Abstract: Eubacterium limosum was isolated as the most numerous methanol-utilizing bacterium in the rumen fluid of sheep fed a diet in which molasses was a major component (mean most probable number of 6.3 X 10(8) viable cells per ml). It was also isolated from sewage sludge at 9.5 X 10(4) cells per ml. It was not detected in the rumen fluid of a steer on a normal hay-grain diet, although Methanosarcina, as expected, was found at 9.5 X 10(5) cells per ml. The doubling time of E. limosum in basal medium (5% rumen fluid) with methanol as the energy source (37 degree C) was 7 h. Acetate, cysteine, carbon dioxide, and the vitamins biotin, calcium-D-pantothenate, and lipoic acid were required for growth on a chemically defined methanol medium. Acetate, butyrate, and caproate were produced from methanol. Ammonia or each of several amino acids served as the main nitrogen source. Other energy sources included adonitol, arabitol, erythritol, fructose, glucose, isoleucine, lactate, mannitol, ribose, valine, and H2-CO2. The doubling time for growth on H2-CO2 (5% rumen fluid, 37 degree C) was 14 h as compared with 5.2 h for isoleucine and 3.5 h for glucose. The vitamin requirements for growth on H2-CO2 were the same as those for methanol; however, acetate was not required for growth on H2-CO2, although it was necessary for growth on valine, isoleucine, and lactate and was stimulatory to growth on glucose. Acetate and butyrate were formed during growth on H2-CO2, whereas branched-chain fatty acids and ammonia were fermentation products from the amino acids. Heat tolerance was detected, but spores were not observed. The type strain of E. limosum (ATCC 8486) and strain L34, which was isolated from the rumen of a young calf, grew on methanol, H2-CO2, valine, and isoleucine and showed the same requirements for acetate as the freshly isolated strains.

Abstract: The fermentation of cellulose by an ovine rumen anaerobic fungus in the absence and presence of rumen methanogens is described. In the monoculture, moles of product as a percentage of the moles of hexose fermented were: acetate, 72.7; carbon dioxide, 37.6; formate, 83.1; ethanol, 37.4; lactate, 67.0; and hydrogen, 35.3. In the coculture, acetate was the major product (134.7%), and carbon dioxide increased (88.7%). Lactate and ethanol production decreased to 2.9 and 19%, respectively, little formate was detected (1%), and hydrogen did not accumulate. Substantial amounts of methane were produced in the coculture (58.7%). Studies with [2-C]acetate indicated that acetate was not a precursor of methane. The demonstration of cellulose fermentation by a fungus extends the range of known rumen organisms capable of participating in cellulose digestion and provides further support for a role of anaerobic fungi in rumen fiber digestion. The effect of the methanogens on the pattern of fermentation is interpreted as a shift in flow of electrons away from electron sink products to methane via hydrogen. The study provides a new example of intermicrobial hydrogen transfer and the first demonstration of hydrogen formation by a fungus.

Abstract: Since Megasphaera elsdenii ferments a variable part of dl-lactate to butyrate, measurement of the percentage of dl-lactate fermented to propionate via the acrylate pathway in rumen contents will underestimate the participation of M. elsdenii in the dl-lactate fermentation. The percentage of dl-[2-13C]lactate fermented via the acrylate pathway and the percentage of dl-lactate fermented to butyrate can be measured with 13C-FT (Fourier transform)-nuclear magnetic resonance. On the average, the contribution of M. elsdenii to dl-lactate fermentation in the rumen of dairy cattle was found to be 74% (standard deviation, 13%), but differed with animal or diet. After feeding a cow readily fermentable carbohydrates, the contribution of M. elsdenii to the fermentation of dl-lactate increased as a consequence of catabolite repression in other dl-lactate-fermenting bacteria.

Abstract: Fermentation of food by the microbial community of the rumen is essential for the maintenance and growth of ruminants. The microbial ecosystem and its interaction with the host are described, along with recent attempts to manipulate the composition and activity of the microbial community by adding antibiotics and other chemicals to ruminant diets. A similar microbial community and fermentation occur in the large intestine or cecum of most nonruminant animals including the large intestine of humans. The microbial ecosystems of the rumen and human large intestine are compared.

