Comparison of rumen bacteria distribution in original rumen digesta,rumen liquid and solid fractions in lactating Holstein cows

Background: Original rumen digesta, rumen liquid and solid fractions have been frequently used to assess the rumen bacterial community. However, bacterial profiles in rumen original digesta, liquid and solid fractions vary from each other and need to be better established.Methods: To compare bacterial profiles in each fraction, samples of rumen digesta from six cows fed either a high fiber diet(HFD) or a high energy diet(HED) were collected via rumen fistulas. Rumen digesta was then squeezed through four layers of cheesecloth to separate liquid and solid fractions. The bacterial profiles of rumen original digesta, liquid and solid fractions were analyzed with High-throughput sequencing technique.Results: Rumen bacterial diversity was mainly affected by diet and individual cow(P 0.05) rather than rumen fraction. Bias distributed bacteria were observed in solid and liquid fractions of rumen content using Venn diagram and LEf Se analysis. Fifteen out of 16 detected biomarkers(using LEf Se analysis) were found in liquid fraction, and these 15 biomarkers contributed the most to the bacterial differences among rumen content fractions.Conclusions: Similar results were found when using samples of original rumen digesta, rumen liquid or solid fractions to assess diversity of rumen bacteria; however, more attention should be draw onto bias distributed bacteria in different ruminal fractions, especially when liquid fraction has been used as a representative sample for rumen bacterial study.     

Comparative characterization of reticular and duodenal digesta and possibilities of estimating microbial outflow from the rumen based on reticular sampling in dairy cows

The objective of this experiment was to investigate the possibility of estimating the outflow of nutrients and microbial protein from the rumen based on sampling reticular contents as an alternative to duodenal sampling. Microbial protein flow estimates were also compared with a third method based on sampling of ruminal contents. Reticular and duodenal digesta and ruminal contents were recovered from 4 cows used in a 4 x 4 Latin square design experiment, in which the ruminal effects of 4 exogenous enzyme preparations were studied. Large and small particulate and fluid markers were used to estimate digesta flow in a triple-marker model; 15N was used as a microbial marker. Reticular and duodenal digesta were segregated into small and large particles (SP and LP, respectively) and a fluid phase, and ruminal digesta was segregated into particulate and fluid phases. Compared with digesta recovered at the duodenum, reticular digesta had lower OM and greater NDF contents. The proportion of microbial N was notably greater in the fluid phase of reticular digesta. Ruminal outflow of DM and OM was greater (by 17 and 28%) and that of NDF was lower (by 14%) when estimated from duodenal compared with reticular samples. There was no difference in the estimated flow of starch and nonammonia and microbial N between the reticular and duodenal techniques. Microbial N flow estimated based on ruminal sampling was similar to those based on duodenal and reticular sampling. The ruminal method, however, grossly overestimated flow of DM, OM, and NDF. This study supports the concept that microbial protein outflow from the rumen can be measured based on sampling of ruminal or reticular digesta. The reticular sampling technique can also provide reliable estimates for ruminal digestibility of OM, N, and fiber fractions. These findings need to be confirmed in experiments with basal diets varying in structure and forage-to-concentrate ratios.     

Metagenomic profiles of the rumen microbiota during the transition period in low‐yield and high‐yield dairy cows

We investigated potential relationships between rumen microbiota and milk production in dairy cows during the transition period. Twelve dairy cows were divided into a low‐yield (LY) or high‐yield (HY) group based on their milk yield. Rumen samples were taken from dairy cows at 3 weeks before parturition, and at 4, 8, and 12 weeks after parturition. 16S rDNA‐based metagenomic analysis showed that diversities of rumen microbiota in both groups were similar and the number of operational taxonomic units (OTUs) was lower in the postpartum than prepartum period in both groups. The abundance of Bacteroidetes and ratio of Bacteroidetes:Firmicutes was higher in the HY than the LY group. OTUs assigned to Prevotella bryantii, Fibrobacter succinogenes, Ruminococcus albus, Butyrivibrio fibrisolvens, and Succinivibrio sp. were abundant in the HY group. These OTUs were significantly related to the propionate molar proportion of rumen fluids in the HY group. OTUs assigned to Lachnospiraceae, Bifidobacterium sp. and Saccharofermentans were dominant in the LY group. Predictive functional profiling revealed that abundance of gene families involved in amino acid and vitamin metabolism was higher in the HY than the LY group. These results suggest that the community structure and fermentation products of rumen microbiota could be associated with milk production of dairy cows.     

