Ruminant Nitrogen Usage (1985) / Chapter Skim
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6 Microbial Growth
6 Microbial Growth
Pages 37-45
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From page 37... ...
Few bacterial species have proteolytic capability, and a few species are responsible for most of the digestion of cellulose. As a result, the composition of the diet can alter the rumen ecology and influence microbial growth, total microbial mass, and extent of dry matter digestion.
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From page 38... ...
Nutrient requirements could be expressed in terms of rate of microbial growth and microbial type. It is difficult to consider bacterial type because of the range in maintenance requirement and variation in nutrient requirements.
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From page 39... ...
Amino acids and branched chain volatile fatty acids are required by cellulolytic bacteria in vitro, but crossfeeding can meet this need in the rumen under most circumstances (Hume, 1970; Stewart, 1975; Chalupa, 1976, Russell et al., 1979~. The amount of ammonia required for microbial growth has been researched, modeled, and reviewed extensively (Nolan et al., 1972; Thomas, 1973; Satter and Roffler, 1975, Smith, 1975, 1979; Mehrez et al., 1977; Baldwin and Denham, 1979; Kennedy and Milligan, 1980; Schaefer et al., 1980; Beever et al., 1980, 1981; Black et al., 1980-1981; Kang-Meznarich and Broderick, 1981~.
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From page 40... ...
MICROBIAL GROWTH AND FLOW Microbial growth will be discussed in three contexts: microbial efficiency, microbial mass, and microbial flow. Efficiency and mass are dependent on the specific substrate available for fermentation in the rumen, pattern, composition and rate of substrate availability, and environmental factors.
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From page 41... ...
Dry matter intake will influence not only the quantity and possibly the type of substrate available for synthesis of microbial protein, but also various ruminal parameters such as pH and dilution rate and microbial determinants such as bacterial dilution rate, protozoa! presence and bacterial numbers, distribution, and lysis in the rumen.
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From page 42... ...
42 Ruminant Nitrogen Usage TABLE 8 Recressions for Dairy Cattle~ Sheep' and Beef Cattle Model Regressions R~ S.E.
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From page 43... ...
adjusted the estimates of ruminally fermented organic matter for microbial mass, thus giving an estimate of truly fermented organic matter, and calculated percentage of total tract digestion occurring in the rumen. For cattle trials for which total tract digestibilities were available, percent of total tract digestion occurring in the rumen was 76 + 10.
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From page 45... ...
Further research is needed to develop quantitative dynamic prediction models that will incorporate measurements of diet type and processing johnson and Bergen, 1982) , rumen escape estimates, and potential substrate degradability on various microbial niches in the rumen and flow of microbes from the rumen.
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