Amino acid flux in ruminal and gastric veins of sheep: effects of ruminal and omasal injections of free amino acids and carnosine

The possibility of free amino acid (FAA) and peptide absorption across the ruminant stomach wall was studied in multicatheterized wethers fed every 12 h. During the last third of the feeding cycle, two intraruminal or intraomasal injections of solutions containing increasing amounts of Ser, Gly, Val, Met, Phe, Lys, and carnosine were successively performed. Before injections, a net uptake of each of these FAA was measured in the ruminal and the gastric veins. The ruminal injections produced a linear increase in ruminal FAA concentration. The highest ruminal concentrations (observed with 3 g of FAA and carnosine) ranged between 5 and 14 mM. After ruminal injections, Ser (P < .05), Gly (P < .05), Val (P < .05), Met (P < .10), and Lys (P < .10) uptake decreased and carnosine net release linearly increased (P < .05), suggesting absorption across the ruminal epithelium. Owing to the low net flux generated by high ruminal concentration, the ruminal epithelium permeability to these molecules seemed to be low. After omasal injections, net flux of injected FAA were not modified, suggesting a low permeability of the gastric epithelia to FAA. Carnosine net release linearily increased (P < .05) with increasing level of carnosine injection, indicating the possibility of dipeptide absorption at the gastric level. This study demonstrated in vivo that the stomach epithelia possess the capacity to absorb FAA and small peptides; however, the permeability of these epithelia to these molecules seemed limited.     

日粮补充异丁酸对犊牛生长性能、瘤胃发酵和纤维分解菌菌群的影响

为探索异丁酸对犊牛生长性能、瘤胃发酵、纤维分解菌菌群和酶活性的影响,试验选用15日龄荷斯坦犊牛36头,随机分成4组,对照组、低水平异丁酸组(LIB)、中水平异丁酸组(MIB)和高水平异丁酸组(HIB)分别饲喂异丁酸0、3、6和9g·d^-1,预饲15d,分别于60日龄(断奶)和90日龄测定体重和采集瘤胃液进行分析。结果表明,MIB组和HIB组犊牛干物质采食量、日增重和经济效益显著高于对照组(P<0.05)。90日龄时HIB组犊牛瘤胃pH值显著低于对照组和LIB组(P<0.05)。MIB和HIB组瘤胃总挥发性脂肪酸和乙酸浓度显著高于对照组和LIB组(P<0.05);MIB和HIB组犊牛60日龄时瘤胃乙酸/丙酸显著高于对照组(P<0.05),90日龄时显著高于对照组和LIB组(P<0.05)。60和90日龄时MIB和HIB组瘤胃异丁酸均显著高于对照组(P<0.05)。60日龄时MIB和HIB组木聚糖酶和α-淀粉酶显著高于对照组(P<0.05),MIB和HIB组纤维二糖酶、果胶酶、溶纤维丁酸弧菌、黄色瘤胃球菌和产琥珀酸丝状杆菌显著高于对照组和LIB组(P<0.05);90日龄时MIB和HIB组各种瘤胃酶活力和纤维分解菌均显著高于对照组和LIB组(P<0.05)。结果显示,日粮补充异丁酸促进了犊牛瘤胃纤维素分解菌的生长,提高了纤维素分解酶的活性,进而促进了犊牛瘤胃发酵和生长发育。由于MIB与HIB之间各指标差异不显著,兼顾经济效益,在本试验条件下异丁酸的最佳添加量为6.0g·d^-1。     

Effects of laidlomycin propionate and monensin on the in vitro mixed ruminal microorganism fermentation.