Abstract: The action of sodium hydroxide on the rate and extent of loss of wall polysaccharides from wheat and barley straws incubated in the rumen of the sheep was studied using a nylon bag technique. Cellulose loss reached a maximum in straws treated with 10 g NaOH 100 g−1 straw. Further increase in amounts of alkali applied resulted in additional solubilisation of straw constituents, particularly xylan, but did not further enhance cellulose degradation. Rates of degradation of isolated straw, cotton and wood celluloses correlated with three of four measures of cellulose crystallinity obtained by X-ray diffraction and infrared analysis. Treatment of cellulose samples with 20 g NaOH 100 g−1 cellulose did not affect rates of loss or produce detectable changes to cellulose morphology. Loss of acetic acid esters, which accompanied alkali treatment, did not relate to improvements to digestibility. The rate of loss of cellulose from delignified neutral detergent fibre (NDF) was that shown by the isolated straw cellulose, despite the presence of acetylated hemicellulose. Deacetylation of delignified NDF with NaOH or sodium methoxide did not enhance rates of xylose or cellulose loss. In lignified wall material (NDF) the molar ratio acetyl:xylose (approximately 1:3.5) and proportion of the major phenolic acids (p-coumaric and ferulic acids) remained essentially constant throughout the course of degradation in the rumen. It is suggested that loss of phenolic acids, while not directly contributing to digestibility enhancement, may model the susceptibility of ester linkages formed between polysaccharide and polyphenolic material to alkali. The extent of solubilisation of p-coumaric acid produced by NaOH showed a linear relationship with cellulose digestibility. An upper limit of 40% acid detergent lignin and 55% of total phenolics were released by NaOH, the extent of release closely paralleling cellulose digestibility. Phenolic material resistant to alkali remained associated with wall polysaccharides and was not released from nylon bags until over 50% of cellulose (and hemicellulose) had been degraded.

Abstract: Pangola grass (Digitaria decumbens) and Rhodes grass (Chloris gayana) were cut as 6 and 12 week regrowths, dried, chopped, and separated into leaf and stem fractions by using a gravity separator. Each of the eight diets was offered to four cattle and eight sheep fitted with a ruminal cannula to measure voluntary intake and digestibility of the dry matter (DM), organic matter (OM) and neutral detergent fibre (NDF). Possible deficiencies of protein and minerals were minimized in this study by feeding casein and a mineral supplement. The total DM, OM and NDF contents of the rumeno-reticulum (rumen) were measured by manually emptying the rumen and the values used to estimate retention times of DM, OM and NDF. Cattle consumed 35% more leaf than stem fraction. Sheep consumed 21 % more leaf. When the daily voluntary intake was expressed as g/kg0.9 the intake was similar for cattle and sheep. The higher intake of the leaf fraction was associated with the shorter time that it was retained in the rumen of both cattle and sheep. Leaf and stem fractions were digested to the same extent by cattle. There was also no difference in the digestibility of leaf and stem fed to sheep. The digestive efficiency of sheep was 0.033 lower than that of cattle for both DM and NDF. Cattle retained all diets for longer periods in the rumen than did sheep. This difference was associated with the higher digestive efficiency of the cattle. It was concluded that both cattle and sheep consumed more leaf than stem fractions of grasses, and that the higher intake of leaf was associated with the shorter time that it was retained in the rumen and not by differences in digestibility as such.

Abstract: Pangola grass (Digitavia decumbens) and Rhodes grass (Chlovis gayana) cut as 6 and 12 week regrowths were separated into leaf and stem fractions and fed ad libitum to four cattle and eight sheep fitted with ruminal fistulae to determine the importance of particle size in controlling the retention time of feed in the rumeno-reticulum (rumen). Particle size was determined by using a wet sieving technique, and based on the cumulative dry matter distribution on the sieves of faeces from cattle and sheep; all particles >1.18 mm were described as large particles. The proportion of large particles was measured in the chopped diet offered, the masticated diet, the ruminal contents and the faeces. Chopped leaf and stem fractions contained 0.85 and 0.86 g/g large particles respectively. Mastication by cattle reduced the proportion of large particles in leaf and stem to 0.58 and 0.76 (P 0.05) and in cattle 0.272 and 0.345 (P 0.05) for leaf and stem, and in sheep 0.993 and 0.991 (P > 0.05). Large particles in leaf and stem were retained in the rumen of the sheep for 11.0 and 11.7 h (P > 0.05). Cattle retained large particles in all diets for a longer time (P 0.05). Differences in retention time of large particles in the rumen did not appear to be the only factor controlling the retention of dry matter in the rumen and voluntary intake. A model was developed to describe the flow of large and small particles through the rumen. Intake simulation studies indicated that the most important factor influencing dry matter retention time in the rumen was the retention time of small particles (> 1.18 mm). Changes in the rate of breakdown of large particles had a small effect on dry matter retention time.

