Pediococcus acidilactici isolated from the rumen of lambs with rumen acidosis, 16S rRNA identification and sensibility to monensin and lasalocid

A lactic-acid producing bacterium was isolated from the rumen of lambs with rumen acidosis. The cells were Gram-positive, nonmotile, nonsporing, catalase negative spherical, 1.5-2.0 μm in diameter, and occur in pairs and tetrads. Analysis of 16S ribosomal RNA indicated that the rumen bacterium was a strain of Pediococcus acidilactici with 99% of nucleotide homology. This bacterium was sensible to monensin and lasalocid at the unique dose tested of 300 ppm. The concentration of lactic acid and DM degradation decreased (P < 0.05) when monensin or lasalocid were added to the culture media after 24, 48 and 72 h of incubation. In contrast, total VFA concentration and pH were higher (P < 0.05) in the culture media added with the ionophores. Up to now S. bovis is considered the main ruminal bacterium related with rumen acidosis, but the importance of P. acidilactici should be also reconsidered in experimental studies focused on the control rumen acidosis.     

Regulation of lactate metabolism in the rumen

The regulation of lactic acid production, the regulation of lactate fermentation and the role of lactate as intermediate in the rumen metabolism was studied.The pH had a pronounced effect on all three processes and therefore buffer capacity of the rumen contents is also described.Starch gave much less rise to lactic acidosis than soluble sugars, as glucose and fructose. Most bacteria grow faster and therefore produce more lactic acid when amino acids and/or soluble proteins are present in the diet.Activity of LDH (lactate dehydrogenase) of mixed rumen microorganisms is regulated by the NADH/NAD (H) balance and the ATP concentration. About 60% of the LDH in mixed rumen microorganisms is fructose-1, 6-diphosphate independent. Megasphaera elsdenii ferments 60 to 80% of the lactate fermented in the rumen of dairy cattle.Lactate accumulates only when the glycolytic flux (hexose units fermented per unit time per microorganism) is high. During adaptation, the glycolytic flux is increased and lactate may accumulate. After adaptation to a certain diet, the number of microorganisms is changed and the glycolytic flux again is normal and lactate is only a minor intermediate in rumen metabolism.     

Efficacy of Megasphaera elsdenii inoculation in subacute ruminal acidosis in cattle

Two consecutive experiments were carried out to determine efficacy of Megasphaera elsdenii inoculation in alleviation of subacute ruminal acidosis (SARA). In the first experiment, SARA was induced by feeding corn‐ and wheat‐based diets (20%, 40%, 60% and 80% of TMR, DM basis) in six ruminally cannulated heifers. Continuous pH was obtained using data loggers embedded in rumen. In corn (80%)‐ and wheat (60%)‐based diets ruminal pH ranged from 5.2 to 5.6 for 7.77 and 5.93 hr. In the second experiment (5 day), M. elsdenii (200 ml; 2.4 x 10¹⁰ cfu/ml) was inoculated during the first two days. During the SARA induction period, M. elsdenii and S. bovis in rumen liquor were more abundant in wheat‐based feeding (7.97 and 8.77) than in corn‐based feeding (7.06 and 7.95 per ml, log basis; p < 0.0001 for both). M. elsdenii inoculation increased total volatile fatty acids (VFA) concentration when corn‐based diet was fed, whereas it decreased total VFA concentration when wheat‐based diet was fed (p < 0.004). There was a decrease in the propionic acid proportion (24.04%–19.08%; p < 0.002), whereas no alteration in lactate and ammonia concentrations was observed. M. elsdenii inoculation increased protozoa count (from 5.39 to 5.55 per ml, log basis; p < 0.009) and decreased S. bovis count (from 9.18 to 7.95 per ml, log basis; p < 0.0001). The results suggest that M. elsdenii inoculation may help prevent SARA depending on dietary grain through altering rumen flora as reflected by a decrease in S. bovis count and an increase in protozoa count.     

瘤胃中乳酸的代谢及其调控机制

有关瘤胃酸中毒发生机制研究表明,瘤胃乳酸的累积可能对酸中毒诱导起重要作用,而高精料日粮下瘤胃乳酸累积主要取决于瘤胃乳酸产生菌和乳酸利用菌间的平衡程度。本文综述了瘤胃微生物对乳酸的代谢机制,包括主要乳酸产生菌[溶纤维丁酸弧菌(Butyrivibrio fibrisolvens)、牛链球菌(Streptococcus bovis)、乳酸杆菌(Lactobacillus)]和主要乳酸利用菌[反刍兽新月单胞菌(Selenomonus ruminantium)、埃氏巨型球菌(Megasphaera elsdenii)],并简要概述了酸中毒的调控方法,旨在为反刍动物瘤胃酸中毒的乳酸中毒机制深入解析提供参考。     

Ruminal lactic acidosis in sheep and goats.

