In their comprehensive review of rumen metabolism, Annison and Lewis (1959) emphasised the symbiotic relationship between the metabolic activities of the mixed population of anaerobic bacteria and ciliated protozoa, and the digestion of fodder consumed by the host. Prominent features of the microbial activity characterising the ruminant mode of
digestion have been listed by Moir (1965) and may be summarised
(1) Cellulose is hydrolysed to monosaccharides by microbial cellulases and carbohydrates fermented to volatile fatty aci s. While problems in the quantitative assessment of this volatile fatty acid production were reviewed by Warner (1964), it was also suggested that the amount produced in the rumen and
absorbed directly into the blood stream, was sufficient to meet about 70 % of the host's energy requirements.
(2) Microbial protein is synthesised from both plant protein and inorganic nitrogen with the energy released during carbohydrate fermentation. Although the extent of this
conversion has also proved difficult to quantitate, Phillipson (1964) has stated that the microbial synthesis of essential amino acids, not always present in the diet, makes the ruminant almost independent of the quality of dietary protein. [From Introduction]