Abstract: During growth of Bacteroides succinogenes in a liquid medium with cellulose as the source of carbohydrate, greater than 80% of the carboxymethylcellulase (endo-beta-1,4-glucanase), xylanase, and aryl-beta-xylosidase and 50% of the aryl-beta-glucosidase released from cells into the culture fluid. Less than 25% of the cellobiase activity was detected in the culture fluid. Approximately 50% of each of the released enzymes measured was associated with sedimentable subcellular membrane vesicles. The vesicles appeared to be released from the outer membrane of intact cells by bleb formation, primarily in pockets between the cells and the cellulose, although a few unattached cells with blebs were seen. Many vesicles were seen adhering to cellulose, and they were also seen free in the culture fluid. These data suggest that B. succinogenes releases hydrolytic enzymes in nonsedimentable and particulate forms during growth by a mechanism which has until now received little attention. Cellulose incubated in a porous nylon bag in the rumen was colonized by bacteria resembling B. succinogenes, and subcellular vesicles were seen penetrating channels and fractures in the cellulose. On this basis, it is suggested that B. succinogenes cells in the rumen contribute to an extracellular population of subcellular vesicles that possess cellulolytic and hemicellulolytic activities which probably enhance polymer digestion and provide a source of sugars for microbes lacking polymer-degrading activity, thereby contributing to a stable heterogeneous microbial population.

Abstract: 1. The rate of proteolysis of fraction I (18S) leaf protein in the rumen of sheep of cattle was affected by diet ans the rate on fresh lucerne (medicago sativa L) was three to nine times the rate on a hay + concentrate diet. 2. Simultaneous rumen fermentations in vivo and in an artificial rumen showed that the rates of proteolysis of fraction I in vitro was approximately 30% of the rates in sheep. 3. Using 14 C uniformly-labelled fraction I protein at low concentrations, proteolysis exhibited 1st-order kinetics. Over a wide range of protein concentrations the velocity v. substrate concentration curve showed Michaelis-Menten characteristics typical of an enzyme-catalysed reaction. With rumen fluid from a hay + concentrate-fed sheep the maximum velocity was 2.6 mg protein nitrogen/1 per min and the Michaelis constant was 75 mg nitrogen/l. 4. Rapid absorption of 14C-labelled fraction I protein onto bacterial cells preceded proteolysis. 5. Sucrose-density-gradient analysis showed initial incorporation of 14C from protein into rumen bacteria followed by partial transfer to rumen protozoa. 6. No peptides were detected during proteolysis showing that the rate-limiting step occurred during the initial stages of proteolysis. Only small amounts of free amino acids were released except for leucine, isoleucine, valine and ornithine, which showed significantly increased levels. 7. Volatile fatty acids were the main 14C-labelled end products and were rapidly produced in descending concentrations: acetate greater than propionate greater than 3-methyl + 2-methyl butyrate greater than butyrate greater than isobutyrate greater than valerate.

