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

SOME weeks ago Sir Oliver Lodge directed attention to the congestion of work in Section A of the British Association at Leicester. Last week Dr. Chree remarked upon the comparative neglect on our part of such scientific subjects as terrestrial magnetism and the local variations of gravity, which cannot be pursued adequately within the walls of a laboratory, but depend upon observations “in the field.” In the meantime, NATURE has noted Dr. Mill's protest against the scanty opportunity for the discussion of meteorological subjects at Leicester.

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The Advancement of Science

Establishment of microbes in the young ruminant is primarily dependent upon its exposure to an adult animal and having a rumen environment compatible with growth of the microorganisms. The major portion of the rumen microbial population consists of strictly anaerobic bacteria and ciliate protozoa, which appear to account for most of the fermentative activity in this organ. Anaerobic fungi have recently been found also to be normal inhabitants of the rumen; however, they occur in lower concentrations and their ecological niche in the rumen fermentation is uncertain (Chapter 4). Microbial numbers and the composition of the population are affected by a number of factors, of which diet is probably one of the most important. Smaller numbers of facultatively anaerobic bacteria (which may be of importance in very young ruminants), aerobic bacteria, flagellate protozoa and mycoplasmas are also present; however, their contribution to the overall fermentation is considered minimal.

Development of, and natural fluctuations in, rumen microbial populations

Rumen holotrich ciliate protozoa.

Rumen ciliates: their metabolism and relationships with bacteria and their hosts

A protein index for animal feeds is suggested as a basis for the criteria relating nutritive value to chemical composition. The feeds were classified into four main groups: legumes, non-legumes, straws and concentrates. The regression equations for predicting the nutritive value gave a reasonable level of accuracy (0·18–14·74% error). Higher levels of accuracy were attained employing regression equations formulated for more homogenous feed subgroups classified according to their protein and fibre contents. The percentage error resulting from the use of the specific equations was found to range between zero and 9·88.

The prediction of the nutritive value of animal feeds from chemical analyses.

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

1. Four in vitro fermentation experiments, in duplicate, were carried out over 24 hr. periods, to estimate the production of v.f.a. and o.a from forages. 2. A new technique for determining the total organic acids produced in the rumen is described. 3. The o.a. produced in the earlier part of the fermentation are considerably higher than the v.f.a. but the difference then diminishes. There is practically no difference in the amounts produced after 24 hr. 4. Highly significant correlations were found between the in vitro production of v.f.a. or o.a. and d.e./kg. d.m., for all the roughages tested. Nonlegumes gave a more highly significant correlation than legumes. 5. Regression equations show that o.a. or v.f.a. were more accurate than in vitro cellulose digestion for predicting the d.e./kg. d.m. of non-legume forages. It is concluded that V.F.A. production in vitro is the best criterion in this respect.

The use of the in vitro fermentation technique to estimate the digestible energy content of some Egyptian forages II. The in vitro production of total volatile fatty acids and organic acids as criteria of energy content

Summary Fistulated sheep, goats, cattle and buffaloe's were used to study the effect of substituting urea for 0, 36, 55 or 100% of cottonseed cake protein on the total counts, pool size and composition of protozoal population in the rumen. Highest protozoal counts were obtained on the 0 and the 100% urea-N diets and the lowest protozoal counts were observed in 55% urea-N diet. Sheep and goats had higher protozoal counts than buffalo and cattle. Protozoal pool size in the rumen of sheep was greater than of goats and that of buffalo was greater than for cattle. Increasing urea-N in the diet decreased growth rate of protozoa in vitro. The growth rate of protozoa in vitro was affected by postprandial time, but not by animal species. A mixture of Entodinia, Isotricba, Diplodinium and Polyplastron species was found in the rumen contents of all animal species. Entodinia sp. were predominant in all animals on the four diets. Increasing urea-N in the diet increased the percentage of Entodinia and reduced the other species so that negligible numbers of Isotricba, Diplodinium and Polyplastron were observed in 100% urea-N diet. Increased levels of urea increased the generation time (hr) of protozoa in sheep, goats, cattle and buffaloes.

Effect of increased levels of urea in the diet on ruminal protozoal counts in four ruminant species.

A method is described for the determination of rumen volume using Cr-EDTA colour measurement in a spectrophotometer at 550 nm. The results of several determinations of rumen volume comparing this method with Cr-determination as chromate and polyethylene glycol as markers gave similar values with differences ranging from 1 to 14% with an average of 6%. Direct measurements through evacuating rumen contents gave values 20·68% higher than those estimated by the colour method. The values were similar when corrected for dry matter.

M. A. Naga

Papers

The prediction of the nutritive value of animal feeds from chemical analyses.

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

The use of the in vitro fermentation technique to estimate the digestible energy content of some Egyptian forages II. The in vitro production of total volatile fatty acids and organic acids as criteria of energy content

Effect of increased levels of urea in the diet on ruminal protozoal counts in four ruminant species.

A colorimetric technique using chromium-ethylene diamine tetra acetate for measuring rumen volume