The objective of this study was to compare the effects of laidlomycin propionate and monensin on the in vitro fermentation of ground corn, Trypticase, or alfalfa hay by mixed ruminal microorganisms. Ruminal fluid was collected from two steers fed 9.27 kg DM of a high-concentrate (62.2% ground corn and 17.4% cottonseed hulls) diet per day and composited. In the first study, no ionophore was included in the diet; the diet in the second study contained 11.1 g of laidlomycin propionate per ton of feed. The animals were allowed an adjustment period of 14 d for each dietary treatment before samples were collected. When ruminal fluid from unadapted animals was used, both monensin and laidlomycin propionate decreased (P<.05) CH4 concentration and the acetate:propionate ratio with ground corn and alfalfa hay. Monensin reduced (P<.05) in vitro dry matter disappearance of alfalfa and increased (P<.05) final pH in the ground corn and alfalfa hay fermentations. Both laidlomycin propionate and monensin decreased (P<.05) concentrations of acetate, propionate, isobutyrate, isovalerate, CH4, and NH3 in Trypticase fermentations. When ruminal fluid from adapted animals was used, both ionophores still reduced the concentrations of most fermentation products. However, there was generally less inhibition compared with fermentations inoculated with unadapted mixed ruminal microorganisms. In the presence of 5 mM maltose, mixed ruminal bacteria produced high concentrations (10 to 11 mM) of lactate, and addition of both ionophores to these fermentations was effective in reducing (P<.05) lactate production. In conclusion, laidlomycin propionate alters the mixed ruminal microorganism fermentation in a manner similar to monensin, but, at the concentrations used in this study, monensin seemed to be a more potent inhibitor.     

Effects of additives on in vitro ruminal fermentation: a comparison of monensin and bacitracin, another gram-positive antibiotic

Mixed ruminal bacteria (n = 4) were incubated in anaerobic media for 24 h in vitro with either hay, corn meal, protein hydrolyzate or hydrogen gas as the substrate. The ionophore monensin and the polypeptide antibiotic bacitracin were added to the incubation flasks at concentrations ranging from 0 to 10 or 40 mg/liter. As was expected, monensin decreased methane production, increased the ratio of propionate to acetate and decreased the deamination of amino acids. Monensin had little effect on methane production, however, if hydrogen gas was the fermentation substrate. Bacitracin, another gram-positive antibiotic with a distinctly different cellular target, was somewhat less potent than monensin, but it produced strikingly similar responses. This similarity of fermentation patterns suggested that monensin action in the rumen is probably due to its activity as a gram-positive antibiotic, and that any gram-positive antibiotic not suppressed by resistance may produce fermentation effects similar to those of monensin. The cellular action of monensin as an ionophore in membranes is probably little more than a means of inhibiting sensitive species. Many gram-positive antibiotics have little affect on ciliate protozoa or coccidia.     

Effects of monensin on monovalent ion metabolism and tissue concentrations in lambs

A study consisting of two trials was conducted to determine the effects of monensin on the apparent absorption and retention of sodium (Na) and potassium (K) and to examine changes in tissue and ruminal fluid concentrations of these minerals in lambs. Eight lambs (39 kg) were used in trial 1 and 10 lambs (37 kg) were used in trial 2. Animals were used in randomized block designs, blocked by weight, and fed a high concentrate diet with or without 20 mg/kg monensin. Trials began with a dietary adjustment period lasting 18 d in trial 1 and 21 d in trial 2. Animals were then placed in metabolism stalls for a 10-d stall adjustment period followed by a 12-d collection period. Collections for mineral balance were made during the first 10 d of the collection period. Blood and ruminal fluid samples were obtained on d 11 of the collection period. Lambs were slaughtered on d 12 of the collection period and tissue samples were collected. Sodium retention decreased (P less than .05) 86.2% when monensin was fed. Apparent K absorption increased (P less than .05) 16.7%, while K retention increased (P less than .10) 52.6% when monensin was fed. In lambs fed monensin, ileal Na decreased (P less than .10) 13.8%. These results indicate that dietary monensin alters the metabolism of Na and K in lambs.     