Abstract: 15N tracer methods and gas chromatography coupled to an electron capture detector were used to investigate dissimilatory reduction of nitrate and nitrite by the rumen microbiota of a fistulated cow Ammonium was the only 15N-labeled end product of quantitative significance Only traces of nitrous oxide were detected as a product of nitrate reduction; but in experiments with nitrite, up to 03% of the added nitrogen accumulated as nitrous oxide, but it was not further reduced Furthermore, when 13NO3- was incubated with rumen microbiota virtually no [13N]N2 was produced Acetylene partially inhibited the reduction of nitrite to ammonium as well as the formation of nitrous oxide It is suggested that in the rumen ecosystem nitrous oxide is a byproduct of dissimilatory nitrite reduction to ammonium rather than a product of denitrification and that the latter process is absent from the rumen habitat

Abstract: 1. In a randomized block design, four sheep were given 800 g daily of diets containing: chopped lucerne (L), chopped lucerne-rolled barley (2:1; LB), rolled barley-chopped lucerne (2:1; BL), rolled barley (B); each diet was supplemented with minerals, vitamins and urea as considered necessary. Chronic oxide was included in the diets as a flow marker. 2. Flows of organic matter (OM) and non-ammonia-nitrogen (NAN) to the small intestine (SI) were measured and microbial protein was identified by a 35S-incorporation procedure. 3. OM disappearance in the rumen increased linearly with increasing inclusion of barley in the diet but there was no significant change in microbial NAN flow to the SI so that the yield of microbial NAN (g)/kg fermented OM (FOM) decreased from 29.6 (diet L) to 22.7 (diet B). Changes in the energetic efficiency of microbial protein synthesis appeared to be unrelated to alterations in rumen fluid volatile fatty acid (VFA) proportions or in rumen fluid dilution rate (D). 4. The degradability of dietary protein (non-urea-N), estimated using the 35S procedure, was 0.72, 0.76, 0.86 and 0.86 for diets L, LB, BL and B respectively. Similar values were obtained from concurrent polyester-bag experiments when the fractional outflow rate of undegraded protein from the rumen (k) was assumed to be 0.046.

Abstract: Pangola grass (Digitauia decumbens) and Rhodes grass (Chlouis gayana) cut as 6 and 12 week regrowths were separated into leaf and stem fractions and fed ad libitum to four cattle and eight sheep fitted with ruminal cannulae. Cattle and sheep ate more of the leaf than of the stem fraction, and this was associated with the shorter time that neutral detergent fibre (NDF) was retained in the rumeno-reticulum (rumen). To study this difference, measurements were made of the retention time of lignin, passage rate of undigested NDF and water from the rumen, ruminal water volume, potential digestibility of NDF and rate of digestion of NDF by means of the nylon bag technique and in vivo techniques. Possible deficiencies of protein and minerals were minimized from this study by feeding casein and a mineral supplement. Lignin was used to measure the time that indigestible feed fractions remained in the rumen. The retention time of the NDF was closely correlated with the time lignin was retained in the rumen (r = 0.93, P < 0.01). This indicated that the longer retention time and lower intake found with the stem fraction was associated with the slower rate of passage of NDF through the reticulo-omasal orifice. The longer retention time of NDF by cattle compared with sheep could also be explained in this way. The passage rate constant for water leaving the rumen was slightly higher for cattle and sheep fed on leaf fractions and lower for cattle compared to sheep on all diets. The flow of water from the rumen through the reticulo-omasal orifice was 25 and 22% (P < 0.05) more for cattle and sheep respectively when they consumed leaf compared to when they consumed stem. The concentration of NDF in water passing through the reticulo-omasal orifice was similar for leaf and stem fractions (26 and 27 gl-1. There was a higher frequency of ventral ruminal sac contractions in sheep fed on leaf compared with those eating stem. The potential digestibility of the NDF was higher for leaf than stem fractions (0.658 v. 0.600, P < 0.05). Rates of digestion of leaf and stem samples in nylon bags suspended in the rumen of cattle were similar. Samples that had been masticated had a higher digestion rate constant than chopped grass (0.0216 v. 0.0159, P < 0.05). Digestion rate constants calculated from a rumen model showed large differences both between leaf and stem (0.0488 c. 0.0305, P < 0.05) and between cattle and sheep (0.0307 v. 0.0486, P < 0.05). It was suggested that the higher digestion rate constant calculated from a rumen model compared with the nylon bag method was due to additional mastication during rumination. It was concluded that the higher voluntary intake and shorter retention time in the rumen of the leaf than of the stem fraction of grasses was associated with an apparent higher rate of digestion of NDF in vivo, the higher rate of passage of the NDF from the rumen and the higher potential digestibility of the leaf. Sheep were found to retain NDF in the rumen for a shorter time than cattle, and this difference also was associated with a higher rate of digestion of the NDF and more rapid rate of passage of the NDF.

