Determination of rumen microbial growth in vitro from³²P-labelled phosphate incorporation

Abstract

1. The extracellular phosphate pool in incubations of rumen fluid or washed cell suspensions of mixed rumen bacteria (WCS) was labelled with 32P. From the constant extracellular phosphate pool specific activity and the amount of radioactivity incorporated during incubation, the amount of P incorporated in the microbial fraction was calculated. From the value for nitrogen: P determined in microbial matter, the amount of N incorporated was calculated as a measure of microbial growth. 2. Incorporation of soluble non-protein-N in incubations devoid of substrate protein was 50 and 80% of the values obtained using the isotope method for rumen fluid and WCS respectively. It is suggested that results obtained using the former method reflect 'net growth' of micro-organisms which is the result of simultaneous growth and degradation. The isotope method measures 'total growth', as isotope incorporation is not affected by degradation of non-growing cells. 3. Incorporation of 32P in P-containing microbial components (mainly nucleic acids) was compared with net synthesis of these components in incubations of WCS. The results showed different specific rates of synthesis and degradation for all components studied. It is concluded that the composition of microbial matter changed during growth. 4. When N incorporation, calculated from results obtained using the isotope method in incubations with rumen fluid, was compared with the amount of carbohydrate substrate fermented and the type of fermentation, values between 18-3 and 44-6 g N incorporated/kg of organic matter fermented were obtained. Low values were associated with large proportions of the substrate being fermented to lactate and the use of glucose instead of disaccharides as substrate. Part of the variation could also be attributed to differences in incubation period, reflected in different proportions of polysaccharide formed. 5. The use of isotopes for determination of rumen microbial growth in vitro is critically discussed.

Influence of substrate and microbial interaction on efficiency of rumen microbial growth

“…Such predation is probably not accounted for by Pirt-like maintenance equations (Hobson and Wallace, 1982) as it necessitates the adaptation of mathematical models for continuous culture (Smouse, 1981). The detrimental role of protozoa in rumen microbial N yield was speculated upon in earlier work (review in Demeyer, 1981) and demonstrated by the determination of simultaneous total synthesis and degradation of microbial matter in vitro (Van Nevel and Demeyer, 1977) using faunated and defaunated mixed rumen microorganisms . The absence of protozoa lowered degradation and slightly increased total synthesis, resulting in a considerable increase of net synthesis (e.g.…”

“…Demeyer, 1977) (Cummins et al, 1983) around a mean of about 30, a figure introduced in systems for ruminant feed protein evaluation (Jarrige et al, 1978 ;Roy et al, 1977). Although experimental error is an important factor in variability (Faichney, 1975 ;Sutton, 1979 ;Ling and Buttery, 1978), recent data have permitted the conclusion that, provided rumen degradable protein is not a limiting factor of microbial growth, diets largely based on concentrates and on silage give lower E values than mixed diets (Tamminga, 1983) or forage diets Van Soest, 1982).…”

“…Fermentation rate, irrespective of fermentation pattern, reflects growth rate and its increase augments E ( fig. 2) (Demeyer and Van Nevel, 1975a), unless the need to dispose rapidly of ATP increases lactate production, decreasing SLP and, thus, E (Van Nevel and Demeyer, 1977). Concomittant increases in polysaccharide synthesis and decreases in pH may also lower E. Microbial growth is very sensitive to changes in pH (Hoover et al, 1984), possibly because of interference with the generation of proton motive force, a low pH reducing ETP (Erfle et al, 1984 .…”

The Effect of Urea Molasses Multi-Nutrient and Medicated Block for Beef Cattle, Beef and Dairy Cow

“…The best formula selected was obtained by using P-32 tracer to determine microbial protein synthesis in the rumen liquid [3,4].…”

Colonic fermentation of an indigestible carbohydrate (Polydextrose®): interest and limits of a faecal batch incubation system

“…The gas production was measured every h. The pH of the medium, production of short-chain fatty acids (SCFA) and hydrogen (H 2 ) and the amount of residual substrate were estimated 2, 4, 6 h after the start of the incubation. Theoretical fermented organic matter (TFOM) was calculated from total SCFA production according to Van Nevel and Demeyer (1977).…”