Effect of heterogeneous digesta chemical composition on the accuracy of measurements of fiber flow in dairy cows.

The objective of the current study was to evaluate the effect of unrepresentative sampling of digesta particulate matter entering the omasal canal on the accuracy of fiber flow measurements. The experimental design comprised one period, one diet, and three cows as experimental units. Within each cow, the physical and chemical composition of digesta particulate matter was assessed at seven sites within the digestive tract. Three Finnish Ayshire dairy cows, equipped with ruminal and simple-T duodenal cannulas, in extended lactation were offered grass silage twice daily on an ad libitum basis. Digesta samples were collected from the rumen (dorsal and ventral sac), reticulum, omasal canal, omasum, duodenum, and rectum to determine particle size distribution in digesta, chemical composition of various particle size fractions, and distribution of two flow markers (Cr-labeled straw and indigestible NDF [INDF]) among particle size fractions. Digesta samples were wet-sieved using sieves of 2.50, 1.25, 0.630, 0.315, 0.160, and 0.080 mm. Particulate matter was analyzed for OM, NDF, and Cr concentrations, and INDF concentration was determined based on 12-d ruminal incubation. The particle size of digesta entering the omasal canal was larger compared with the omasum or the duodenum, suggesting that omasal canal samples were not representative of particle size distribution truly escaping the rumen. The concentration of potentially digestible NDF (PDNDF) decreased with decreasing particle size. The PDNDF concentration of particulate matter retained on all sieves was greatest in the rumen and gradually decreased along the digestive tract. From the reticulorumen to the omasum, the decrease was associated with decreased particle size, reflecting selective passage of particulate matter. In contrast, from the omasum to the duodenum and rectum, the PDNDF concentration decreased within each particle size fraction without effect on particle size, indicating a nonselective passage of particulate matter between these sites. Variation between particle size fractions was slightly greater for Cr concentration than for INDF concentration, indicating that unrepresentative sampling of particulate matter had a greater effect on Cr concentration compared with that of INDF. Owing to unrepresentative sampling, NDF entering the omasal canal was overestimated by 5% using INDF and underestimated by 7% using Cr as a particle phase marker. Of total NDF digestibility, proportionally 0.90, 0.07, and 0.03 occurred in the reticulorumen, omasum, and intestines, respectively. The current results indicate that, despite unrepresentative sampling of digesta particulate matter entering the omasal canal, the errors in determined NDF flow were small. The omasum may have a greater role in postruminal NDF digestion than the intestines.     

Effect of cereal straw and alfalfa hay diet on amino acid profile of gastrointestinal digesta in lactating dairy cows

This study was conducted to evaluate the effects of replacing alfalfa hay with rice straw (RS) or corn stover (CS) on amino acid (AA) profiles of gastrointestinal digesta in lactating cows. Eighteen lactating dairy cows were randomly assigned to one of three groups (n = 6) and fed identical concentrate and corn silage with different forages on dry matter basis: (i) 23% alfalfa hay and 7% Chinese wild rye hay (AH); (ii) 30% CS; and (iii) 30% RS. After the 14‐week feeding, a total of 18 cows were slaughtered to collect digesta from four representative organs, including rumen, omasum, duodenum and jejunum. The AA profiles of ruminal microbial fraction were similar among the treatments, except for greater Arg in cows fed RS than in cows fed AH or CS. Most of the analysed AA changed under different diets. Significant differences were found among the microbial fraction, rumen fluid and rumen digesta, with greater essential AA in digesta than in microbial fraction or rumen fluid and greater essential AA in microbial fraction than rumen fluid. Significant differences in individual AA profiles of digesta and relevant fluid were found across the four representative digestive tract parts, including rumen, omasum, duodenum and jejunum, showing much lower Leu proportion in CS and RS than in AH in duodenal fluid. In summary, ruminal microbes may prefer using essential AA, rather than non‐essential AA. The AA profile of ruminal microbes was constant except for Arg. The AA composition of digesta across the four digestive tracts changed dramatically, which indicated differences in the ability and efficiency of AA absorption. The lower duodenum absorbable Leu proportion in cows fed CS or RS indicated the shortage of Leu in CS or RS diets, which might also restrict the balanced AA absorption.     

Effect of dietary protein level on nitrogen metabolism in the growing bovine: II. Diffusion into and utilization of endogenous urea nitrogen in the rumen

Six Angus heifer calves (234 kg) were assigned to either a high (HP; 126.1 g N/d) or low (LP; 66.5 g N/d) protein intake to evaluate ruminal criteria associated with movement of blood urea-N (BUN)-derived NH3-N from the rumen wall into interior ruminal digesta. Calves received 4.8 kg DM/d of diets containing 30% cottonseed hulls and 70% cornsoybean meal in equal portions at 4-h intervals. Following single i.v. injections of 15N-urea, ruminal fluid was collected serially for 4 h postinjection from digesta located adjacent to the rumen wall (wall-proximate digesta; WPD) and from the center of the rumen digesta mass after manual agitation (center mixed digesta; CMD). Mean ruminal NH3-N (RAN) concentrations were higher (P less than .05) for HP than for LP, but were not affected (P greater than .05) by digesta sampling site. Ruminal urease activity was higher (P less than .05) for LP than for HP and tended (P = .14) to be higher for WPD than for CMD. Area under the 15N enrichment curve (AUC) ratios between sampling sites (WPD/CMD x 100) for RAN were greater (P less than .05) for LP than for HP. However, AUC ratios for bacterial N were not affected (P greater than .05) by protein level. Whereas BUN-derived 15NH3 appeared to thoroughly equilibrate with RAN in interior ruminal digesta with HP, there appeared to be a declining enrichment gradient for RAN from the rumen wall to the interior ruminal digesta with LP. Data are interpreted to suggest that bacteria at or near the rumen wall may preferentially utilize some BUN-derived NH3-N entering through the rumen wall in calves fed LP diets.     

Effects of soybean meal supplementation on ruminal kinetics of feed particle size reduction and passage in dairy cows fed rice straw

Six ruminal-cannulated nonlactating Holstein Friesian cows (mean body weight:660 ± 42.9 kg) were used to investigate the effect of soybean meal (SBM) supplementation on voluntary rice straw (RS) intake, feed particle size reduction, and passage kinetics in the rumen. They were allocated to two dietary treatments: RS alone or RS supplemented with SBM. Voluntary dry matter intake of RS and total tract fiber digestibility was increased by SBM supplementation (p < 0.05). Supplementation with SBM decreased rumination time per dietary dry matter (DM) and neutral detergent fiber (NDFom) intake (p < 0.01). Particle size distribution in the rumen and total ruminal NDFom digesta weights were not affected by SBM supplementation. However, the disappearance rates of total digesta and large and small particles from the rumen were increased by SBM supplementation (p < 0.01). Moreover, SBM supplementation increased the rate of size reduction in ruminal particles (p < 0.05). In situ disappearance of DM and NDFom of RS in the rumen was greater in SBM-supplemented cows than in nonsupplemented cows (p < 0.05). This study clearly showed that increased ruminal RS particle size reduction, passage, and fermentation due to SBM supplementation accelerated the RS particle clearance from the rumen and resulted in increased voluntary RS intake of dairy cows.     

Herbage intake and ruminal digestion of dairy cows grazed on perennial ryegrass pasture either in the morning or evening

This study aimed to clarify diurnal fluctuations of herbage intake, ruminal fermentation of herbage carbohydrates and proteins, and digesta particulate weight in the rumen of grazing dairy cows. Six ruminally cannulated, non‐lactating dairy cows were grazed on perennial ryegrass/white clover pasture either in the morning (04.00 to 08.00 hours) or the evening (16.00 to 20.00 hours). Cows grazed in the evening spent more time (P < 0.01) and consumed more herbage (P < 0.01) compared with cows grazed in the morning. Higher (P < 0.05) daily mean concentrations of total volatile fatty acid, propionate and n‐butyrate in rumen fluid were observed for cows grazed in the evening compared with cows grazed in the morning. Although cows grazed in the evening ingested more crude protein compared with cows grazed in the morning, no significant difference in NH₃‐N concentration in rumen fluid was observed between them. The ratio of purine‐derivative concentration to creatinine concentrations was higher (P < 0.01) in the urine of cows grazed in the evening than in cows grazed in the morning. These results clearly indicated that evening grazing was advantageous for dairy cows compared with morning grazing, in terms of ruminal fermentable energy intake and nitrogen utilization efficiency.     

Processing, mixing, and particle size reduction of forages for dairy cattle

Adequate forage amounts in both physical and chemical forms are necessary for proper ruminal function in dairy cows. Under conditions in which total amounts of forage or particle size of the forage are reduced, cows spend less time ruminating and have a decreased amount of buoyant digesta in the rumen. These factors reduce saliva production and allow ruminal pH to fall, depressing activity of cellulolytic bacteria and causing a prolonged period of low ruminal pH. Insufficient particle size of the diet decreases the ruminal acetate-to-propionate ratio and reduces ruminal pH. The mean particle size of the diet, the variation in particle size, and the amount of chemical fiber (i.e., NDF or ADF) are all nutritionally important for dairy cows. Defining amounts and physical characteristics of fiber is important in balancing dairy cattle diets. Because particle size plays such an important role in digestion and animal performance, it must be an important consideration from harvest through feeding. Forages should not be reduced in particle size beyond what is necessary to achieve minimal storage losses and what can be accommodated by existing equipment. Forage and total mixed ration (TMR) particle sizes are potentially reduced in size by all phases of harvesting, storing, taking out of storage, mixing, and delivery of feed to the dairy cow. Mixing feed causes a reduction in size of all feed particles and is directly related to TMR mixing time; field studies show that the longest particles (>27 mm) may be reduced in size by 50%. Forage and TMR particle size as fed to the cows should be periodically monitored to maintain adequate nutrition for the dairy cow.     

Effects of grass hay proportion in a corn silage‐based diet on rumen digesta kinetics and digestibility in dairy cows

In this study, we aimed to evaluate the effects of six levels of orchardgrass hay (GH) proportion (0%, 10%, 20%, 30%, 40% or 50% of dry matter) in finely chopped corn silage (CS)‐based diets on digesta kinetics of CS and GH in the rumen. Six non‐lactating, rumen‐cannulated Holstein cows were used in a 6 × 6 Latin square design. Ruminal digesta kinetics was measured by ruminal dosing of feed particle markers (dysprosium for CS, erbium for GH) followed by fecal sampling. The increase of GH proportion had a quadratic effect (P < 0.01) on total tract digestibility of neutral detergent fiber (NDF) and acid detergent fiber. The proportion of GH did not affect the particle size distribution of rumen digesta, total weight of dry matter or NDF in the rumen. The rates of large particle size reduction in the rumen for CS tended to increase linearly with increasing GH proportion (P = 0.077). A quadratic effect (P < 0.05) was found with increasing the GH proportion for the ruminal passage rate of small GH particles, but not for CS particles. The results suggested that associative effects between CS and GH could be generated on rumen digesta kinetics when cows were fed a CS‐based diet with an increased proportion of GH.     

Research note: a method for studying local differences in ruminal fermentation in dairy cattle.

A method was developed for studying local differences in ruminal fermentation. The developed sampler consisted of an acrylic glass container (460 cm3) with an aperture for digesta sampling, which could be opened and closed by the scaled "T" rod. The scale was a reference for defined rumen layers: top, middle, 5 to 10 cm and 25 to 35 cm beneath the top of particles mat, respectively, and bottom 5 to 10 cm above the rumen floor. The repeatability of the method was proved in two rumen cannulated cows. Particle/fluid ratio, pH and sample amount were measured 2 to 2 1/2 h after morning feeding in four replicates each day (over 5 days), rumen layer and animal. No significant differences between replicates were observed. The coefficients of variation (CV) of the particle/fluid ratio varied between 8.7% and 13.6%. Top layer had higher CV than middle and bottom layer. CV of pH ranged between 0.59% and 1.27%. The developed method of sampling showed satisfactory repeatability for investigation of digesta properties and fermentation in different rumen layers.     