Abstract: 1. A long-term experiment was made with the Rumen Simulation Technique (Rusitec), in which the fermentation of a mixed ration of hay (10 g/d) and bruised barley (5 g/d) was compared with the fermentation of the same diet in the presence of 2, 10 and 50 mg monensin/d. 2. Monensin depressed the production of acetic and butyric acids, markedly increased the production of propionic acid and virtually, eliminated the production of isovaleric acid. The production of methane was decreased in the presence of monensin, but this decrease could be accounted for entirely by the changes in the production of volatile fatty acids and redistribution of metabolic hydrogen. 3. The digestibility of dry matter (DM) in the rations declined in the presence of monensin. Determinations of the rates of digestion showed that the digestion of the readily-fermented food in the initial stages was not affected by monensin, but that at 24 h digestion had been inhibited by monensin. The inhibition was due entirely to its effect on the digestion of the fibrous components. Digestion of non-fibrous material was not affected. 4. The efficiency of microbial growth, expressed as g dry weight/mol ATP formed (YATP) and in terms of DM digested, tended to be increased by monensin. This however occurred only at high, non-practical doses. 5. Urease (EC 3. 5. 1. 5) was induced by the addition of urea of the fermentation, but monensin had no effect on urease activity. Although monensin increased the activity of protease in washed suspensions, more food protein apparently escaped degradation. This may have been due to decreased deaminative activity. 6. Monensin altered the microscopic appearance of the fermentation fluid, and changed the activity of some enzymes in sonicated extracts, including alkaline phosphatase (EC 3. 1. 3. 1), acetate kinase (EC 2. 7. 2. 1) and succinate dehydrogenase (EC 1. 3. 99. 1). These results are discussed in terms of known sensitivities of rumen microbes to monensin and their contribution to the fermentation as a whole.

Abstract: Eleven isolates of Bacteriodes succinogenes were obtained from the rumen of a cow by an enrichment method with dewaxed cotton fibers as the selective substrate. All of the isolates degraded cotton fibers, but none formed clear zones in cellulose agar, having only a limited ability to degrade the type of cellulose powder used. One isolate, BL2, was studied in greater detail and was found to accumulate a glycogen-like polysaccharide when excess (0.5 to 1.0%) soluble carbohydrate was supplied in the nutrient medium. Although the pattern of growth and polysaccharide accumulation by strain BL2 changed during maintenance of the organism in the laboratory, the maximum amount of carbohydrate found in the cells was constant, at around 74% of the cell dry weight. The findings are discussed in relation to the methods of assessing the role of B. succinogenes in the rumen fermentation.

Abstract: The effect of rumen ammonia concentration on microbial protein synthesis and fermentation was studied in three separate experiments. In each experiment three separate sheep were fed semi-purified diets [designated A (‘concentrate’), B (‘roughageconcentrate’) or C (‘roughage’)] and infused intra-ruminally with five graded amounts of urea according to a randomised block design. Rumen ammonia concentrations remained low until the total nitrogen intake was about 10 g day−1 after which rumen ammonia concentration rose rapidly. Rumen and duodenal ammonia concentrations were linearly related (r=0.90, 0.98 and 0.84 for diets A, B and C, respectively; P< 0.001). Microbial protein production did not increase when rumen ammonia concentrations exceeded 2.8 mM for diet A, 6.0 mM for diet B and 1.6 mM for diet C. Diets A and C produced a propionate-type fermentation while diet B was characterised by an acetate-type fermentation. Rumen ammonia concentration had no apparent effect on either concentration or the molar proportions of volatile fatty acids. There were no systematic trends in digestibility in relation to rumen ammonia concentration.

