Washed bacterial suspensions obtained from the pig hindgut were incubated under 13CO2 in a buffer containing NaH13CO3 and carbohydrates. Incorporation of 13C into short chain fatty acids was assayed by quantitative nuclear magnetic resonance. The effects of different levels of H2 added to the gas phase (0, 20 and 80% v/v) and of the specific methanogenesis inhibitor 2-bromoethane-sulphonic acid (BES) were determined. In control incubations increasing the concentration of H2 markedly increased methane production. Single- and double-labelled acetate and butyrate were formed in all incubations. In the absence of BES, increasing H2 significantly increased the incorporation of 13CO2 into butyrate and the proportion of double-labelled acetate in total labelled acetate. The addition of BES proved to be very successful as a methane inhibitor and greatly enhanced the amount of mono- and double-labelled acetate, especially at the highest H2 partial pressure. The results suggest that methanogenesis inhibited both routes of reductive acetogenesis, i.e. the homoacetate fermentation of hexose (represented for the most part by single labelling) and the synthesis of acetate from external CO2 and H2 (represented mostly by double labelling). A highly significant interaction between BES and H2 concentration was observed. At the highest pH2 BES increased the proportion of labelled acetate in total acetate from 17.1% for the control to 50.9%. It was concluded that although acetogenesis and methanogenesis can occur simultaneously in the pig hindgut, reductive acetogenesis may become a significant pathway of acetate formation in the absence of methanogenesis.

Summary. This paper reports the effects of a marginal phosphorus deficiency associated or not with an excess of calcium in 5 lots of 4 growing sheep each fed a semi-purified diet containing cellulose (25-27 %) and urea as the only nitrogen source.In experiment 1, two P-deficient diets (1.2 g/kg DM) poor (LPLCa) or rich (LPHCa) in Ca led to lower phosphatemia, decreased appetite and a negative or zero P balance. The effects of P deficiency were amplified by excess Ca.In experiment 2, two diets containing 1.5 g of P/kg DM and poor (LPLCa) or rich (LPHCa) in Ca were compared to a control diet (NPNCa). The two low-P diets did not produce any evident signs of deficiency and thus permitted minimal endogenous fecal loss of P to be evaluated at 24 mg/kg of live weight/day. This result confirms the figure adopted by INRA (1978) as the minimal maintenance requirement for P in sheep.Introduction.

The fermentation of [1-13C] glucose and [3-13C]lactate by bacteria isolated from sheep rumen and pig large intestine was compared by the nuclear magnetic resonance (NMR) technique. Washed cell suspensions were incubated directly in the NMR spectrometer and spectra were recorded every 10 min after injection of the labelled substrates. The results showed large differences in the fermentation patterns between rumen and hindgut bacteria. The latter pattern indicated a greater ability for formation and fermentation of lactate than that of the rumen. Moreover, with both substrates the amount of propionate formed via the acrylate pathway was always greater with hindgut than with rumen bacteria, 50% and 20% of the total, respectively.

Summary. The rumen simulation technique (Rusitec) has been used to study the effects of phosphorus (P) deficiency on bacterial protein synthesis and chemical composition and on adenosine triphosphate (ATP) concentrations in the solid and liquid phases of fermentors. 16 g DM of a P-deficient mixed diet was put into each vessel daily and the vessels were infused with about 1 1 of a P-deficient (0 mg of P) or P-supplemented (120 mg of P/1) buffer. Two vessels per treatment were used, and during a second experimental period the deficient and supplemented buffers were interchanged to determine the effects of P repletion and depletion.The proportion of bacterial N directly incorporated from dietary amino acids or peptides was greater in solid-associated bacteria (SAB) than in liquid-associated bacteria (LAB) (46 vs 19 %). P deficiency increased this proportion in both bacterial populations. Protein synthesis associated with the solid phase represented about 30 % of the total protein synthesis in the system. P deficiency induced a marked decrease in microbial protein synthesis in both phases. Microbial yield declined by about 5 points (g of N/kg OMF) in P-deficient conditions. ATP concentrations were greatly reduced in both phases but P deficiency had no effect on protozoal numbers.The effects of P depletion during period II were similar to those of P deficiency in period I, and P repletion showed that the effects of P deficiency were almost entirely reversible.Introduction.

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