Subacute rumen acidosis in lactating cows: an investigation in intensive Italian dairy herds

Subacute rumen acidosis (SARA) represents one of the most important metabolic disorders in intensive dairy farms that affects rumen fermentations, animal welfare, productivity and farm profitability. The aim of the present study was to study the occurrence of SARA in intensive Italian dairy herds and to determine the relationship between diet composition, ruminal pH and short chain fatty acids (SCFA) concentration. Ten commercial dairy herds were investigated; twelve cows in each herd were selected randomly among animal without clinical signs of disease, with good body condition and between 5 and 60 day-in-milk (DIM), to perform rumenocentesis and obtain rumen fluid. Ruminal pH was determined immediately after sampling and concentration of SCFA in ruminal fluid was determined on samples after storage. An other objective of this research was to study in detail the effects of rumenocentesis on animal health: this study could confirm the extreme validity of this technique as ruminal sampling. Results were subject to anova and correlation analysis using SIGMA STAT 2.03. The results indicated the presence of SARA in three herds (more than 33% cows with rumen pH < 5.5), a critical situation (more than 33% cows with rumen pH < 5.8) in five farms and a normal rumen pH condition in two herds. In particular, dairy herds show on average SCFA concentration of 150, 145, 123 mmol/l for low pH, critical pH and normal pH herds respectively. There were not significant differences among diet composition even if herds with SARA showed a light discordance between initially chemistry composition and residual feed. In the affected herds it was not possible to understand the exact causes of SARA. Animal management seems to be one of the most important factors in developing SARA including total mixed ration preparation.     

Increased blood concentration of isopropanol in ketotic dairy cows and isopropanol production from acetone in the rumen

To evaluate acetone and isopropanol metabolism in bovine ketosis, the blood concentrations of isopropanol, acetone, plasma 3-hydroxybutyrate (3-HB) and other metabolites were analyzed in 12 healthy controls and 15 ketotic dairy cows including fatty liver and inferior prognosis after laparotomy for displaced abomasum. In ruminal fluid taken from 6 ketotic cows, ruminal isopropanol and acetone were also analyzed. Ketotic cows showed higher concentrations of isopropanol, acetone, 3-HB and nonesterified fatty acid, and higher activities of aspartate transaminase and γ-glutamyl transferase than control cows. Blood samples had higher concentration of isopropanol accompanied by increased acetone. In the ketotic cows, acetone was detected not only in blood but also in ruminal fluid, while higher ruminal isopropanol did not necessarily accompany its elevation in the blood. Using 2 steers with rumen cannula, all ruminal content was emptied and then substituted with artificial saliva to evaluate the importance of ruminal microbes in isopropanol production. Under each condition of intact and emptied rumen, acetone was infused into the rumen and blood isopropanol was analyzed. The elevation in the blood isopropanol concentration after acetone infusion was markedly inhibited by the emptying. Here, increased blood concentrations of isopropanol and acetone were observed in ketotic cows, and the importance of ruminal microbes in isopropanol production was confirmed.     

壳聚糖在奶牛瘤胃中的降解率及其对瘤胃发酵的影响

试验旨在研究壳聚糖在奶牛瘤胃中的降解率及其对瘤胃发酵的影响。选择3头体况良好,年龄、体重、胎次、泌乳期相近,安装永久性瘤胃瘘管的荷斯坦泌乳牛作为供体牛。试验一采用尼龙袋法,分别在投入尼龙袋后2、4、8、12、24、36、72 h取样,测定壳聚糖在瘤胃内的实时降解率。试验二利用体外批次培养法,采用单因素完全随机试验设计依据壳聚糖在基础培养底物中的添加剂量分为6个处理组(0、0.02%、0.1%、0.5%、1%、2%)。其中,零剂量组为对照组,其余为壳聚糖组。分别于培养0、2、4、8、12、24 h时间点取样,研究不同添加水平的壳聚糖对奶牛瘤胃液体外发酵特性的影响。结果表明:壳聚糖在奶牛瘤胃内降解率很低,在72 h时的降解率仅有7.79%;添加不同水平的壳聚糖,对奶牛瘤胃体外发酵培养液的pH值、NH3-N浓度、菌体蛋白(BCP)含量、挥发性脂肪酸(VFA)含量、产气量均无显著的影响(P>0.05)。     

The effect of feed regimen on chewing time, digesta passage rate and particle size distribution in Holstein non-lactating cows fed pasture ad libitum