Salinomycin and lasalocid effects on growth rate, mineral metabolism and ruminal fermentation in steers

Two experiments were conducted to determine the effects of salinomycin and lasalocid on metabolism and growth of growing steers. In Exp. 1, 80 Angus steers (228 kg) were assigned to the following treatments: 1) control, 2) 50 mg salinomycin.hd-1.d-1, 3) 100 mg salinomycin.hd-1.d-1 and 4) 250 mg lasalocid.hd-1.d-1. Steers were fed corn silage once daily with allotments based on the amount of silage that each pen of five steers would consume in a 24-h period. In addition, .81 kg/hd of a corn-soybean meal supplement was fed daily during the 112-d study. Daily gains were similar across treatments, but feed intake was lower (P less than .05) for steers fed ionophores. Molar proportions of ruminal acetate were lower (P less than .05) in steers fed ionophores at 28 and 90 d. Ruminal propionate was lower (P less than .05) in control steers at 28 d, but values were similar across treatments on d 90. Plasma copper (Cu) was lower (P less than .05) in control steers on both sampling days. In Exp. 2, 16 Hereford steers were allotted to two blocks of eight animals each and assigned to one of three treatments: 1) control (n = 6), 2) 11 mg salinomycin/kg diet (n = 6) and 3) 33 mg lasalocid/kg diet (n = 4). Following a 28-d adjustment period, apparent absorption and retention of macrominerals and nitrogen (N) were determined during a 5-d collection period. Apparent absorption and retention of N did not differ among treatments when data were analyzed using N intake as a covariate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in ruminal concentrations of microbial ammonia and amino acids due to monensin and time

The effect of monensin (33 mg/kg) and no monensin on distribution of ammonia and free amino acids in fluid and particulate phases of ruminal contents was studied. Two Jersey cows and two Angus-Hereford steers, weighing approximately 350 kg and each containing a ruminal cannula were meal fed a 65% concentrate diet for two periods. Feed was available for 30 min; any feed not eaten was removed after this time. Whole ruminal contents were sampled before feeding, immediately after feed removal and 1, 2, 3, 4, 6, 8, 10 and 12 h after feed removal. A crossover design with split-plot in time was used with four observations per time point per treatment. Extracellular (E) ammonia and amino acids were determined on high speed supernatants of strained ruminal fluid. Total (T) ammonia and amino acids were obtained by lysing microbial cells with 1% cetyltrimethylammonium bromide (CTAB) and one freeze treatment before centrifugation. Intracellular (I) amino acids and ammonia were determined as T minus E. Squeezed particles were suspended in .1 N HCl containing 1% CTAB. Total and E ammonia were higher throughout the study for no monensin vs monensin (P less than .05). Intracellular ammonia was low (.03 to 1 mM) and did not change (P greater than .10) across time for either dietary treatment. Intracellular amino acids ranged from 1.2 to 4.5 mM and were higher (P less than .05) than E amino acids (.9 to 2.2 mM) for both diets immediately after feeding. Monensin did not significantly lower (P greater than .10) T amino acids compared with no monensin throughout sampling (2.6 and 3.1 mM, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of a monensin ruminal delivery device on daily gain, forage intake and ruminal fermentation of steers grazing irrigated winter wheat pasture

Two trials evaluated the effects of a monensin ruminal delivery device (MRDD) on steers grazing winter wheat pasture. In Trial 1, 60 Hereford steers (initial wt 238.5 kg) grazed a 21.9-ha paddock of Vona-variety winter wheat for 112 d. Steers were assigned to either MRDD or control (C) treatments in a randomized complete block design. In Trial 2, eight ruminally cannulated steers (avg wt 234.4 kg) grazed a 2.4-ha paddock of Vona-variety wheat and were assigned randomly to either MRDD or C treatments. Three 11-d collection periods were conducted during early February, early March and early April. Chromic oxide was dosed to determine fecal output, and ruminal samples were collected on d 6 of each period. Nylon bags containing ground wheat forage were incubated ruminally beginning on d 8. In Trial 1, steers with MRDD tended (P less than .11) to gain more weight than C steers (.44 vs .38 kg/d). In Trial 2, wheat forage intake, in situ DM disappearance, ruminal pH, ruminal ammonia concentrations and ruminal proportions of acetate and total VFA concentrations were not affected by treatment. Ruminal proportions of propionate were increased (P less than .05) slightly by MRDD (20.3 and 19.2 mol/100 mol for MRDD and C, respectively). Butyrate proportions in ruminal samples were decreased (P less than .05) by MRDD during March but not in other sampling periods. Ruminal fluid chlorophyll concentration was less (P less than .05) for MRDD-treated vs C steers during early March but was greater (P less than .10) for MRDD-treated steers during early April. The MRDD shows promise as a method of supplying monensin to cattle grazing winter wheat forage.     

