Distribution of bacteria in the rumen contents of dairy cows given a diet supplemented with soya-bean oil

Abstract

1. Liquid-associated bacteria (LAB) were harvested from the liquid phase (LABI) and from the solid phase of rumen contents after washing and manual shaking (LAB2). Solid-adherent bacteria (SAB) were recovered after washing and pummelling the total particles (SAB I). The distribution and the chemical composition of these three bacterial compartments were investigated in four dairy cows fitted with rumen fistulas. The animals received successively a diet consisting of one part hay and one part barley-based concentrate (diet C) and the same diet containing free soya-bean oil (79 g/kg dry matter (DM); diet So).2. The efficiency of removal of SABl from total particles of rumen digesta collected 1 h after feeding, was calculated from the diaminopimelic acid content in particles and of the corresponding detached bacteria. It was 24% on diet C and 18 YO on diet So ( P < 005), using a combination of homogenizing and 'stomaching' treatments in saline (9 g sodium chloride/ 1) (reference treatment). For diets C and So respectively it was lowered by Tween in saline solution (1 g/l ; 22.7 and 17.8 %, not significant), but was increased when using a previous chilling (6 h at 4") of homogenized particles before stomaching in saline (28.8 and 24.7Y0, P < 0.05) and in Tween 80 in saline (1 g / l ; 26.6 and 208%, P < 0.05).3. The extent of removal of SABl from the solid fraction of rumen digesta by the reference treatment decreased with decreasing particle size; it was at the highest for particles retained on 4 and 2 mm sieves (62.1-82.1 %) and still elevated for particles retained on 08, 0.4 and 0.1 mm sieves (41.3-579%). It was very much reduced for particles smaller than 0.1 mm (1 1.7-14.5 X), suggesting the occurrence of favourable conditions for the adhesion of SAB firmly resistant to removal (SAB2).4. The concentration of total SAB (SAB1 + SAB2) in particles collected 1 h after feeding was lower ( P < 0.05) in diet C (190 g/kg DM) than in diet So (234 g/kg DM). Values averaged 595445 g/kg DM for particles smaller than 0.1 mm, but only 61 and 81-98 g/kg DM for particles retained on 4 and 0.4 mm sieves, and on a 0.1 mm sieve respectively. No significant differences were noted hetween diets but the effect of particle size was highly significant ( < 0 1 mm v. others).5. Postprandial variations of concentrations of total SAR on total particles exhibited a large increase I h after feeding in diet So ( P < 0.05). Similar but amplified variations were observed for LAB in both diets ( P < 0.05).6. Total bacterial mass amounted to 213 and 231 g DM/kg whole-rumen contents DM in diets C and So respectively 6 h after feeding. Mean percentages of total SAB (69.8), LAB1 (7.3) and LAB2 (22.9) in total rumen contents were not significantly modified by the lipid level of the diet.

Role of the protozoan Isotricha prostoma, liquid-, and solid-associated bacteria in rumen biohydrogenation of linoleic acid

“…Hence, SAB were not obtained from bulk, coarser solids retained by a wire gauze (1 mm mesh) as in other studies, e.g. Legay-Carmier and Bauchart (1989). It should be also noted that LAB and SAB fractions obtained in the current study could be atypical since the source of microorganisms was a single wether monofaunated with I. prostoma.…”

“…The latter two incubations starting with biohydrogenation intermediates were performed since I. prostoma and/or its associated bacteria are possibly involved in only part of the rumen biohydrogenation of C18:2n-6. Experiment 2: Role of LAB and SAB in rumen biohydrogenation LAB and SAB were obtained following a centrifugation procedure of Legay-Carmier and Bauchart (1989) with some modifications. Briefly, 2 3 200 ml of I. prostoma monofaunated rumen fluid was centrifuged during 3 min at 500 3 g. From one aliquot, the supernatant was collected by suction and diluted with autoclaved I. prostoma monofaunated rumen fluid to the initial volume of 200 ml.…”

Digestion of fatty acids in ruminants: a meta-analysis of flows and variation factors. 1. Total fatty acids

“…First, the values for total FA content in bacteria do not distinguish FA from bacterial synthesis and FA of dietary origin that are adsorbed on the cell wall or included in the cytoplasm. Second, it is well known that there are important differences in metabolic activities and FA composition between LAB and SAB (Bauchart et al, 1990), whose relative proportions in the ruminal samples depend on the sampling procedure used to harvest these two fractions (Legay-Carmier and Bauchart, 1989). Moreover, it remains to establish whether the separation procedures isolated protozoa from bacteria, because protozoa may also contribute to the duodenal flow of microbial FA.…”

Reassessing the manipulation of protein synthesis by rumen microbes

“…LAB account only for 15-30 p100 of the microbial OM in the rumen (Craig et al, 1987;Olubobokun ef al, 1988;Legay-Carmier and Bauchart, 1989 (1989) calculated that the extraction rate decreased with decreasing particle size.…”