Abstract: Studies were carried out to determine the means by which holotrich protozoa can maintain their numbers within the rumen against the washout effect associated with the flow of ingesta. When a diet composed of 2 kg of concentrate and 1.5 kg of rice straw was fed to Holstein cows, about a fourfold increase in holotrich numbers per ml of rumen fluid was observed within 1 h after the commencement of feeding, and an abrupt decrease followed. This fluctuation in numbers was not related to the time of feeding. A sole feeding of 2 kg of concentrate had almost the same effect on the holotrichs as a sole feeding of 1.5 kg of rice straw. Administration of either 2 kg of concentrate or 1.5 kg of rice straw through the rumen fistula caused similar changes, though the extent of response to the former was greater than that to the latter. The administration of either 0.7 kg of starch or 0.2 kg of glucose through the fistula had a relatively minor effect on the holotrich population. Addition of rice straw to 0.5 kg of concentrate increased the change in numbers, but its addition had little, if any, effect when 1 kg of concentrate was fed. These results suggested that the fluctuation in holotrich numbers was related not only to the nature or component of feed but also to other factors such as the quantity or volume of a diet and the act of ingesting feed. Increasing the number of feedings up to eight times per day at 3-h intervals caused a decrease in the peak heights of holotrich numbers per milliliter of rumen fluid. A thick protozoal mass which primarily consisted of holotrichs was found on the wall of the reticulum of Holstein steers slaughtered after overnight starvation. These findings suggest that holotrichs would usually sequester on the reticulum wall and migrate into the rumen only for a few hours after feeding, and that this mode of behavior would be essential for holotrichs to maintain their population within the rumen of cattle. Possible mechanisms of the migration are also discussed.

Abstract: Mixed cultures of rumen bacteria were inoculated into anaerobic buffer solutions containing mixed carbohydrates, casein and ammonia, and rates of bacterial growth, protein degradation, ammonia formation or utilization and lactate production were determined Bacterial growth rate was varied by the provision of excess carbohydrate (one large dose at the onset of the incubation) or limited carbohydrate (small doses every hour or every 2 hr) When carbohydrate was limited, growth rate was slow, the extent of protein degradation was small and lactate did not accumulate in the fermentation vessels Lactate production and protein degradation were also negligible during the initial phases of the high carbohydrate, fast growth rate incubations, but large increases in each were seen after 3 hours Microscopic examination of the fast growth incubations revealed large numbers of small ovoid cells similar to Streptococcus bovis, while tha slow growth incubations exhibited a variety of morophological types and very few small ovoid cells Because the lactic acid and morphological data suggested that proliferation of S bovis might be responsible for rapid proteolysis, effects of gram-positive antibiotics were examined When compared against a fast growth control, both thiopeptin (5 ppm) and monensin (5ppm) were found to decrease protein degradation, but the inhibition by thiopeptin (50%) was greater than that by monensin (13%) The ratios of protein degraded to bacteria protein synthesized were 659, 362 and 628 for the control, thiopeptin and monensin treatments, respectively Actively proteolytic strains of S bovis were isolated from fast growth incubations, and subsequent experiments showed that the ratio of protein degraded to bacterial protein synthesized was approximately 150 Collectively, the data indicate that S bovis is a very proteolytic rumen bacterium

Abstract: The artificial fibre bag technique has been widely used in studies of forage dry-matter digestibility (Van Keuren & Heinemann, 1962) and of the release of a range of plant constituents during fermentation in the rumen (Playne, McLeod & Dekker, 1972). More recently, the technique has been promoted as a simple means of estimating the rate and extent of food protein degradability in the rumen (θrskov & Mehrez, 1977; Mathers, Horton & Miller, 1977).

Abstract: An anaerobic butyrate-degrading bacterium, morphologically similar to Syntrophomonas wolfei, was isolated in coculture with Desulfovibrio strain G11 from an enrichment of bovine rumen fluid. A Methanosarcina species was the major H2-using organism in the enrichment. The results are discussed in relationship to the absence of Methanospirillum hungatei, the H2-using methanogen usually found in association with S. wolfei, and the finding of Methanosarcina rather than Methanobrevibacter ruminantium as the major H2-using bacterium in the enrichments. The finding of butyrate degraders in the rumen suggests that, if the retention time of the rumen contents becomes more prolonged, butyrate and longer-chained fatty acids might be significantly degraded.

