The Digestion of Rumen Microorganisms by the Host Animals

Complete utilization of the nutrients synthesized in the rumen by the microflora and microfauna presupposes the later disintegration of the microorganisms in order that the products incorporated in their cells may be absorbed by the host animal.The concept that the rumen microorganisms are digested by the host animals after passage from the forestomachs is quite generally accepted (3).Hastings (9) states that ruminants live to a large extent on protozoa and bacteria which are constantly carried to the true stomach, killed and digested.On the other hand, McNaught and Smith (13) cite KShler (12) as being of the opinion, based on comparative direct bacterial counts between rumen and intestinal contents, that very little protein in bacterial form is available to cattle.One of the principal details which support the supposition that rumen bacteria are later digested by the host animal is that ruminants can utilize non-protein nitrogen such as urea (4, 8, 13, 14 and 19).McNaught and Smith (13) consider that it would be almost impossible to explain this ability that ruminants possess for utilizing non-protein nitrogen as compared to other livestock such as pigs, rats and poultry, unless the conversion is accomplished by rumen microorganisms which later release their products to the host.Johnson et al. (11) mentioned the possibility that the bacteria utilize products like urea, that the bacteria are later digested by protozoa and these, in turn, are digested by the host animal.Ciliates apparently are destroyed during their passage through the digestive tract as they disappear in the abomasum (1,2,6,18).Baker (2) also has shown that they are digested by peptic and tryptic extracts.According to Mangold, as cited by Johnson et al. (11), ruminants obtain much protein through their digestion of the infusoria which pass along from the rumen.However, the presence of protozoa apparently is not essential to ruminants (5), even for the utilization of urea (11).Hastings (9) interprets this to indicate that bacterial protein is as available to the host as that from protozoa.However, the protein derived from bacterial protein may be somewhat less easily digested by the host than that from protozoa (11, 13).Baker (2) observed that iodophile bacteria of the rumen, although not affected by gastric secretions, are inconspicuous and present only in limited numbers in the caecum and feces of cattle and sheep and that partially digested microorganisms frequently are seen in caecal contents.The breakdown and disappearance, by the time the materials reached the caecum, of the strongly iodo-: