Diurnal variations in bacterial numbers and fluid parameters in ruminal contents of animals fed low- or high-forage diets.

Differential carbohydrate media and anaerobic replica plating techniques were used to assess the degrees of diurnal variations in the direct and viable cell counts as well as the carbohydrate-specific subgroups within the mixed rumen bacterial populations in cattle fed maintenance (metabolizable energy) levels of either a high-forage or a high-concentrate diet once daily. The rumen was sampled at 1 h before feeding and 2, 4, 8, 12, and 16 h after feeding, and selected microbiological parameters of the isolated bacterial populations were assessed. Corresponding samples of ruminal fluid were assayed for fermentation acids, carbohydrate, ammonia, and pH changes. The data showed that regardless of diet, total bacterial numbers remained fairly constant throughout the day. The number of viable bacteria declined 40 to 60% after feeding and then increased to a maximum at 16 h postfeeding. Changes occurred in the carbohydrate-specific subgroups within the bacterial populations, and some of the changes were consistent with a predicted scheme of ruminal feedstuff carbohydrate fermentation. Regardless of diet, however, soluble-carbohydrate-utilizing bacteria predominated at all times. Xylan-xylose and pectin subgroups respectively comprised about one-half and one-third of the population when the high-forage diet was given. These subgroups, along with the cellulolytics, constituted lesser proportions of the population when the high-concentrate diet was given. The cellulolytic subgroup was the least numerous of all subgroups regardless of diet but followed a diurnal pattern similar to that predicted for cellulose fermentation. There were few diurnal variations or differences in bacterial cell compositions and ruminal fluid parameters between diets. The observed similarities and dissimilarities of the rumen bacterial populations obtained when the two diets were given are discussed. The data are consistent with the versatility and constancy of the rumen as a stable, mature microbial system under the specific low-level feeding regimens used.     

Changes in the jugular haematocrit of sheep during feeding.

Intact and splenectomized sheep with and without a rumen fistula were used to investigate changes in the jugular blood haematocrit and plasma osmolality during hourly and once-daily feeding regimes. Osmolality was also estimated in the ruminal fluid of fistulated sheep with spleens. Haematocrit decreased in sheep with spleens before they were given a once-daily feed; it increased when these sheep started to feed, reaching a maximum increase of 13% after 30 min of feeding; it decreased during the remaining 45 min of feeding time and usually continued to decrease after feeding stopped. These changes were not due to diurnal influences. Splenectomized sheep fed once daily showed only small decreases in haematocrit before they were fed. Increases occurred with the onset of eating but they were smaller (7%) than in intact sheep and were of shorter duration. In hourly fed sheep with spleens, haematocrit decreased in the early stages of sampling in a manner similar to that for sheep fed once daily. The changes in haematocrit that did occur were not related in any obvious manner to the feeding regime. The haematocrit in splenectomized sheep fed hourly was stable throughout feeding. Variations in the haematocrit in splenectomized sheep, equivalent to a range of 13% in one of them, were observed in a series of blood samples obtained during a 5-h period remote from the feeding time. Large increases occurred in osmolality of ruminal fluid when sheep were fed daily and this was abolished by hourly feeding. Plasma osmolality in sheep fed once daily increased slowly. Maxima occurred after 100 min from the start of eating and were 7% greater than prefeeding values. Only minor changes were observed when these sheep were fed hourly.     

Diurnal changes in concentration of rumen ciliates and in occurrence of dividing forms in water buffalo (Bubalus bubalus) fed once daily.

When buffalo were fed once daily, significant diurnal variations in concentration of rumen ciliates and occurrence of dividing protozoa were found. Differences in proportions of dividing Entodinium- and Diplodinium-type ciliates were also observed. Results obtained suggest that the range of diurnal fluctuations in rumen protozoa concentration may be related to the percentage of dividing cells in populaitons of these organisms.     

Diurnal changes in concentration of rumen ciliates and in occurrence of dividing forms in water buffalo (Bubalus bubalus) fed once daily.

