Microbial protein synthesis in cattle given roughage–concentrate and all-concentrate diets: the use of 2,6-diaminopimelic acid, 2-aminoethylphosphonic acid and ³⁵S as markers

Abstract

1. Three steers, each fitted with a rumen cannula and a re-entrant cannula in the proximal duodenum, were offered diets consisting of a barley-based concentrate and chopped hay at a daily intake of 61 g/kg live ~e i g h t o '~ given in three. equal meals. The ratio, concentrate: hay was changed from 50 : 50 to 90 : 10 and then to 100 :O in successive periods of 12-18 weeks and the flow and composition of digesta at the duodenum was measured over 48-h periods on each dietary treatment. 2.Samples of bacteria and protozoa were separated from rumen contents and the proportions of bacterial and protozoal nitrogen (N) in duodenal digesta were estimated using 2,ddiaminopimelic acid (DAPA) and 2-aminoethylphosphonic acid (AEP) as markers. On separate occasions, radioactive sulphur (%) was infused into the rumen for 48 h and digesta collected over the final 24 h; the specific radioactivity of S in microbial and digesta fractions was used to estimate the proportions of microbial N.gave reproducible and apparently reliable estimates of microbial protein formation: the proportion of microbial N in digesta was significantly higher (P < 0.05) for the 50:50 diet than for the other treatments but the energetic efficiency of microbial protein formation did not differ significantly between diets. 4. Estimates of bacterial N based on DAPA concentrations were highly variable and frequently impossibly high. It is suggested that many of the anomalous values were the result of non-representative sampling of the rumen microbial population and that this is particularly likely to occur when conditions within the rumen are unstable. AEP was found to be unsuitable as a marker for rumen protozoa as considerable concentrations of this substance were found also in rumen bacteria. 3.

Estimation of microbial protein supply in ruminant animals based on renal and mammary purine metabolite excretion. A review

“…However, none of the current marker techniques satisfy all of these criteria because the ratio of markenN concentra-tions are markedly different between rumen bacteria and protozoa, and in the case of internal markers also between fluid and particulate associated bacteria (Broderick and Merchen, 1992). Furthermore, additional concerns exist with the use of DAPA Rahnema and Theurer, 1986), AEPA (Ling and Buttery, 1978;Whitelaw et al, 1984;Horigane and Horiguchi, 1990) and nucleic acids (NA) (Smith et al, 1978;Ling and Buttery, 1978;McAllan, 1982) due to their presence in feedstuffs.…”

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

“…Grinding the roughage impairs sequestration, lowers protozoal count and also promotes retention by reducing salivation and k i . The large protozoal populations associated with silage diets (Chamberlain and Thomas, 1980) (Ling et al, 1983 ;Whitelaw et al, 1984). Higher feeding levels and/or grinding concentrate diets lowers protozoal count through acidification and increased tonicity associated with intensive fermentation, reduced salivation and lower k, values, although other factors may be involved (Lyle et al, 1981).…”

A proposed simple method for determining the outflow of ciliates from the reticulo-rumen

“…The protozoa are selectively retained in the rumen (Michalowski et al, 1986) but part of their population passes down from the reticulo-rumen to the omasum and then to the abomasum and duodenum. The outflow of protozoa from the rumen has been measured indirectly, i.e as flow of protozoal protein at the duodenum (Harrison et al, 1979;Steinhour et al, 1982;Whitelaw et al, 1984;Cockburn and Williams, 1984;John and Ulyatt, 1984;Meyer et al, 1986) and by a more direct method, i.e. by counting ciliates in omasal liquid taken from omasum (Weller and Pilgrim, 1974;Punia and Leibholz, 1994) or in omasal effluent (Michalowski et al, 1986).…”