Effect of increasing ruminal butyrate on portal and hepatic nutrient flux in steers.

Six Holstein steers (mean +/- SE BW = 344 +/- 10 kg) fitted with hepatic, portal, and mesenteric vein and mesenteric artery catheters and a ruminal cannula were used in a 6 x 6 Latin square design to evaluate the effects of increasing ruminal butyrate on net portal-drained visceral and hepatic nutrient flux. Steers were fed a 40% brome hay, 60% concentrate diet in 12 portions daily at 1.25 x NEm. Water (control) or butyrate at 50, 100, 150, 200, or 250 mmol/h was supplied continuously via the ruminal cannula. Simultaneous arterial, portal, and hepatic blood samples were taken at hourly intervals from 15 to 20 h of ruminal infusion. Portal and hepatic blood flow was determined by continuous infusion of P-aminohippurate, and net nutrient flux was calculated as the difference between venous and arterial concentrations times blood flow. Ruminal and arterial concentrations and total splanchnic flux of butyrate increased (P less than .01) with increased butyrate infusion. Arterial concentrations of acetate (P less than .10), alpha-amino-N (P less than .05), and glucose (P less than .01) decreased with increased butyrate, whereas arterial beta-hydroxybutyrate (P less than .01) and acetoacetate (P less than .05) increased. Increased butyrate produced an increased portal-drained visceral flux of acetoacetate and an increased net hepatic flux of beta-hydroxybutyrate. Urea N and glucose net portal and hepatic fluxes were not affected by ruminal butyrate. Alpha-amino-N uptake by the liver decreased with increased butyrate (P less than .10). Simple linear regression (r2 = .985) indicated that 25.8% of ruminally infused butyrate appeared in portal blood as butyrate. Only 14% could be accounted for as net portal-drained visceral flux of acetoacetate plus beta-hydroxybutyrate.     

Effects of monensin on voluntary intake, eating and ruminating behavior and ruminal motility in heifers fed corn silage

Eating and ruminating behavior and associated ruminal motility of six heifers (1/4 Brahman X 1/4 Jersey X 1/2 Angus, 290 kg average weight) given ad libitum access to corn silage with or without 100 mg monensin X head-1 X d-1 were examined according to a two-period crossover design. There was no effect (P greater than .05) of monensin on level of intake, daily and unitary eating, ruminating and masticating times [min X g dry matter-1 X (kg body weight X 75)-1], duration or number of these activity periods, duration of main meals or latency time for onset of rumination following cessation of main eating activities. With the monensin treatment, daily numbers of normal boli and total boli were decreased (P less than .05) and mean duration of one rumination bolus cycle was longer (P less than .05). Analysis of covariance indicated relationships between intake of corn silage and duration of the main morning meal, duration or number of rumination boli and total ruminal contractions were affected (P less than .01) by monensin. Frequency and unitary number of strong cranio-dorsal ruminal contractions were similar for both treatments. During eating, number of contractions per minute was about twice (2.55/min) that during idling and rumination activity (1.43/min and 1.22/min, respectively). The unitary daily number of contractions was negatively (P less than .05) related to level of intake. Total daily ruminal contractions were slightly reduced (-3.96%, P greater than .05) by monensin. Results are interpreted to suggest that monensin indirectly affects rumination through a lowered motility and thereby affects turnover, gut fill and intake.     

A meta-analysis of fumarate effects on methane production in ruminal batch cultures

The objective of this study was to understand the effects of fumarate addition on methane (CH4) and VFA production in the rumen through a meta-analysis of its effects on ruminal batch cultures. Because the reduction of fumarate to succinate can draw electrons away from ruminal methanogenesis, fumarate has been studied as a potential feed additive to decrease CH4 production in ruminants. The average decrease in CH4 in batch cultures was of 0.037 micromol/micromol of added fumarate, which is considerably lower than 0.25 micromol/micromol, the decrease predicted from the stoichiometry of the reactions involved. One reason that fumarate was not effective at decreasing CH4 in batch cultures was that only an average of 48% of added fumarate appeared to be converted to propionate. Secondly, the incorporation of reducing equivalents in the conversion of fumarate to propionate was almost entirely offset by their release from an average of 20% of added fumarate that appeared to be converted to acetate. Thermodynamic calculations indicated that the conversion of added fumarate to both propionate and acetate was feasible. Fumarate appears to be more effective in decreasing CH4 production and increasing propionate in continuous culture than in batch culture. This suggests that microbial adaptation to fumarate metabolism can be important. Variation in populations of fumarate-reducers, methanogens, and protozoa could all be involved. Fumarate supplementation for an extended period may result in the amplification of otherwise small populations of fumarate-reducers. Addition of some of these organisms may be helpful to improve fumarate conversion to propionate. Strategies based on enhancing the rumen's capacity to convert fumarate to propionate by maintaining a low fumarate concentration have been effective. Thermodynamic considerations should be taken into account when designing strategies for CH4 abatement through the addition of external electron acceptors.     

Effects of feeding polyclonal antibody preparations on ruminal bacterial populations and ruminal pH of steers fed high-grain diets

Three experiments with factorial arrangements of treatments were designed to test the efficacy of avian-derived polyclonal antibody preparations (PAP) against Streptococcus bovis (PAP-Sb) or Fusobacterium necrophorum (PAP-Fn) in reducing ruminal counts of target bacteria in beef steers supplemented or not with feed additives (300 mg of monensin/d and 90 mg of tylosin/d; MT). Feeding increasing doses of PAP-Sb in Exp. 1 or a single dose in Exp. 2 reduced S. bovis counts in a cubic fashion (P = 0.014). In Exp. 1 and 2, inclusion of MT in the diet had no effect (P > 0.05) on ruminal S. bovis counts. In Exp. 2, ruminal pH was increased (P < 0.05) by feeding PAP-Sb, MT, and PAP-Sb plus MT. Ruminal F. necrophorum counts were reduced by feeding PAP-Fn (P = 0.002) and MT (P < 0.001). Reduction in ruminal F. necrophorum counts was greater (P = 0.008) when feeding MT alone than when feeding PAP-Fn and MT together. In Exp. 3, ruminal S. bovis counts were not affected (P = 0.64) by PAP-Fn. Ruminal pH was not affected (P = 0.61) by feeding PAP-Fn, and the total anaerobic bacterial count was not affected (P > 0.05) by either PAP-Sb or PAP-Fn in Exp. 1 or Exp. 3. In conclusion, PAP of avian origin and against S. bovis or F. necrophorum were effective in reducing target ruminal bacterial populations. These PAP could be effective in preventing the deleterious effects associated with these bacteria, and possibly in enhancing animal performance.     

In vitro bacterial growth and in vivo ruminal microbiota populations associated with bloat in steers grazing wheat forage

The role of ruminal bacteria in the frothy bloat complex common to cattle grazing winter wheat has not been previously determined. Two experiments, one in vitro and another in vivo, were designed to elucidate the effects of fresh wheat forage on bacterial growth, biofilm complexes, rumen fermentation end products, rumen bacterial diversity, and bloat potential. In Exp. 1, 6 strains of ruminal bacteria (Streptococcus bovis strain 26, Prevotella ruminicola strain 23, Eubacterium ruminantium B1C23, Ruminococcus albus SY3, Fibrobacter succinogenes ssp. S85, and Ruminococcus flavefaciens C94) were used in vitro to determine the effect of soluble plant protein from winter wheat forage on specific bacterial growth rate, biofilm complexes, VFA, and ruminal H2 and CH4 in mono or coculture with Methanobrevibacter smithii. The specific growth rate in plant protein medium containing soluble plant protein (3.27% nitrogen) was measured during a 24-h incubation at 39 degrees C in Hungate tubes under a CO2 gas phase. A monoculture of M. smithii was grown similarly, except under H2:CO2 (1:1), in a basal methanogen growth medium supplemented likewise with soluble plant protein. In Exp. 2, 6 ruminally cannulated steers grazing wheat forage were used to evaluate the influence of bloat on the production of biofilm complexes, ruminal microbial biodiversity patterns, and ruminal fluid protein fractions. In Exp. 1, cultures of R. albus (P < 0.01) and R. flavefaciens (P < 0.05) produced the most H2 among strains and resulted in greater (P < 0.01) CH4 production when cocultured with M. smithii than other coculture combinations. Cultures of S. bovis and E. ruminantium + M. smithii produced the most biofilm mass among strains. In Exp. 2, when diets changed from bermudagrass hay to wheat forage, biofilm production increased (P < 0.01). Biofilm production, concentrations of whole ruminal content (P < 0.01), and cheesecloth filtrate protein fractions (P < 0.05) in the ruminal fluid were greater on d 50 for bloated than for nonbloated steers when grazing wheat forage. The molecular analysis of the 16S rDNA showed that 2 different ruminal microbiota populations developed between bloated and nonbloated animals grazing wheat forage. Bloat in cattle grazing wheat pastures may be caused by increased production of biofilm, resulting from a diet-influenced switch in the rumen bacterial population.     

牛膝多糖的作用机制及对动物模型的影响

牛膝多糖(ABPS)是一种水溶性的生物活性多糖,在体内发挥着极其重要的生理功能,可参与机体的免疫调节,并具有抗病毒、抗肿瘤和抗氧化等生物学作用。本文主要从ABPS的理化性质、结构、作用机制及对动物模型的影响等方面进行了综述。     

Effects of dietary monensin and sodium propionate on net nutrient flux in steers fed a high-concentrate diet

Four Holstein steers (mean body weight, 211 +/- 20 kg) were utilized in a Latin-square design with a 2 X 2 factorial arrangement of treatments to investigate the effects of monensin (0 or 220 mg/d) and sodium propionate (0 or 450 g/d) on net nutrient flux. Steers were surgically prepared with hepatic portal and mesenteric venous catheters and an elevated carotid artery, after which they were adjusted to their basal diet (85% concentrate) and initial treatment over 19 d. Samples of arterial and portal venous blood were taken hourly over 3 h for the final 3 d of each 2-wk period. Portal blood flow was determined by primed continuous infusion of para-aminohippurate. No changes were seen in dry matter intake, portal blood flow, or net portal flux of any of the volatile fatty acids with the exception of butyrate flux, which decreased with monensin addition. Addition of monensin decreased net portal flux of ammonia, decreased recycling of urea, and tended to increase the net portal flux of glucose. Addition of sodium propionate increased the net portal flux of glucose and decreased the net portal flux of alpha-amino-N. These results are interpreted to suggest that changes in the products of ruminal fermentation may not be exactly translated into the products appearing in the portal circulation, and more information is needed to describe these relationships.     

Effect of growth promoters on monensin toxicity in broiler chicks 1

1. An experiment was carried out with male broiler chicks to evaluate the combined effect of monensin (150 mg/kg) and the growth promoters (GPs) Zn bacitracin (BAC, 50 mg/kg), virginiamycim (VIR, 25 mg/kg) and avoparcin (AVO, 20 mg/kg) fed from 7 to 28 d of age on performance, utilisation of dietary nutrients, yield of defeathered eviscerated carcases (DEC) and size of various organs. The effect of the GPs in the monensin‐unsupplemented diets fed up to 49 d of age on performance and carcase was also determined.