When buffalo were fed once daily, significant diurnal variations in concentration of rumen ciliates and occurrence of dividing protozoa were found. Differences in proportions of dividing Entodinium- and Diplodinium-type ciliates were also observed. Results obtained suggest that the range of diurnal fluctuations in rumen protozoa concentration may be related to the percentage of dividing cells in populaitons of these organisms.     

Diet Alters Both the Structure and Taxonomy of the Ovine Gut Microbial Ecosystem

We surveyed the ruminal metagenomes of 16 sheep under two different diets using Illumina pair-end DNA sequencing of raw microbial DNA extracted from rumen samples. The resulting sequence data were bioinformatically mapped to known prokaryotic 16S rDNA sequences to identify the taxa present in the samples and then analysed for the presence of potentially new taxa. Strikingly, the majority of the microbial individuals found did not map to known taxa from 16S sequence databases. We used a novel statistical modelling approach to compare the taxonomic distributions between animals fed a forage-based diet and those fed concentrated grains. With this model, we found significant differences between the two groups both in the dominant taxa present in the rumen and in the overall shape of the taxa abundance curves. In general, forage-fed animals have a more diverse microbial ecosystem, whereas the concentrate-fed animals have ruminal systems more heavily dominated by a few taxa. As expected, organisms from methanogenic groups are more prevalent in forage-fed animals. Finally, all of these differences appear to be grounded in an underlying common input of new microbial individuals into the rumen environment, with common organisms from one feed group being present in the other, but at much lower abundance.     

Lotus corniculatus condensed tannins decrease in vivo populations of proteolytic bacteria and affect nitrogen metabolism in the rumen of sheep

Condensed tannins in forage legumes improve the nutrition of sheep by reducing ruminal degradation of plant protein and increasing crude protein flow to the intestine. However, the effects of condensed tannins in forage legumes on rumen bacterial populations in vivo are poorly understood. The aim of this study was to investigate the specific effects of condensed tannins from Lotus corniculatus on four proteolytic rumen bacteria in sheep during and after transition from a ryegrass (Lolium perenne)-white clover (Trifolium repens) diet (i.e., low condensed tannins) to a Lotus corniculatus diet (i.e., higher condensed tannins). The bacterial populations were quantified using a competitive polymerase chain reaction. Lotus corniculatus was fed with or without ruminal infusions of polyethylene glycol (PEG), which binds to and inactivates condensed tannins, enabling the effect of condensed tannins on bacterial populations to be examined. When sheep fed on ryegrass-white clover, populations of Clostridium proteoclasticum B316T, Butyrivibrio fibrisolvens C211a, Eubacterium sp. C12b, and Streptococcus bovis B315 were 1.5 x 10(8), 1.1 x 10(6), 4.6 x 10(8), and 7.1 x 10(6) mL(-1), respectively. When the diet was changed to Lotus corniculatus, the average populations (after 8-120 h) of C. proteoclasticum, B. fibrisolvens, Eubacterium sp., and S. bovis decreased (P < 0.001) to 2.4 x 10(7), 1.1 x 10(5), 1.1 x 10(8), and 2.5 x 10(5) mL(-1), respectively. When PEG was infused into the rumen of sheep fed Lotus corniculatus, the populations of C. proteoclasticum, B. fibrisolvens, Eubacterium sp., and S. bovis were higher (P < 0.01-0.001) than in sheep fed Lotus corniculatus without the PEG infusion, with average populations (after 8-120 h) of 4.9 x 10(7), 3.8 x 10(5), 1.9 x 10(8), and 1.0 x 10(6), respectively. Sheep fed the Lotus corniculatus diet had lower rumen proteinase activity, ammonia, and soluble nitrogen (P < 0.05-0.001) than sheep that were fed Lotus corniculatus plus PEG. The Lotus corniculatus diet reduced rumen nitrogen digestibility (P < 0.05) and ammonia pool size and increased the flow of undegraded feed nitrogen to the abomasum. The nitrogen intake, rumen non-ammonia nitrogen pool size, rumen microbial non-ammonia nitrogen pool size, and abomasal microbial non-ammonia nitrogen fluxes were similar both in sheep fed only Lotus corniculatus and in sheep fed Lotus corniculatus plus PEG, but nonmicrobial non-ammonia nitrogen flux to the abomasum was higher (P < 0.01) for the sheep fed only Lotus corniculatus. Although condensed tannins in Lotus corniculatus reduced the populations of some proteolytic bacteria, total ruminal microbial protein and microbial protein outflow to the abomasum were unchanged, suggesting a species-specific effect of condensed tannins on bacteria in the rumen.     