The clinical findings in 37 sheep and goats with acute ruminal lactic acidosis included a disturbed general condition characterised by anorexia, apathy, teeth grinding and muscle twitching, ruminal stasis, and the excretion of soupy or watery faeces. The ruminal fluid of affected animals was milky, had a sour odour and a low pH. There was a predominance of Gram-positive bacteria in smears of ruminal fluid. In comparison with 10 control animals, the rumen fluid of 23 sheep with ruminal lactic acidosis had higher lactic acid and lower volatile fatty acid concentrations. In addition, the affected animals often had haemoconcentration and metabolic acidosis. Treatment included single or repeated transfer of ruminal fluid from healthy cows and, depending on the severity, the administration of antacids, yeast and chlortetracycline, and the intravenous infusion of isotonic sodium chloride and 5 per cent sodium bicarbonate solutions. Of the 37 treated sheep and goats, four died within 24 hours, and three others were euthanased after one, two and three days because their condition rapidly deteriorated. Thirty animals were discharged one to nine days after treatment. Twenty-nine of them (78.4 per cent) recovered completely but one was euthanased later.     

Influence of malic acid supplementation on ruminal pH, lactic acid utilization, and digestive function in steers fed high-concentrate finishing diets

Two trials were conducted to evaluate the influence of malic acid supplementation on ruminal fermentation. In Trial 1, six Holstein steers (300 kg) with ruminal cannulas were used in a crossover design experiment to study the influence of malic acid (MA) on ruminal metabolism during glucose-induced lactic acidosis. Treatments consisted of a 77% steam-flaked barley-based finishing diet supplemented to provide 0 or 80 g/d of MA. After a 13-d dietary adjustment period, 1 kg of glucose was infused into the rumen 1 h after the morning feeding. Ruminal pH was closely associated (R2 = .70) with ruminal DL-lactate concentration. Malic acid supplementation increased (P < .01) ruminal pH 3 h after the glucose infusion. However, there were no treatment effects (P > .10) on ruminal VFA molar proportions or ruminal and plasma DL-lactate concentrations. In Trial 2, four Holstein steers (150 kg) with cannulas in the rumen and proximal duodenum were used in a crossover design experiment to evaluate the influence of MA supplementation on characteristics of digestion. Treatments consisted of an 81% steam-flaked barley-based finishing diet supplemented to provide 0 or 80 g/d of MA. There were no treatment effects (P > .10) on ruminal and total tract digestion of OM, ADF, starch, and feed N or on ruminal microbial efficiency. Malic acid supplementation increased (P < .05) ruminal pH 2 h after feeding. As with Trial 1, there were no treatment effects (P > .10) on ruminal VFA and DL-lactate concentrations. We conclude that supplementation of high-grain finishing diets with MA may be beneficial in promoting a higher ruminal pH during periods of peak acid production without detrimental effects on ruminal microbial efficiency or starch, fiber, and protein digestion. There were no detectable beneficial effects of MA supplementation on ruminal and plasma lactic acid concentrations in cattle fed high-grain diets.     

瘤胃源酵母的分离筛选及对不同底物发酵能力影响

本实验旨在分离筛选瘤胃源酵母,研究其对不同饲料底物的发酵特性。实验以山羊及奶牛瘤胃液为菌源,利用酵母选择性培养基,通过分离筛选、生长曲线测定和26S rDNA鉴定,获得1株生长速度较快的Meyerozyma属酵母菌株。在此基础上,采用体外发酵技术,分别以羊草与精料混合物、马铃薯淀粉和玉米淀粉为底物,以奶牛瘤胃液为接种物,研究该酵母菌株对瘤胃微生物体外发酵参数的影响。结果表明,在以羊草和精料混合物为底物时,添加瘤胃源酵母显著降低了发酵液pH和乳酸浓度(P<0.001),显著提高了丙酸浓度和干物质消失率(P<0.05);以玉米淀粉为底物时,添加该酵母菌显著降低了发酵液pH和乳酸浓度(P<0.001);以马铃薯淀粉为底物时,显著降低了pH(P<0.05),提高了丙酸浓度(P<0.05);但在上述3种底物条件下,添加酵母菌对发酵液中总产气量、氨态氮、乙酸、丁酸、异丁酸、戊酸和异戊酸浓度无显著影响(P>0.05)。采用Real-time PCR测定结果表明,添加该酵母菌可显著提高以羊草和马铃薯淀粉为底物时发酵液中总菌16S rDNA的挎贝数(P<0.05)。结果说明,本研究分离获取的瘤胃源酵母可提高瘤胃微生物对羊草精料混合物的降解能力,降低羊草精料混合物组和玉米淀粉组发酵液中乳酸浓度,提示该菌株可能具有提高日粮消化利用效率、促进丙酸生成和瘤胃细菌生长的作用。     

