0.01 10.1b 14.5a 8.3c 0.51 < 0.01 24 42.6b 47.1a 33.4c 0.65 < 0.01 19.5b 21.3a 15.9c 0.72 < 0.01 48 51.1b 58.2a 44.2c 0.79 < 0.01 26.5b 29.6a 23.3c 0.80 < 0.01 72 59.2b 67.1a 54.1c 0.87 < 0.01 28.2b 31.0a 24.4c 0.84 < 0.01 96 57.3b 62.3a 56.3b 0.62 < 0.01 27.7b 30.6a 23.7b 0.72 < 0.01 IT: incubation time; USM: untreated sunflower meal (SM); SHSM: 40 g NaOH /kg DM of SM; FSM: 3 g formaldehyde /kg DM of SM; s.e.m: standard error of mean; abc: means with different letters within each row differed significantly. Conclusions In vitro bacterial digestion of feed samples used in the present experiment was influenced by chemical compounds of NaOH or formaldehyde. Sodium hydroxide caused to increase the bacteria digestion of DM and NDF, while formaldehyde decreased the digestion using in vitro culture. Results of the present study confirmed previous results which used an alkaline solution to increase the disappearance rate of DM and NDF. Gould (1984) reported that the dilute solutions of alkaline react with lignocelluloses to yield partially de-lignified products that are highly susceptible to enzymatic and microbial attack. Bas et al. (1989) reported that the DM and NDF digestion of straw treated with an alkali was greater than untreated straw. Results of the present study indicated that the potential improvement in DM and NDF digestion of sunflower meal could be resulted from the use of sodium hydroxide. References Cheng, K. J., Forsberg, C. W., Minato, H. And Costerton, J. W. 1991. In: Physiological Aspects of Digestion and Metabolism in Ruminants (Tsuda, T., Sasaki, Y. and Kawashima, R., eds.), pp. 595-624. Academic Press, Toronto, ON Chen, X.L., Wang, J.K., Wu, Y.M., and Liu, J.X. 2007. Animal Feed Science and Technology. 141, 1-14. Caldwell, D.R. and Bryant, M. P. 1966. Applied Microbiology. 14, 794–801. Bas, F. J., Stern, M. D. and Fahey, G. C. 1989. Journal of Animal Science. 67, 2081-2088 B Gould, J. M. 1984. Biotechnology and Bioenergetic. 26, 46-52.

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