2. Monensin significantly (P < 0.05) depressed food intake, weight gain and food efficiency from 7 to 28 d of age. None of the GPs was able to counteract these effects. However, AVO slightly ameliorated them. AVO also significantly increased food intake and improved gain and food efficiency during 7 to 28, but not 28 to 49 or 7 to 49 d of age. VIR and BAC did not affect performance in either age period.

3. Monensin did not affect the utilisation of dietary dry matter, fat or energy, but it significantly decreased nitrogen utilisation. AVO improved nitrogen and fat utilisation and increased dietary AME_n content. AME_n was also increased by VIR. The utilisation of these nutrients was not affected by the interactions between monensin and the GPs.

4. Monensin did not affect yield of the DEC or the relative liver size at 31 d of age. It significantly increased the relative length of the small intestine (SI) and decreased its specific weight. AVO significantly increased yield at 31, but not at 53 d of age. BAC and VIR did not affect this variable. AVO and VIR, but not BAC, at both age periods reduced, at times significantly, the size, length and specific weight of the SI.

5. Our conclusions: BAC, VIR and AVO do not counteract the toxic effect of monensin. The effect of GPs in improving performance decreases and even disappears with age, while their effect in reducing the size of the SI is still evident in 49‐d‐old birds.     

Effects of dietary concentrate level and chromium-methionine supplementation on ruminal fermentation,and ruminal bacterial and fatty acid composition in Tan lambs北大核心CSCD

This study evaluated the effects of dietary concentrate level and chromium methionine(Cr-Met)supplementation on ruminal fermentation and fatty acid composition, and ruminal bacteria abundance in Tan lambs. Forty male Tan lambs [(21.00±1.23) kg body weight, 5 months of age] were randomly assigned to four treatment groups with 10 lambs in each treatment. The treatments were: a low-concentrate (LC) diet (concentrate:forage, 35:65) without Cr-Met supplementation; a high-concentrate (HC) diet (concentrate:forage, 55:45) without Cr-Met supplementation; groups fed the HC diet with 0.75 or 1.50 g·d-1·lamb-1 Cr-Met (HCM and HCH, respectively). Ruminal fluid was collected on day 65 with an oral stomach tube about 3 h after the morning feed and samples used for fermentation analysis, fatty acid composition determination and bacterial DNA extraction. It was found that: 1) Ruminal pH, acetate proportion and acetate:propionate were greater (P<0.05) with the LC diet whereas microbial crude protein, propionate and valerate proportions were greater (P<0.05) with the HC diet. The acetate:propionate was greater (P<0.05) in the HCM group than in the HC group. 2) For the HC diet, the DNA abundances of Butyrivibrio fibrisolvens vaccenic acid subgroup (Butyrivibrio VA) and Ruminococcus flavefaciens were decreased (P<0.05), compared with the LC diet, whereas the DNA abundance of Anaerovibrio lipolytica was increased (P<0.05). For lambs fed the HC diet, DNA abundances of B. fibrisolvens stearic acid subgroup, Butyrivibrio VA, Butyrivibrio proteoclasticus, and A. lipolytica showed a linear decrease (P<0.05) with increasing Cr-Met supplementation level; However, the DNA abundance of R. flavefaciens showed a linear increase (P<0.05). 3) Compared with the LC group, the concentrations of t11 C18:1, trans C18:1, c9t11 CLA, t10c12 CLA, C18:2n6, and C18:3n3 were decreased by the HC diet without Cr-Met supplementation whereas the concentration of C18:0 was increased. There was a linear increase in t11 C18:1 and trans C18:1 with increasing Cr-Met supplementation level in lambs fed the HC diet. The results suggest that the HC diet inhibited the growth of ruminal bacteria involved in the ruminal biohydrogenation process, and the addition of Cr-Met had a potentially positive effect on conjugated linoleic acid (CLA) synthesis in body tissue. © 2022, Editorial Office of Acta Prataculturae Sinica. All rights reserved.