Estimation of the sulfur requirements of rumen microbes in a semi-continuous fermentor (Rusitec).

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 19 ESTIMATION OF THE SULFUR REQUIREMENTS OF RUMEN MICROBES IN A SEMI-CONTINUOUS FERMENTOR (RUSITEC) S. KOMSARCZUK-BONY, S. TOILLON, C. HUC and M. CARCELLEN. Ecole Nationale V&&inaire, B.P.83, 69280 Marcy l' Etoile, France. As discussed in Durand and Komisarczuk 1988, the supply of sulfur (S) to rumen microbes should be balanced with the amount of energy available for fermentation (OMF) in order to optimize microbial protein synthesis and carbohydrates degradation. The aim of the present study was to look at the effect of an increasing supply of 100% available S on the fermentation of a S-free purified substrate, using a semi-continuous fermentor, in order to determine the S microbial requirements for optimizing different parameters of the microbial activity in the rumen. The Rusitec system was run as described by Czerkawski and Breckenridge (1977). Rumen content donors sheep were fed hay and barley. Daily, 13 g of pure cellulose (Whatman paper) and 3 g of soluble starch were used as solid substrates. Urea nitrogen (220 mg N/day) and sodium sulfate (4, 8, 12 and 22 mg S/day in vessels A, B, C and D respectively) were perfused continually with an artificial saliva supplemented with trace elements, vitamins and branched-chain amino-acids. Microbial nitrogen was estimated as total non-ammonia N. Sulfides were estimated using a specific electrode (Tacussel, XS260) and sulfates according to Sorb0 (1987). No sulfate sulfur was recovered from the liquid effluents whatever the S supply was. The sulfide concentrations were 0.008,0.05,0.1 and 2.5 mg/L in vessels A, B, C and D respectively. The amount of sulfide found in the fermentation gas was negligible for vessels A, B and C but 3.6 mg/day were produced with the highest S dose tested. Therefore, in vessel D, unlike in the 3 other vessels, the efficiency of the microbial S incorporation is not total. A significant stimulation of the overall fermentation parameters (gas and short-chain fatty acids (SCFA) production, cellulose degradation and microbial N incorporation) (Table 1) was obtained when increasing the sulfur dose up to 12 mg/day (N&=20). No more response in term of activity parameters was obtained with the distribution of 22 mg S/day (N/S=ll). However, at the higher S level, total microbial N incorporation was reduced by 10% compared to the 12 mg/day supply, inducing a clear-cut reduction of the microbial N yield: 25.5 v. 28.1 g N/kg OMF in vessels C and D respectively. According to these results it can be considered that the optimal S supply to maximize the rumen microbial activity with a purified diet is 2.1 g available S/kg OMF. Table 1. Influence of the sulfur supply on different parameters of the microbial activity using a purified substrate in a Rusitec system SCFA, short chain fatty acid production; OMF, energy available for fermentation Rumen microbes seem able to adapt partially to S deficiency as the S content in washed liquidassociated bacteria decreases when the S supply decreases: 0.47, 0.50, 0.59, 0.63% OM in bacteria isolated from vessels A, B, C and D respectively. A shift in the equilibrium of the microbial species within treatment is unlikely as no significant change in the SCFA pattern was obtained when modifying the S supply. DURAND, M., KOMISARCZUK, S. (1988). J. Nutr: 118: 24940. CZERKAWSKI, J. W., BRECKENRIDGE, G. (1977). 23~ J. Nutr. 42: 217-28. S&BO, B. (1987). In ` Methods in Enzymology.' Vol. 143. (Eds W. B. Jakoby and 0. W. Griffith.) pp. 3-6. (Academic Press: London).