SUMMARYStrains of Streptococcw bovis, Selenomonas ruminantiurn, and an anaerobic lipolytic bacterium ( 5 s) have been grown under carbohydratelimiting conditions in continuous culture for long periods. With s. ruminuntium and bacterium 5 s the fermentation products varied with growth rate. Yield of organism in continuous culture of all three bacteria showed a maximum a t a particular growth rate. The yield of S. rumimafitium was much higher in continuous culture at optimum growth rate than in batch culture, and was also higher than can be explained on present concepts of the energy from fermentation available for growth. The various results are discussed in the light of results obtained with other bacteria and the conditions obtaining in the rumen.
In previous work the rumen microbiology of young animals fed on a high carbohydrate ration has been considered and has tended to be fairly consistent (Eadie, Hobson and Mann, 1959; Eadie, 1962). In this note a further controlled experiment on calves weaned on to a 50:50 mixture of roughage/high concentrate mixture and on to the high concentrate alone, is reported. In view of interest in the intensive feeding of cattle on barley these results from young animals are compared with a series of observations made more recently on older animals fed predominantly on barley, since it was obvious from the outset that the physical nature of the rumen contents was different in the two age groups. The sudden introduction of large amounts of carbohydrate into the diet of animals previously fed conventionally has been shown to create profound changes in the rumen microbial population (Krogh, 1961) and the microbiology of the young concentrate-fed calf was very different from the roughage-fed animal. However, the barley-fed steers used in this work had been early weaned on to a high concentrate ration and had clearly become adapted to the adult high carbohydrate diet.
SUMMARYModifications to an anaerobic continuous culture apparatus to allow pH control, and pH and Eh measurements, are described. Two anaerobic rumen bacteria were grown under different conditions, but as carbohydrate-limited cultures. The effects of growth rate, pH value and Eh value on yields of bacteria, enzyme activities and fermentation products are described. Optimum bacterial yields per mole of substrate fermented and per mole of ATP presumably formed in the fermentation were variable with the particular bacterium and the substrate, and were high for hexose fermentations. Yields of bacteria varied with growth rate, being lowest at low growth rates. Fermentation products also varied with growth rate and the pH value of the culture in some cases, as did the production of enzymes. Maximum growth rates calculated from batch cultures were in agreement with those found in the continuous cultures.
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