In addition to the bacteria in the rumen there are many larger (5–250/mm long) organisms which at various times have been designated protozoa Of these the ‘ovals’ (Quin’s and Eadie’s) are now known to be large bacteria (Orpin, 1976) and the ‘flagellates’ Neocallimastix frontalis, Piromonas communis and Sphaeromonas communis are the zoospores of phycomycete fungi (Orpin, 1977a, b) There are genuine flagellates in the rumen, eg Trichomonas spp, Monoceromonas sp and Chilomastix sp, but almost nothing is known about their metabolism (Jensen and Hammon, 1964) The largest, most obvious and most important protozoa are the ciliates, of which there are two groups both in the subclass Trichostomatia The so called ‘holotrich’ protozoa belong to the order Vestibuliferida and the entodiniomorphs to the order Entodiniomorphida, suborder Entodiniomorphina and family Ophryoscolecidae As the properties and metabolism of these two protozoal groups are different, they will be considered separately below

The Rumen Protozoa

Chemical factors involved in ruminal fiber digestion.

Recent advances in chromatographic identification of CLA isomers, combined with interest in their possible properties in promoting human health (e.g., cancer prevention, decreased atherosclerosis, improved immune response) and animal performance (e.g., body composition, regulation of milk fat synthesis, milk production), has renewed interest in biohydrogenation and its regulation in the rumen. Conventional pathways of biohydrogenation traditionally ignored minor fatty acid intermediates, which led to the persistence of oversimplified pathways over the decades. Recent work is now being directed toward accounting for all possible trans-18:1 and CLA products formed, including the discovery of novel bioactive intermediates. Modern microbial genetics and molecular phylogenetic techniques for identifying and classifying microorganisms by their small-subunit rRNA gene sequences have advanced knowledge of the role and contribution of specific microbial species in the process of biohydrogenation. With new insights into the pathways of biohydrogenation now available, several attempts have been made at modeling the pathway to predict ruminal flows of unsaturated fatty acids and biohydrogenation intermediates across a range of ruminal conditions. After a brief historical account of major past accomplishments documenting biohydrogenation, this review summarizes recent advances in 4 major areas of biohydrogenation: the microorganisms involved, identification of intermediates, the biochemistry of key enzymes, and the development and testing of mathematical models to predict biohydrogenation outcomes.

http://webpages.icav.up.pt/PTDC/CVT/122245/2010/02.pdf

Board-invited review: Recent advances in biohydrogenation of unsaturated fatty acids within the rumen microbial ecosystem.

The effect of starch on forage fiber digestion kinetics in vitro.

Influence of hydrogen on rumen methane formation and fermentation balances through microbial growth kinetics and fermentation thermodynamics

A survey of the components of the rumen ciliate population in a series of adult sheep, raised in the Faculty of Agriculture, University of Alexandria, has shown that a mixture of Entodinium, Isotricha, Ophryoscolex, Diplodinium, and Polyplastron species was found in the rumen contents of Egyptian sheep; no Epidinium and a negligible number of Dasytricha ruminantium were also observed. The microbial population, reducing sugars, ammonia, volatile fatty acids (VFA) production, and growth rate of 14 lambs inoculated with whole rumen contents from a mature sheep were compared over a 6-month period with those of 13 lambs maintained under the same conditions, except that they were strictly isolated from other ruminants. Certain large oval organisms and large numbers of flagellates and Oscillospira were frequently observed in the rumen contents of the isolated lambs. The reducing sugars, ammonia, and VFA levels, measured before and at intervals after feeding, in the inoculated lambs showed a pronounced rise above the values found in the ciliate-free animals. The propionic acid-acetic acid ratio in the rumen contents of the faunated lambs was considerably higher than in the nonfaunated controls. The inoculated lambs grew faster than the isolated lambs. Differences in weight gain which ranged from 15 to 17% were statistically significant. The inoculated animals impressed the observers by their good appearance which was superior to that of the ciliate-free lambs. It was, therefore, concluded that the rumen ciliate protozoa are essential for the metabolism and growth of young lambs.

https://aem.asm.org/content/aem/12/4/384.full.pdf

Effect of absence of ciliate protozoa from the rumen on microbial activity and growth of lambs.

1. The levels of blood reducing sugars, haemoglobin, protein N, NPN, ammonia N, and urea N in addition to the nitrogen retention and digestibility coefficients of food constituents, were studied in lambs with and without ciliate protozoa. 2. The inoculated lambs have higher blood haemoglobin, protein N, and lower reducing sugars, ammonia N, and urea N values than those of the uninoculated lambs.

Effect of presence or absence of rumen ciliate protozoa on some blood components, nitrogen retention, and digestibility of food constituents in lambs.

Effect of early establishment of ciliate protozoa in the rumen on microbial activity and growth of early weaned buffalo calves.

Establishment of Rumen Ciliate Protozoa in Cow and Water Buffalo (Bos bubalus L.) Calves Under Late and Early Weaning Systems

Washed suspensions of mixed rumen protozoa readily hydrogenated fatty acids in cottonseed, soya bean and corn oils in addition to free oleic and linoleic acids. Protozoa belonging to the family Ophryoscolecidae appeared to account for almost all the activity of mixed protozoa, protozoa of the family Isotrichidae possessing little or no ability to hydrogenate the added substrates. The hydrogenation of oleic acid was markedly increased by Fe and Mn. The addition of starch cellulose, urea and sodium formate greatly stimulated hydrogenation of oleic acid by rumen protozoa. Glucose, casein, ammonium sulphate, L-cysteine and n-valeric acid had no or little effect on extent of hydrogenation.When suspensions of mixed protozoa were incubated in a buffer solution, an increase in iodine value was observed. The desaturation in the protozoal cells was appreciably increased by DL-methionine and was not influenced by L-cysteine. No desaturation activity by the pure suspensions of Ophryoscolecidae or Isotrichidae was observed.The presence of protozoa in the rumen of sheep greatly increased the levels of saturated fatty acids over those in the ciliate-free animals. The concentrations of saturated fatty acids in the plasma of faunated sheep were significantly higher than those in the same animals after the removal of rumen ciliate protozoa.

A. R. Abou Akkada

Papers

Effect of absence of ciliate protozoa from the rumen on microbial activity and growth of lambs.

Effect of presence or absence of rumen ciliate protozoa on some blood components, nitrogen retention, and digestibility of food constituents in lambs.

Effect of early establishment of ciliate protozoa in the rumen on microbial activity and growth of early weaned buffalo calves.

Establishment of Rumen Ciliate Protozoa in Cow and Water Buffalo (Bos bubalus L.) Calves Under Late and Early Weaning Systems

Effect of rumen protozoa on dietary lipid in sheep