The objective of this study was to evaluate the effect of feeding regimen on chewing activity and ruminal passage of digesta in non-lactating cows fed pasture ad libitum. Six ruminally fistulated Holstein dry cows (mean ± SD; parity = 3.7 ± 0.5, length of pregnancy = 28 ± 2 W, BW = 692 ± 75 kg) were assigned randomly to two dietary treatments using a crossover design; three cows were rotationally grazed pasture (treatment G) and the other was fed harvested pasture ad libitum in confinement (treatment C). Passage of digesta was measured by fecal marker excretion using Co-EDTA and Dysprosium (Dy) labeled grass as fluid phase maker or solid phase marker, respectively. Particle size distribution of ruminal digesta and feces was measured by wet sieving method. No significant difference in dry matter intake (DMI) between treatments was observed. Eating time in treatment G (517 min/day or 38.6 min/kg DMI) was longer treatment C (384 min/day or 31.0 min/kg DM). Chewing time per DMI was similar in both treatments (70.0 vs. 66.1 min/kg DMI). Ruminal liquid outflow rate and rumen volume of cows in treatment G were significant higher and lower than treatment C (9.9 vs. 12.2%/h and 111.0 vs. 79.9 L, respectively). The mean retention time in small particle pool to be able to pass through the reticulo-omasum orifice (CMRT₂) in cows of treatment C was longer (P < 0.05) than that for treatment G.. Logarithmic particle distribution and mean particle size of ruminal digesta at 24 h after feeding and feces particles had no significance between treatments. These results indicated that ingestive behavior of dry cow affected on eating time and ruminal volume, and it might have caused the higher ruminal liquid and particulate passage rate in treatment G compare to treatment C, with minimal effect on the particle size of digesta to pass from the rumen.     

不同水平螺旋藻对奶牛瘤胃内环境及日粮营养成分降解率的影响

[目的]为了探索不同水平螺旋藻对奶牛瘤胃pH值、氨氮浓度和日粮营养成分瘤胃降解率的影响。[方法]本试验选择三头安装永久性瘤胃瘘管的成年奶牛,采用3×3拉丁方试验设计进行饲养试验。试验处理S1组为基础日粮,S2组为基础日粮＋0.09%DM螺旋藻,S3组为基础日粮＋0.15%DM螺旋藻。[结果]添加0.09%和0.15%DM的螺旋藻对瘤胃pH值无显著影响（P〉0.05）,有降低氨氮浓度趋势,但与对照组比较差异不显著（P〉0.05）;两个添加组对日粮DM瘤胃有效降解率也没有显著影响（P〉0.05）,但显著提高了日粮NDF、ADF瘤胃降解率（P〈0.05）,0.15%DM螺旋藻还可显著降低日粮CP瘤胃降解率（P〈0.05）。[结论]表明适量添加螺旋藻不影响奶牛瘤胃发酵内环境,但具有显著提高日粮纤维物质的瘤胃降解率和降低日粮蛋白质降解作用。     

归芪益母复方制剂对产后奶牛瘤胃微生物和短链脂肪酸的调节

本试验旨在探究归芪益母复方制剂对产后奶牛瘤胃微生物和短链脂肪酸的调节作用。将19头待产的健康荷斯坦奶牛随机分为两组,对照组10头,试验组9头。试验组奶牛产后每天灌服归芪益母复方制剂500 mL,对照组奶牛每天灌服等体积饮用水,连续6 d。产后第7天晨饲前采集瘤胃液,采用16S rRNA高通量测序和GC-MS/MS靶向代谢组学技术对两组奶牛瘤胃菌群的丰度和短链脂肪酸的含量进行了测定。结果表明,与对照组相比,试验组奶牛瘤胃变形菌门(Proteobacteria)、Escherichia-Shigella属和拟杆菌属(Bacteroides)的菌群丰度极显著升高(P<0.01),乳杆菌属(Lactobacillus)和Subdoligranulum属菌群丰度显著升高(P<0.05)。试验组奶牛瘤胃丙酸(P<0.05)和异丁酸(P<0.01)含量明显升高。本研究从瘤胃微生物菌群及短链脂肪酸角度揭示了归芪益母方对产后奶牛的保健机制。     

Effects of time of day and monensin on the size distribution of particles in digestive tract sites of heifers fed corn silage