Abstract: 1. The effects of a methane inhibitor, ICI 111075, and a propionate enhancer, monensin, were studied using in vitro continuous fermenters. 2. Both compounds increased the yield of substrate energy, carbon and hydrogen in volatile fatty acids (VFA). This was mainly due to an increase in the molar proportion of propionic acid. 3. Improved yields of VFA were accompanied by reductions in methane production and microbial yield. 4. Since published information showed that monensin reduced rumen dilution rate in vivo an analogous in vitro system was proposed in which a high dilution rate control fermenter was compared with a monensin treated fermenter set to run at a low dilution rate. 5. Results showed that the general intrinsic microbial activity of the chemical manipulators was not affected by changes in dilution rate. Changing dilution rate in addition to chemical treatment however resulted in substantial modifications in the net effect on the fermentation. 6. The practical implications of reducing rumen dilution rate as a side effect of chemically manipulating the rumen fermentation could involve changes in food intake, increased importance of secondary fermentations and a reduced effect of nutrients not degraded in the rumen.

Abstract: Hay made from the tropical forage legume Lablab purpureus was chopped and separated into leaf and stem fractions by using a gravity separator. Each diet was fed to four cattle and six sheep fitted with rumen fistulae to measure the digestibilities of the dry matter (DM), organic matter (OM) and neutral detergent fibre (NDF), and the retention times of DM, OM and NDF in the rumeno-reticulum (rumen) and the rumen volume. Mean voluntary intake of the DM in the leaf fraction was 79 % higher by cattle and 61 % higher by sheep than the stem fraction, and this appeared to be associated with the shorter time it was retained in the rumen. Both leaf and stem DM were digested to a similar extent by cattle. Sheep digested the leaf fraction to the same extent as cattle. However, the DM digestibility of the stem eaten by sheep was 0,061 lower than that of the leaf fraction (P < 0.05). Cattle retained the DM, OM and NDF in all diets for longer periods in the rumen than did sheep. This difference led to a 48% higher voluntary intake (g(kg body d-1) by sheep. The proportion of large particles that disappeared within the rumen was lower (P < 0.01) for cattle (0.968) than for sheep (0.994). The large particles of the leaf and stem fraction were retained for the same mean time by sheep (5.7 and 5.6 h), which was shorter (P < 0.01) than the corresponding times for cattle (13.8 and 21.6 h). The rate of disappearance of large particles in the rumen appeared to be only a minor factor causing the longer retention time of stem fractions in the rumen. The concentrations of volatile fatty acids and ammonia in the rumen were higher for leaf than stem fractions with no differences between cattle and sheep. The proportion of acetic acid for cattle (0.75) was higher (P < 0.05) than that for sheep (0.69) while the corresponding propionic acid proportions were lower (P < 0.01) in cattle (0.14) compared with sheep (0.19). These differences were associated with a higher passage rate constant for water flowing from the rumen and a higher digestion rate constant in sheep. It was concluded that both cattle and sheep ate more of the leaf than the stem fraction of the legume Lablab purpureus and that the higher intake of leaf was associated with the shorter time that it was retained in the rumen and was not due to differences in digestibility. Cattle had a smaller relative voluntary intake of legume than sheep, a difference that was associated with the longer time that digesta was retained in the rumen.

Abstract: Comparative studies on the effect of diet on ruminal protein degrading activity were made with sheep fed either maize or timothy and with sheep fed either barley or lucerne. In both studies the levels of proteolytic activity and deaminase activity in the rumen, measured as non-protein nitrogen and ammonia production, respectively, during in-vitro incubation of rumen liquor and casein, were higher when cereal was given than when forage was given. The rate of casein degradation after intra-ruminal infusion was also higher with the cereal diets, whereas outflow rate from the rumen was lower. However, with all diets the fractional hydrolysis rate of casein was considerably greater than its fractional outflow rate and the calculated proportion of protein escaping ruminal breakdown was low. The effect of diet on the degradation of the protein of natural feedstuffs was examined by measuring N disappearance when samples of the four feeds and of three protein supplements (soya bean meal, groundnut meal and fish-meal) were incubated in dacron bags in the rumen. In contrast to the findings with casein, the rate of N disappearance for all feedstuffs, except maize which was similar on the two types of diet, was lower when sheep were given cereal than when given forage.