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

Bovine Acidosis: Implications on Laminitis

Chemical factors involved in ruminal fiber digestion.

Certain indigestible oligosaccharides may benefit gastrointestinal tract health via fermentation and proliferation of desirable bacterial species. The purpose of this study was to elucidate effects of selected oligosaccharides on cecal and fecal short-chain fatty acid (SCFA) concentration, pH, total large bowel wet weight and wall weight, and gut microbiota levels in rats. Fifty male Sprague-Dawley rats were randomly assigned to one of five treatments: 1) control diet; 2) control diet + 5% microcrystalline cellulose (5% CC); 3) control diet + 5% CC + 6% fructooligosaccharides; 4) control diet + 5% CC + 6% oligofructose; or 5) control diet + 5% CC + 6% xylooligosaccharides. The control diet consisted of (dry matter basis) 20% protein, 65% carbohydrate, 10.5% fat, vitamin and mineral mixes. The duration of the study was 14 d. The oligofructose- and fructooligosaccharide-containing diets resulted in higher cecal butyrate concentrations compared with the control, cellulose and xylooligosaccharide diets. Generally, total cecal SCFA pools were higher while pH was lower from ingesting oligosaccharide-containing diets compared with control or cellulose diets. Cecal total weight and wall weight were higher from oligosaccharide consumption, whereas colonic total wet weight was higher for rats consuming xylooligosaccharides compared with other treatments; colon wall weight was unaffected by treatments. Cecal bifidobacteria and total anaerobes were higher whereas total aerobes were lower in rats fed oligosaccharide diets compared with those fed the control diet. Cecal lactobacilli levels were unaffected by treatment. Dietary incorporation of fermentable, indigestible oligosaccharides, by providing SCFA, lowering pH, and increasing bifidobacteria, may be beneficial in improving gastrointestinal health.

Selected Indigestible Oligosaccharides Affect Large Bowel Mass, Cecal and Fecal Short-Chain Fatty Acids, pH and Microflora in Rats

In situ and Other Methods to Estimate Ruminal Protein and Energy Digestibility: A Review

A stepwise adaptation was carried out on eight sheep through diets containing 10, 24, 44, 60 to a final diet containing 71% maize meal and molasses. The numbers of protozoa in the rumen increased in proportion to amount of readily fermentable carbohydrate fed, up to and including the 60% grain and molasses diet, while the numbers of total culturable bacteria remained essentially constant. However, the proportions of amylolytic and lactate-utilizing bacteria increased, and there was an orderly shift from acid-sensitive to more acid-tolerant species, particularly amongst the lactate-utilizers in response to the gradual decrease in the ruminal pH. Up to this stage the protozoa probably controlled the rate of fermentation by engulfing starch grains and bacteria and were thus able to maintain the pH of the rumen above 5·5. Lactic acid appeared only transiently and the peak values tended to diminish as adptation progressed.The first day the final diet was fed the ruminal pH decreased to 5·4 or below for several hours. Within 7 days the number of protozoa had decreased by 50–80% and the number of total culturable bacteria increased sharply. Conditions in the rumen became unstable: peak values of D- and L- laotic acid increased by ca. 0·5 HIM, the acetate/propionate ratio decreased to ca. 2 and peak glucose concentration increased t o 3·2–9·5 mM. One animal refused all food for 1 day. Acid-tolerant species of lactate-utilizing bacteria multiplied rapidly in response to the increased production of ruminal lactic acid and the ratio of amylolytics to lactate-utilizers decreased from a mean of 10·7 to 3·6. This controlled the increase in lactic acid and the decrease in ruminal pH, allowing the ciliate protozoa to proliferate and regain control of the fermentation.The types of cellulolytic bacteria did not change during the experiment. Despite their acid sensitivity, the number of cellulolytic bacteria per gram of ingesta was of the same order after 54 days on the 71% grain and molasses diet (0·5–13·3 × 107) as on the initial high roughage diet (3·2–7·6 × 107).Three sheep which bloated showed no marked chemical or microbiological differences from the non-bloating animals.

Microbiological and chemical changes in the rumen during the stepwise adaptation of sheep to high concentrate diets

The ruminal metabolism of lactic acid was investigated in vivo under normal feeding conditions in four sheep each adapted to one of the following diets: high-concentrate, intermediate, high-roughage containing 65, 43 or 10% maize meal and molasses respectively, or lucerne hay. A continuous basal turnover of ruminal lactate (0·01–0·02 mmol/1/min) was found which increased 10- to 40-fold immediately after feeding when production exceeded utilization and lactate accumulated in the rumen. This was followed by an increase in utilization rate which removed the accumulated lactate. Both lactate and glucose turnover were related to the amount of readily fermentable carbohydrate in the diet. Approximately 8, 6·5, 5 and 2·5% of the total VFA was formed through lactate on the high-concentrate, intermediate, high-roughage and lucerne hay diets respectively.Rumen microbial counts of total culturable, glucolytic, amylolytic and lactateutilizing bacteria, and of ciliate protozoa were also performed on the four sheep. Numbers of micro-organisms in all groups were highest on the high-concentrate diet and lowest on the two roughage diets. The proportions of the predominant genera from the different metabolic groups of bacteria differed, although in most cases the same organisms were present in the rumen on all diets. The succinate pathway was found to be quantitatively more important in the conversion of lactate to propionate in the rumen. Although the numbers of lactate-utilizing bacteria increased as the amount of RFC in the diet increased, their metabolic activity was actually lower. Reasons for this finding are discussed, together with factors influencing the regulation of lactate production and utilization in the rumen.

An in vivo study of ruminal micro-organisms influencing lactate turnover and its contribution to volatile fatty acid production

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R. I. Mackie

Papers

Microbiological and chemical changes in the rumen during the stepwise adaptation of sheep to high concentrate diets

An in vivo study of ruminal micro-organisms influencing lactate turnover and its contribution to volatile fatty acid production

Microbiology of feed samples incubated in nylon bags in the rumen of sheep