Responsive changes of rumen microbiome and metabolome in dairy cows with different susceptibility to subacute ruminal acidosis

Subacute ruminal acidosis(SARA)represents one of the most important digestive disorders in intensive dairy farms,and dairy cows are individually different in the severity of SARA risk.The objectives of the current study were to investigate differences in the ruminal bacterial community and metabolome in dairy cattle with different susceptibility to SARA.In the present study,12 cows were initially enrolled in the experiment.Based on average ruminal pH,4 cows with the lowest ruminal pH were assigned to the susceptible group(SUS,pH=5.76,n=4)and 4 cows with the highest ruminal pH assigned to the tolerant group(TOL,pH=6.10,n=4).Rumen contents from susceptible(SUS,n=4)and tolerant(TOL,n=4)dairy cows were collected through rumen fistula to systematically reveal the rumen microbial and metabolic alterations of dairy cows with different susceptibility to SARA using multi-omics approaches(16S and 18S rRNA gene sequencing and metabolome).The results showed that despite being fed the same diet,SUS cows had lower ruminal pH and higher concentrations of total volatile fatty acids(VFA)and propionate than TOL cows(P<0.05).No significant differences were observed in dry matter intake,milk yield,and other milk compositions between the SUS and TOL groups(P>0.05).The principal coordinates analysis based on the analysis of molecular variance indicated a significant difference in bacterial composition between the two groups(P=0.01).More specifically,the relative abundance of starch-degrading bacteria(Prevotella spp.)was greater(P<0.05),while the proportion of fiber-degrading bacteria(unclassified Ruminococcaceae spp.,Ruminococcus spp.,Papillibacter,and unclassified Family_-XIII)was lower in the rumen of SUS cows compared with TOL cows(P<0.05).Community analysis of protozoa showed that there were no significant differences in the diversity,richness,and community structure(P>0.05).Metabolomics analysis revealed that the concentrations of organic acids(such as lactic acid),biogenic amines(such as histamine),and bacterial degradation products(such as hypoxanthine)were significantly higher in the SUS group compared to the TOL group(P<0.05).These findings revealed that the higher proportion of starch-degrading bacteria/lower fiber-degrading bacteria in the rumen of SUS cows resulted in higher VFA-producing capacity,in particular propionate.This caused a disruption in metabolic homeostasis in the rumen which might be the reason for the higher susceptibility to SARA.Overall,these findings enhanced our understanding of the ruminal microbiome and metabolic changes in cows susceptible to SARA.     

Stimulation of butyrate production through the metabolic interaction among lactic acid bacteria, Lactobacillus acidophilus, and lactic acid-utilizing bacteria, Megasphaera elsdenii, in porcine cecal digesta

In this study, we examined the potential of Megasphaera elsdenii as a probiotic agent in combination with sodium gluconate. We also examined the combination of M. elsdenii with probiotic lactic acid bacteria (LAB), Lactobacillus acidophilus, to enhance butyrate production in the large intestine using a pig cecal in vitro model under the presence of sodium gluconate. Compared to the uninoculated control culture (with only diluted cecal digesta), the addition of M. elsdenii and LAB to the culture stimulated significantly the production of n‐butyrate (60% increase) and n‐valerate (50% increase) after 24 h incubation. n‐Butyrate is regarded as the most important short‐chain fatty acid in the large intestine because it stimulates the proliferation of epithelial cells, mucus release and water and mineral absorption. Therefore, lactate‐utilizing butyrate producers such as M. elsdenii play a significant role in supporting the health‐beneficial effects of lactogenic prebiotics and probiotics LAB. The potential of M. elsdenii as a probiotic was also suggested.     