Assessment of ciliates in the sheep rumen by DGGE

AIMS: This work was carried out to develop a rapid molecular profiling technique to screen ciliate populations in the rumen of sheep. METHODS AND RESULTS: DGGE was used to study the ciliate diversity in the rumen of sheep. There was considerable variation between sheep which were co-housed, and fed the same diet. However, no difference in the major banding patterns was detected, when samples were collected from a single sheep sampled at different points. Following dietary changes, use of a pair-wise comparison of lanes, demonstrated that although there was still diversity between the ciliate population of sheep, the effects as a result of dietary changes were greater. CONCLUSIONS: The technique generated molecular profiles which are sufficiently different to allow comparison between samples, and to permit molecular ecological studies on the rumen ciliate population. SIGNIFICANCE AND IMPACT OF THE STUDY: The outcome of this study means that ciliate diversity in the rumen may now be studied by those unfamiliar with morphological identification of these organisms.     

Feeding behavior, rumination, reticulo-ruminal fermentation and plasma volatile fatty acids, compared in goats and sheep; influence of the diet

Two-year old Alpine she-goats (n = 3) and Texel ewes (n = 3) were compared as to eating behaviour, rumination and volatile fatty acids (VFA) in rumen and blood. The animals were fed once daily with two different proportions (20 and 80%) of barley and hay. Dry matter intake was fixed at 48 g D.M/kg P0.75 per day. In similar feeding and environmental conditions, eating behaviour and rumination of goats and sheep did not differ much: the goats tended to eat faster and there were more rumination periods in the sheep. Latency time, mean duration of rumination periods, daily rumination time and circadian pattern of rumination did not differ significantly between the two species (fig. 1). With both diets we observed a higher VFA concentration and a lower acetate/propionate ratio in the rumen of the ewes; however, rumen pH was lower only in those eating the 80% barley ration (fig. 2). Blood VFA in the jugular vein did not differ between sheep and goats (fig. 3). The proportion of cereals and hay in the diets affected rumen fermentation and rumination pattern in both species. With a higher concentrate/roughage ratio, rumen and plasma VFA increased, while the pH and acetate/propionate ratio in the lumen juice, the number of rumination periods and daily rumination time decreased. When the animals were fed the 80% barley ration, there was practically no rumination in the first 9 h after the single meal. During this time, rumen pH was minimal and VFA levels in the rumen and blood were maximal.     

Ruminal fermentation characteristics and microbial nitrogen assimilation in sheep fed differently composed grass silages

The investigation aimed at examining if the composition of grassland silage affects the microbial nitrogen assimilation in the rumen of sheep. The silages were made of vegetative summer re-growths consisting of 48% grasses, 28% legumes and 24% other forbs (GCF) or of pure grass (G). Silage GCF contained more intermediately degradable non-structural and less slowly degradable carbohydrates, more crude protein (CP), a narrower ratio between slow and very slow degradable nitrogen (N), and exhibited higher in situ degradability of organic matter and CP than Silage G. Four adult wethers equipped with rumen fistulae were used in a two factorial trial. Feed was offered either as silage alone or as a mixture of silage and barley (60:40). Microbial N was estimated using continuous intraruminal 15N infusion and measurement of 15N-enrichment in microbes isolated from rumen liquor samples. With the exception of trends for ruminal butyrate concentrations, no interactions were detected between silage and barley feeding. Sheep receiving Silage GCF exhibited larger diurnal fluctuations of ammonia, and produced more microbial N (p < 0.05) than sheep on Silage G. Feeding the silages with barley decreased ruminal pH and elevated the concentrations of butyrate (p < 0.05). The 15N incorporation into microbial N was reduced by barley feeding (p < 0.05) along with a trend to accelerated rumen fluid turnover, resulting in similar microbial N yields as found in sheep receiving silage without barley. It is concluded that the larger and better balanced amounts of intermediately degradable carbohydrate- and N-containing fractions favoured the ruminal microbial protein synthesis in sheep consuming Silage GCF instead of Silage G.     

