Polysaccharide synthesis and degradation by rumen micro-organisms in vitro

I . Steers, fitted with simple rumen and duodenal cannulas, were given diets of approximately equal parts of flaked maize and hay (A) (containing 16g nitrogen/kg dry matter (DM)) or diets of flaked maize and straw supplemented with decorticated groundnut meal (B), fish meal (C), or heated (D) or unheated (E) soya-bean meal (containing 24 g N/kg DM). Chromic oxide was given as a marker with the feeds, and flows of different combined sugars at the duodenum estimated from the values for sugars: marker at this site. Contributions of bacterial constituents to these flows were estimated from amounts of RNA present.2. Rumen bacteria from steers receiving diet A contained approximately I 10 g a-dextranglucose/kg DM and contributed about 60 g a-dextran-glucose/d at the duodenum; bacteria from steers receiving diets B, C, D or E contained 25-40 g a-dextran-glucoselkg DM and contributed about 20-30 g a-dextran-glucoseld at the duodenum. There were no significant differences between different N supplements. About half the a-dextran-glucose, varying amounts of the mannose and galactose, and nearly all the rhamnose and ribose in duodenal digesta were contributed by the bacteria. Almost all the arabinose, xylose and celluloseglucose was of dietary origin.3. For steers receiving diet A, mean coefficients of digestibility between mouth and duodenum, corrected where necessary for bacterial contribution, were 0.96, 0.73, 0.58, 0.22 and 0.53 for starch-glucose, galactose, arabinose, xylose and cellulose-glucose respectively. Corresponding mean values when diets B, C, D and E were given, which did not differ significantly amongst themselves, were 0.98, 0.79, 0.81, 0.59 and 0.58. Most values for galactose, arabinose and xylose were significantly higher than the diet A values.

mentioning

confidence: 80%

mentioning

confidence: 99%

Effect of dietary nitrogen source on carbohydrate metabolism in the rumen of the young steer

McAllan¹,

Smith²

1976

“…The latter finding is more difficult to explain and may be related to reduced synthesis of polysaccharide in the absence of protozoa, more energy being used in P and N incorporation (Van Nevel & Demeyer, 1977). According to Thompson & Hobson (1971), however, bacteria may be more important than protozoa in polysaccharide synthesis. Differences in N: P of the growing micro-organisms in periods I and 3 as compared to period 2 may also be involved.…”

Section: Effect Of Defamation On Synthesis and Degradation Of Micromentioning

confidence: 99%

Effect of defaunation on the metabolism of rumen micro-organisms

Demeyer¹,

Nevel²

1979

129

1. Rumen contents of a fasted fistulated wether, obtained in a faunated, defaunated and refaunated period were incubated in vitro with a mixture of cellobiose and maltose, in the presence of ammonium bicarbonate and32PO43−. Total synthesis of microbial N (Nt) was calculated from32P incorporation and N:P determined in microbial matter. The N:P value was not affected by defaunation. Net synthesis of microbial N (Nn) was calculated from ammonia-N incorporation. An estimate of degradation of microbial N was calculated as Nt–Nn. Energetic efficiency of synthesis was calculated from the volatile fatty acids produced during incubation, as g N incorporated per kg organic matter fermented (g N/kg OMf).2. Defaunation decreased the proportions of acetate, butyrate and methane and increased those of propionate in fermentation end-products. Fermentation rate when expressed per mg microbial N was not affected by defaunation.3. Expressed per unit volume of rumen contents, Nnwas increased by defaunation whereas Nfremained unchanged. Thus, a decrease in degradation can be calculated. Energetic efficiences of total and net synthesis were increased from 35 and 13 to 47 and 30 g N/kg OMfrespectively.4. Specific rates of both total and net synthesis of microbial N were significantly increased by defaunation whereas the specific rate of degradation was not affected.

“…Although rumen microbes contribute appreciably to the nutrients entering the duodenum of the ruminant, there is little information concerning the composition of mixed rumen bacteria (or protozoa) under different feeding conditions. It has been known for many years that some rumen bacteria can, under certain conditions, accumulate intracellular polysaccharide in vitro (Doetsch, Robinson, Brown & Shaw, 1953;Gibbons, Doetsch & Shaw, 1955;Hobson & Mann, 1955;Doetsch, Howard, Mann & Oxford, 1957;Thomas, 1960;Hungate, 1963;Thompson & Hobson, 1971). The accumulation depends on the presence of a suitable source of energy in excess of that required immediately for metabolic purposes such as protein synthesis.…”

mentioning

confidence: 99%

Carbohydrate metabolism in the ruminant

McAllan¹,

Smith²

1974

I . Samples of mixed bacteria were separated from rumen digcsta taken from calves, kept out of contact with adult animals, and from sheep and cows.2. For calves receiving a diet made up of equal amounts of roughage and cereals with 13-16 g nitrogenlkg dry matter, samples of mixed bacteria taken 4-6 h after feeding contained, on average, 140 g glucose in a-linked polymers (a-dextran), 25 g galactose and a total of 25 g other non-glucose, non-galactose sugars (mainly rhamnose, ribose and mannose) in combined forms per kg dry matter. 3.The a-dextran content of similar bacteria samples from sheep or cows receiving diets of similar composition was 70 g/kg dry matter. Samples from animals receiving all-roughage diets contained only 2j g a-dextranlkg dry matter, but those from cows given more than 70')" of their ration as concentiates (mainly cereal) contained 150 g a-dextranlkg dry matter.4. Addition of supplementary protein or urea to cereal-roughage diets given to calves greatly depressed the amount of a-dextran in the rumen bacterial samples to an average value of 60 g/kg dry matter. j. Samples taken before a morning feed (i.e. after 16 h fasting) contained less a-dextran than samples taken 4-6 h after feeding for both calves and cows.6. Under different conditions, variations in the amounts of galactose in rumen bacteria sometimes paralleled variations in a-dertran. Amounts of other non-glucose sugars did not vary greatly.7. It was estimated, from a comparison of the compositions of rumen bacteria and duodenal contents, that, in the latter, the rhamnose, ribose and mannose came mainly from the bacteria, the arabinose, xylose and cellulose-glucose mainly from the diet and the galactose and a-dextran-glucose from both sources.Although rumen microbes contribute appreciably to the nutrients entering the duodenum of the ruminant, there is little information concerning the composition of mixed rumen bacteria (or protozoa) under different feeding conditions. It has been known for many years that some rumen bacteria can, under certain conditions, accumulate intracellular polysaccharide in vitro (Doetsch, Robinson, Brown & Shaw, 1953; Gibbons, Doetsch & Shaw, 1955; Hobson & Mann, 1955;Doetsch, Howard, Mann & Oxford, 1957;Thomas, 1960;Hungate, 1963; Thompson & Hobson, 1971). The accumulation depends on the presence of a suitable source of energy in excess of that required immediately for metabolic purposes such as protein synthesis. This excess energy may be supplied by a number of carbohydrates, but the small amount of available evidence suggests that the polpsaccharide which accumulates consists mainly of glucose polymers. Apart from the recent work of Jouany & Thivend (1972b), there is little information on over-all carbohydrate composition of mixed bacteria developing in the rumen or on the factors infiuencing the polysaccharide accumulation. The present work is an attempt to provide such information and to assess the relative amounts of bacterial and residual food carbohydrate entering the duodenum of the ruminant.http...