Anti-lipopolysaccharide antibody administration mitigates ruminal lipopolysaccharide release and depression of ruminal pH during subacute ruminal acidosis challenge in Holstein bull cattle

The effects of anti-lipopolysaccharide (LPS) antibody on rumen fermentation and LPS activity were investigated during subacute ruminal acidosis (SARA) challenge. Eleven Holstein cattle (164 ± 14 kg) were used in a 3 × 3 Latin square design. Cattle were fed a roughage diet on days −11 to −1 (pre-challenge) and day 2 (post-challenge), and a high-grain diet on days 0 and 1 (SARA challenge). For 14 days, 0-, 2-, or 4-g of anti-LPS antibody was administered once daily through a rumen fistula. Ruminal pH was measured continuously, and rumen fluid and blood samples were collected on days −1, 0, 1, and 2. Significantly lower ruminal LPS activity on day 1 was observed in the 2- and 4-g groups than those in the 0-g group. In addition, significantly higher 1-hr mean ruminal pH on SARA challenge period (days 0 and 1) was identified in the 4-g group than in the 0-g group. However, rumen fermentation measurements (total volatile fatty acid [VFA], VFA components, NH₃-N and lactic acid) and peripheral blood metabolites (glucose, free fatty acid, beta-hydroxybutyrate, total cholesterol, blood urea nitrogen, aspartate aminotransferase and gamma-glutamyl transferase) were not different among the groups during the experimental periods. Therefore, anti-LPS antibody administration mitigates LPS release and pH depression without the depression of rumen fermentation and peripheral blood metabolites during SARA challenge in Holstein cattle.     

Diagnosis of subacute ruminal acidosis (SARA) by continuous reticular pH measurements in cows

The objective of this study was to determine whether subacute ruminal acidosis (SARA) could be diagnosed by continuous measurements of the reticular pH, as compared with the ruminal pH, using healthy cows fed a control diet and SARA cows fed a rumen acidosis-inducing diet. The reticular and ruminal pH were measured simultaneously by a radio transmission pH measurement system. The mean reticular pH at 1-h intervals decreased gradually from the morning feeding to the next feeding time in both healthy and SARA cows, though the decrease in the ruminal pH was observed to be more drastic as compared with that observed in the reticular pH. The threshold of the 1-h mean pH in the reticulum for a diagnosis of SARA was considered to be 6.3, and a significant positive correlation was observed between the reticular and ruminal pH. No differences in the concentrations of lactic acid, ammonia nitrogen, and volatile fatty acids were noted between the reticular and ruminal fluids in SARA cows. These results demonstrate that the reticular pH can be used to detect SARA in cows, as opposed to using the ruminal pH.     

Oxidative response of neutrophils to platelet-activating factor is altered during acute ruminal acidosis induced by oligofructose in heifers

Reactive oxygen species (ROS) production is one of the main mechanisms used to kill microbes during innate immune response. D-lactic acid, which is augmented during acute ruminal acidosis, reduces platelet activating factor (PAF)-induced ROS production and L-selectin shedding in bovine neutrophils in vitro. This study was conducted to investigate whether acute ruminal acidosis induced by acute oligofructose overload in heifers interferes with ROS production and L-selectin shedding in blood neutrophils. Blood neutrophils and plasma were obtained by jugular venipuncture, while ruminal samples were collected using rumenocentesis. Lactic acid from plasma and ruminal samples was measured by HPLC. PAF-induced ROS production and L-selectin shedding were measured in vitro in bovine neutrophils by a luminol chemiluminescence assay and flow cytometry, respectively. A significant increase in ruminal and plasma lactic acid was recorded in these animals. Specifically, a decrease in PAF-induced ROS production was observed 8 h after oligofructose overload, and this was sustained until 48 h post oligofructose overload. A reduction in PAF-induced L-selectin shedding was observed at 16 h and 32 h post oligofructose overload. Overall, the results indicated that neutrophil PAF responses were altered in heifers with ruminal acidosis, suggesting a potential dysfunction of the innate immune response.     

Ruminal lactic acidosis: relationship of forestomach motility to nondissociated volatile fatty acids levels