Effect of the tropical forage calliandra on microbial protein synthesis and ecology in the rumen

AIMS: To determine the effect of condensed tannins in Calliandra calothyrsus (calliandra) on rumen microbial function. METHODS AND RESULTS: Microbial populations, ruminal protein synthesis and fermentation end-products were measured in sheep fed roughage hay supplemented with calliandra (30%), with and without inclusions of polyethylene glycol (PEG) to counteract the effect of tannin. Molecular and conventional enumeration techniques were used to quantify rumen bacteria, fungi and protozoa, and protein synthesis was predicted from estimates of urinary purine excretion. The total number of cellulolytic bacteria, including populations of Fibrobacter succinogenes and Ruminococcus spp., was significantly lower in sheep supplemented with calliandra and these populations increased when animals were treated with PEG. By contrast, protozoa and fungi and the microbial group containing Bacteroides-Porphyromonas-Prevotella bacteria appeared to be less affected. The efficiency of microbial protein synthesis in the rumen was not altered significantly. CONCLUSION: Calliandra caused significant shifts in rumen microbial populations without changing the efficiency of protein synthesis. SIGNIFICANCE AND IMPACT OF THE STUDY: The effect of calliandra tannins on rumen digestion may result more from complexing with nutrients than direct inhibition of micro-organisms.     

Comparison of microbial fermentation of high- and low-forage diets in Rusitec, single-flow continuous-culture fermenters and sheep rumen

Eight Rusitec and eight single-flow continuous-culture fermenters (SFCCF) were used to compare the ruminal fermentation of two diets composed of alfalfa hay and concentrate in proportions of 80 : 20 (F80) and 20 : 80 (F20). Results were validated with those obtained previously in sheep fed the same diets. Rusitec fermenters were fed once daily and SFCCF twice, but liquid dilution rates were similar in both types of fermenters. Mean values of pH over the 12 h postfeeding were higher (P < 0.001) in Rusitec than in SFCCF, with diet F80 showing higher values (P < 0.001) in both types of fermenters. Concentrations of total volatile fatty acids (VFA) were higher (P < 0.001) in SFCCF than in Rusitec, and in both systems were higher (P = 0.002) for diet F20 than for diet F80. There were significant differences between systems in the proportions of the main VFA, and a fermentation system × diet interaction (P < 0.001) was detected for all VFA with the exception of valerate. No differences (P = 0.145) between the two types of fermenters were detected in dry matter (DM) digestibility, but NDF, microbial N flow and its efficiency were higher (P = 0.001) in SFCCF compared to Rusitec. Whereas pH values and VFA concentrations remained fairly stable through the day in both in vitro systems, pH dropped and VFA increased shortly after feeding in sheep rumen reaching the minimum and maximal values, respectively, about 4 h after feeding. Both in vitro systems detected differences between diets similar to those found in sheep for liquid dilution rate, pH values, DM digestibility, microbial N flow and growth efficiency. In contrast, acetate/propionate ratios were lower for diet F20 than for F80 in sheep rumen (2.73 and 3.97) and SFCCF (3.07 and 4.80), but were higher for diet F20 compared to F80 (4.29 and 3.40) in Rusitec, with values considered to be unphysiological for high-concentrate diets. In vivo NDF digestibility was affected (P = 0.017) by diet, but no differences between diets (P > 0.05) were found in any in vitro system. A more precise control of pH in both types of fermenters and a reduction of concentrate retention time in Rusitec could probably improve the simulation of in vivo fermentation.     

