Effects of feeding frequency and level of feed intake on chemical composition of rumen bacteria

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Abstract
Cell mass (dry matter per cell) and cell composition (concentrations of DNA, RNA, phospholipids, total N, a-dextran, diaminopimelic acid and 18 common amino acids) of rumen bacteria were measured at various times after feeding sheep chaffed lucerne hay (Medicago sativa L.) once daily. Cell composition was measured with sheep fed once hourly. Total DNA and RNA pool sizes in the rumen were also measured.While cell composition was not affected by level of feed intake (700 g v. 1050 g dry matter/day), total DNA, RNA and D.M. pool sizes in the rumen increased with increasing feed intake. With sheep on the once daily feeding regimen relative rumen pool sizes in rumen digesta at various times after feeding were: RNA, 4 > 14 > 0 h; DNA, 4 and 14 > 0 h; D.M. 4 > 14 > 0 h. With the hourly feeding regimen pool sizes were similar to the averaged daily values for sheep fed once daily.When sheep were fed once daily bacterial cell mass, DNA and phospholipid concentrations peaked at 12–14 h after feeding and subsequently decreased to the 0 h value. RNA concentration was maximal at about 4 h after feeding and declined to near the 0 h value at about 14 h. RNA concentrations in bacteria were highly correlated with gas production rates by whole rumen digesta. The ratio RNA:DNA was highest shortly after feeding, decreased to below the 0 h value at about 14 h and then increased to the 0 h value. The relative concentrations of a-dextran in bacteria were: 4 > 14 > 0 h. Cell composition witli sheep fed hourly tended to reflect the averaged daily values for sheep fed once daily.These results are discussed with regard to changes in estimated fermentation rate and pool size of bacteria in the rumen. It is suggested that changes in average composition (DNA, RNA, total N and RNA: DNA ratio) of mixed rumen bacteria reflect changes in the average growth rate of the population.