Effects of time of day and dietary monensin in the distribution of size of digesta particles in different digestive tract sites and their intersite relationships were examined in six heifers (290 kg BW) with ruminal, duodenal and ileal cannulas given ad libitum access to corn silage, with or without 100 mg monensin.head-1.d-1, in a two-period crossover design. Ingestive masticate and digesta of corn silage were collected via esophageal, ruminal or intestinal cannulas. The distribution of particulate matter retained on sieves with apertures larger than 20 microm was determined by wet-sieving. The cumulative distribution of particulate matter on a series of sieves was regressed on retaining sieve aperture to estimate the sieve aperture that would retain 50% weight of the particulate matter (median retaining aperture, MRA). The MRA of masticate was 6,494 microm. The MRA of digesta particles decreased (P less than .05) from ventral rumen (1,847 microm) to dorsal rumen (1,797 microm) to duodenum (346 microm), but increased to the rectum (359 microm). The MRA was lower (P = .044) for the monensin treatment only in feces. The MRA of particulate matter in the dorsal and ventral rumen, duodenum and rectum all changed (P less than .05) over 24 h. An inverse pattern between the MRA of ruminal and duodenal digesta occurred, presumably the result of a nycterohemeral pattern of eating and ruminating activity. Across sampling times, an inverse relationship existed between MRA of ventral rumen and duodenal digesta. This relationship suggests that a ruminal digesta raft composed of larger particles (immediately following major meals) is more effective than a raft of smaller particles (prior to such meals) in preventing flux of large particles to the duodenum.     

奶牛低淀粉型日粮研究进展

低淀粉型日粮的应用不仅可以满足高产奶牛生产阶段的能量需要,而且可以保证奶牛瘤胃健康,避免瘤胃酸中毒。常用低淀粉型饲料有优质牧草、中性洗涤可溶性纤维源饲料以及可溶性糖三大部分。饲喂低淀粉型日粮可以有效缓解挥发性脂肪酸的产生,避免瘤胃pH降低,并促进了奶牛的采食以及养分消化,提高乳品质。本文从低淀粉型日粮的实现手段,以及瘤胃发酵参数和生产性能方面阐述低淀粉型日粮在奶牛生产中的必要性,确立今后的研究重点应该在各种原料替代谷物原料的最适比例及组合效应方面,从而完善奶牛低淀粉型日粮配制技术。     

Composition and digestive tract retention time of ruminal particles with functional specific gravity greater or less than 1.02

The objective of this study was to determine composition, particle size distribution, and in vivo kinetics of ruminal particles having functional specific gravity (FSG) greater or less than FSG of particles found in the omasum and reticulum of lactating dairy cows. Particles from the reticulum and the omasal had FSG of 1.03 and 1.02, respectively. Particles from ruminal contents with FSG higher (HP) or lower (LP) than 1.02 were isolated and labeled with Er or Dy, respectively. Four ruminally cannulated, lactating Ayrshire dairy cows were fed all-grass silage (AS) or 54% grass silage:46% concentrate (SC) diets in a cross-over design trial and used to study chemical composition and ruminal and total tract kinetics of HP and LP. Labeled particles were pulse dosed into the rumen of the cows and disappearance of the markers from ruminal HP and LP pools and excretion in feces was monitored for 72 and 120 h, respectively. Fecal marker excretion data were fitted using two-compartment mathematical age-dependent/age-independent (Gn-->G1) models. Inclusion of concentrate in the diet (SC) increased (P < 0.05) apparent total tract digestibility of dietary DM, OM and N. Digestibility of fiber fractions, NDF and ADF, was lower (P < 0.01 and P < 0.05, respectively) for SC compared with AS. The heavy particles had higher (P < 0.01) indigestible NDF and lower (P < 0.01) N concentration than LP. Particles from the HP pool passed from the rumen more rapidly (P < 0.01) than particles from LP (0.044 and 0.019 h(-1), respectively). Diet had no effect on particle rate of disappearance or pool size in the rumen. Across diets, pool size of LP was consistently larger (P < 0.05) than that of HP. Diet had no effect on total tract mean retention time (MRT) of LP or HP. Total tract MRT of LP was greater (P < 0.05) than MRT of HP (59.6 vs. 49.0 h, respectively). Results from this study support the hypothesis that functional specific gravity is an important factor determining the rate of outflow and residence time of feed particles within the reticulo-rumen and total digestive tract. Our data indicate that digesta particles with functional specific gravity greater or less than 1.02 have different composition and flow characteristics. Heavier particles contain more indigestible fiber and less N and are likely depleted of substrate available for microbial fermentation, are smaller in size, and have a higher passage rate/shorter retention time in the digestive tract than lighter particles.