Evaluation of a Method of Measuring Fermentation Rates and Net Growth of Rumen Microorganisms

The method of el-Shazly and Hungate for measuring gas production in rumen contents was slightly modified and used throughout this investigation. The variation in the fermentation rates due to samples collected separately from a sheep fed on hay was less than 2%. When samples obtained through a stomach tube were compared with samples collected through the rumen fistula, the variation was about 3%. The rates of gas and acid production were approximately similar in samples obtained from the rumen at the same time when no sodium bicarbonate was added. During in vitro incubation of whole ruminal contents, there was a highly significant correlation between the net growth rate values (obtained by using fermentation capacity as an index) and the change in concentration of viable rumen bacteria or total ciliate protozoa.     

Effects of Changes in Feed Level, Starvation, and Level of Feed After Starvation Upon the Concentration of Rumen Protozoa in the Ovine

Four rumen fistulated sheep were used in five experiments to investigate the effect of feed level upon the concentration of rumen ciliate protozoa. The sheep were fed once daily 650 g of a pelleted diet composed of corn cobs, 45%; alfalfa meal, 35%; oats, 12.5%; cane molasses, 5%; urea, 0.4%; and vitamins and minerals, 2%. The concentration of protozoa reached minimum and maximum values at 5 and 22.5 h after feeding, respectively. Thus, to estimate apparent generation rates, concentrations of protozoa were determined at 5 and 20 h postfeeding. Apparent generation rate/h = natural log of ([concentration of protozoa at 20 h divided by concentration at 5 h] divided by the time interval, [T20 to T5]). Alteration of the feed to protozoa ratio by starvation and by changing the level of feed (200 to 900 g/day) showed that as the ratio of feed to protozoa increased, generation rate increased. Measurements of liquid turnover rates in the rumen showed that turnover rate decreased as feed level decreased. Turnover rate was near zero when the sheep were starved. Small quantities of soluble substrates, added directly to the rumen of starved sheep, maintained the protozoal population when rumen turnover was minimal. Furthermore, as rumen turnover rate increased with increased levels of feed, the effect of substrate on maintaining the protozoal population was negated. Thus, at high feed levels, turnover rate may be the dominant factor controlling the establishment and concentration of protozoa in the rumen.     

Effect of feeding regimen on diurnal variation of breathing movements in late-gestation fetal sheep

There is a diurnal variation in the mean incidence and amplitude of fetal breathing movements (FBMs) in sheep after approximately 120 days gestation. To determine whether this variation is caused by diurnal fluctuations in plasma glucose or prostaglandin (PG) concentrations, we studied two groups of pregnant sheep fed either once daily at 1100 h or every 2 h for 24 h. Maternal and fetal blood samples were taken every 2 h from 0900 to 0900 h the next day for assay of plasma glucose and PGE2 and PGF2 alpha concentrations. FBMs were recorded throughout the 24 h. The mean fetal plasma glucose concentrations of the once-daily and multifed groups were not different, but there was a significant difference between the two groups in the 24-h pattern of fetal glucose concentrations. In the once-daily fed group, plasma glucose concentrations reached a peak 8 h after maternal feeding and then declined, whereas in the multifed group, fetal plasma glucose concentrations reached a plateau and were constant from 1300 to 0900 h the next day. Fetal plasma PGE2 and PGF2 alpha concentrations did not show a significant change with time of day in either group. There was a significant diurnal variation in the incidence and amplitude of FBMs in each of the two feeding groups, and the 24-h pattern of FBMs did not differ significantly between groups. Therefore it would appear that the diurnal variation of FBMs is not a consequence of the maternal feeding regimen or diurnal changes in plasma glucose or PG concentrations.     

A lack of predatory interaction between rumen ciliate protozoa and Shiga-toxin producing Escherichia coli

AIMS: To investigate interactions between rumen protozoa and Shiga toxin-producing Escherichia coli (STEC) and to ascertain whether it is likely that rumen protozoa act as ruminant hosts for STEC. METHODS AND RESULTS: The presence of stx genes in different microbial fractions recovered from cattle and sheep rumen contents and faeces was examined using PCR. In animals shedding faecal STEC, stx genes were not detected in the rumen bacterial or rumen protozoal fractions. Direct interactions between ruminal protozoa and STEC were investigated by in vitro co-incubation. Rumen protozoa did not appear to ingest STEC, a STEC lysogen or non-STEC E. coli populations when co-incubated. CONCLUSIONS: The ruminal environment is unlikely to be a preferred habitat for STEC. Bacterial grazing by rumen protozoa appears to have little, if any, effect on STEC populations. SIGNIFICANCE AND IMPACT OF THE STUDY: This study indicates that ruminal protozoa are unlikely to be a major factor in the survival of STEC in ruminants. They appear as neither a host that protects STEC from the ruminal environment nor a predator that might reduce STEC numbers.     

Effect of the tropical forage calliandra on microbial protein synthesis and ecology in the rumen

C.S. MCSWEENEY, B. PALMER, R. BUNCH AND D.O. KRAUSE. 2001 .
Aims: To determine the effect of condensed tannins in Calliandra calothyrsus (calliandra) on rumen microbial function.
Methods and Results: Microbial populations, ruminal protein synthesis and fermentation end-products were measured in sheep fed roughage hay supplemented with calliandra (30%), with and without inclusions of polyethylene glycol (PEG) to counteract the effect of tannin. Molecular and conventional enumeration techniques were used to quantify rumen bacteria, fungi and protozoa, and protein synthesis was predicted from estimates of urinary purine excretion. The total number of cellulolytic bacteria, including populations of Fibrobacter succinogenes and Ruminococcus spp., was significantly lower in sheep supplemented with calliandra and these populations increased when animals were treated with PEG. By contrast, protozoa and fungi and the microbial group containing Bacteroides - Porphyromonas - Prevotella bacteria appeared to be less affected. The efficiency of microbial protein synthesis in the rumen was not altered significantly.
Conclusions: Calliandra caused significant shifts in rumen microbial populations without changing the efficiency of protein synthesis.
Significance and Impact of the Study: The effect of calliandra tannins on rumen digestion may result more from complexing with nutrients than direct inhibition of micro-organisms.     

Sulphate recycling and metabolism in sheep and cattle.

Merino wethers and Brahman x Shorthorn steers, offered lucerne or spear grass hay, were used to study the movements of sulphate through pools in plasma and ruminal liquor. The irreversible loss of sulphate from ruminal liquor was 60 and 76% of sulphur ingested for both species fed lucerne and spear grass respectively. The irreversible loss of sulphate from the plasma averaged 67 and 56% of sulphur ingested for animals fed lucerne and spear grass respectively. Daily recycling of sulphate to the rumen of sheep was 98 mg sulphur on the lucerne diet and 3.9 mg sulphur on the spear grass diet. Sulphate recycling in cattle fed lucerne was 533 mg sulphur; in cattle fed spear grass the value was 234 mg sulphur. Over 6 days following an intravenous injection of [35S]sulphate into sheep and cattle fed lucerne, 5-10% of the dose was excreted in the faeces and c. 10% was retained. Corresponding values for animals fed spear grass were 23-31% in faeces and 40-51% of the dose retained. After intraruminal injections of [35S]sulphate, animals fed lucerne excreted 15-18% of the dose in the faeces and retained 25-30% of the dose over 6 days. Values for animals fed spear grass were 22-26% in faeces and 62-70% retained. It was concluded that sulphate recycling to the rumen is a limiting factor in microbial synthesis for sheep fed low-quality roughage, and that secretion of endogenous sulphur into the postruminal tract of ruminants is of importance in the metabolism of sulphate.     

A simulation model “CTR Dairy” to predict the supply of nutrients in dairy cows managed under discontinuous feeding patterns

A simulation rumen model has been developed to function under non-steady state conditions in order to allow prediction of nutrient availability in dairy cows managed under discontinuous feeding systems. The model simulates availability of glycogenic, aminogenic and lipogenic nutrients to lactating dairy cows fed discontinuously. The model structure considers input of up to three different feeds fed independently at any time during the day. Feeds are described by their nitrogen (N), carbohydrate and fatty acid fractions. The N containing feed fractions include ruminally undegraded crude protein (CP), ruminally insoluble but potentially degradable CP, ruminally soluble CP and ammonia N. The feed carbohydrate fractions include ruminally undegradable neutral detergent fibre (NDF), ruminally degradable NDF, ruminally insoluble starch, ruminally soluble starch and sugars. The fatty acids in the feeds are divided between long chain fatty acids and volatile fatty acids (VFA). Additionally four pools were defined representing absorption of amino acids, glucose, long chain fatty acids and volatile fatty acids. The rumen microbial population is represented as a single pool. Besides a flexible structure, new features to the extant model include adoption of the concept of chewing efficiency (or chewing effectiveness) during eating, variable fractional ruminal absorption rates of VFA and variable fractional ruminal degradation rates of NDF as a function of rumen liquid pH, as well as a variable rumen volume which directly affects rumen concentrations of metabolites. The model continuously (i.e., by minute) predicts release of soluble components from the feeds in the rumen, concentration and absorption of fermentation end products in the rumen, rumen pools of nutrients and microbial biomass dynamics, as well as passage of microbial biomass and non-fermented nutrients from the rumen, in response to various feeding strategies. Model evaluation covered a wide range of feeding strategies that included pasture and housed feeding systems. Overall, the mean square prediction error (MSPE) as a percentage of the observed mean was relatively low (<10%) with a high amount of the total variation explained by random variation (>65%). Deviation from unity varied between 23% (rumen dry matter content) and 25% (NDF), indicating some consistent over and/or under prediction. A more detailed evaluation was done based on studies available that reported diurnal behaviour of key model outputs such as rumen pools, rumen pH, and rumen VFA. The predictions broadly simulated the observed values quantitatively, relative to general diurnal patterns, and relative to differences between treatments in the predicted diurnal patterns. Results show that the model provides a tool to assess potential outcomes of changing feeding strategies which may be particularly valuable in assessing selection of feeds, amounts and times of the day to offer the feeds. The continuous nature of the simulated output also allows determination of the time(s) of the day that ruminal (and/or post-ruminal) delivery of nutrients may limit ruminal output of nutrients (and/or availability of nutrients) to support milk nutrient synthesis.     

Influence of several feeds on bacteria in sheep and goat rumen liquor in vitro

Bacteriological studies were made with in vitro sheep and goat ruminal fluids supplemented with several feeds (alfalfa hay, wheat straw, Agave americana, Opuntia ficus indica and Atriplex nummularia) during anaerobic incubation at 38-39 degrees C. Drastic changes in the bacterial population of sheep ruminal fluids occurred in the presence of different feeds, particularly with addition of feeds of low nutritional quality (wheat straw, A. americana and O. ficus indica). However, the bacterial population in goat rumen liquor was little affected by the addition of the same feeds. These results, which suggest that the rumen bacteria in goats are less affected by different nutritional conditions than the rumen bacteria in sheep, are discussed.     

Rumen Microbial Ecology in Mule Deer

Mule deer rumen microbial populations from animals in the natural habitat in Utah and from captive deer fed various rations were studied. The microorganisms were characterized on the basis of morphology and Gram reaction. Rumen samples contained 13 identifiable types of bacteria and one genus of ciliate protozoa (Entodinium). Highest rumen bacterial populations were produced on rations containing barley. No differences in proportions of ruminal bacteria in the various morphological groups could be detected when animals were fed either natural browse plants or alfalfa hay. The total numbers of bacteria were similar for animals feeding on controlled diets of browse or hay and those in the natural habitat. Numbers of some bacterial types were directly related to ciliate protozoal numbers, whereas others were inversely related. Highest rumen ciliate protozoal populations were observed on rations containing barley. No differences in protozoal populations were noted between diets containing only browse or hay. Seasonal variations were noted in ciliate protozoal numbers from deer feeding in the natural habitat. The total number of ciliate protozoa decreased in the fall and winter and remained low until spring. There were indications that salt in the deer diet favorably affected rumen ciliate protozoa. Rather than revealing direct deer management applications, this study serves to stimulate and illuminate new approaches to research in range and wildlife nutrition.