Ruminal lactic acidosis was produced in 9 overnight fasted rumen-fistulated sheep by placing ground wheat (40 g/kg of body weight) into the rumen. Ruminal stasis occurred within 8 hours of grain engorgement in 6 sheep (early stasis group) and between 10 and 12 hours in the remaining 3 sheep (late stasis group). The initial impairment to forestomach motility was a decrease in the mean frequency of reticulo-ruminal contractions which occurred within 4 hours of the intraruminal placement of wheat in the early stasis group and within 6 hours in the late stasis group. Since blood pH, carbon dioxide pressure, and serum bicarbonate were all normal, systemic acidosis was not a contributing factor to this decrease in contraction frequency. The concentrations of total nondissociated volatile fatty acids (VFA; acetic, propionic, and butyric acid) in ruminal fluid, however, were significantly increased, being 13.60 mM/L (mean, pH 4.92) in the early stasis group and 15.77 mM/L (pH 4.80) in the late stasis group. Free DL-lactic acid in ruminal fluids was 6.37 +/- 6.1 mM/L (mean +/- SD) in the early stasis group and 9.72 +/- 4.2 mM/L in the late stasis group. A reduction in contraction amplitude was observed within 6 hours of grain engorgement in the early stasis group and within 8 hours in the late stasis group. At these times, the concentrations of nondissociated VFA were 10.19 mM/L (pH 4.46) in the early stasis group and 10.52 mM/L (pH 4.62) in the late stasis group. The ruminal values of free DL-lactic acid were 13.93 mM/L in the early stasis group and 16.14 mM/L in the late stasis group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of Saccharomyces cerevisiae on ruminal pH and microbial fermentation in dairy cows: Yeast supplementation on rumen fermentation

An experiment was conducted with eight ruminally-cannulated cows using a crossover design with 2 periods to determine the effects of yeast supplementation on rumen fermentation. Holstein dairy cows in late lactation were either supplemented with 0.5 g/hd/d of Saccharomyces cerevisiae, an active dry yeast (CNCM-1077, Levucell SC20 (r) SC, Lallemand Animal Nutrition) or not supplemented (control). A basal diet consisting of 60% forage and 40% concentrate (DM basis) was fed once daily to both groups of cows throughout the entire experiment. Ruminal pH was measured continuously every 22 min using a pH probe that was placed in the ventral rumen sac for 6 consecutive days. Volatile fatty acid and ammonia N concentrations in the rumen were measured on days 5 or 6 of the 12-d period for each cow and DM intake was monitored throughout the experiment. Data were analyzed using a mixed-effects model with repeated measures. There were no differences in dry matter intake between treatments. Mean ruminal pH was greater (P < 0.05) when yeast was supplemented (6.53 ± 0.07) compared with the control (6.32 ± 0.07). Average maximum and minimum ruminal pH were also greater (P < 0.05) when yeast was supplemented (7.01 ± 0.09 and 5.97 ± 0.08, respectively) compared with the control (6.80 ± 0.09 and 5.69 ± 0.09, respectively). Time spent under the subacute acidosis threshold, pH less than 5.6, was lower (P < 0.05) with yeast supplementation compared with control cows. No difference was observed for ruminal ammonia N concentrations (mean = 14.0 ± 1.2 mg/dL) between treatments. Total VFA concentration (mM) in the rumen tended to be lower (P = 0.10) in the yeast-supplemented cows (107.3 ± 6.35) than in the control cows (122.4 ± 6.35), which could be related to the greater pH observed with yeast supplementation. Supplementing dairy cows with active dry yeast in the current experiment increased the mean, minimum and maximum ruminal pH; decreased time spent in subacute rumen acidosis, and tended to decrease total VFA concentration in the rumen compared with control cows.     

高精料诱导的SARA对泌乳期山羊血液和瘤胃液中皮质醇的影响

选择7只装有永久性瘤胃瘘管的泌乳中期山羊,2×2拉丁方设计,分别饲喂精粗比为6∶4和4∶6的饲料,通过饲喂精粗比6∶4饲料建立泌乳期山羊瘤胃亚急性酸中毒(subacute ruminal acidosis, SARA)模型,研究SARA时山羊血液和瘤胃液中皮质醇浓度、肝脏皮质醇受体(glucocorticoid receptor, GR)mRNA表达及其他相关指标的变化。结果表明,精粗比6∶4日粮饲喂2周后成功诱导SARA状态(SARA组),采食后瘤胃液pH值低于5.8持续时间约6 h,而精粗比为4∶6组山羊瘤胃液pH均高于6.0 (对照组)。高精料日粮处理对瘤胃pH和乳酸以及瘤胃液和血浆内的脂多糖、皮质醇浓度有显著性影响(P<0.05),采食前SARA组山羊瘤胃液中乳酸浓度显著高于对照组(P<0.05),采食后0~4 h乳酸含量下降,6~10 h时逐渐增加并极显著高于对照组(P<0.01);2组间瘤胃液中脂多糖浓度无显著性差异(P>0.05),SARA组血浆脂多糖浓度在采食前和采食后6 h均显著高于对照组(P<0.05);采食前SARA组山羊血液中皮质醇浓度高于对照组(P=0.05),但采食后6 h两组间无显著差异(P>0.05); 2组山羊瘤胃液中皮质醇浓度在采食后2,4和6 h分别显著高于对照组(P<0.05),但在采食前和采食后10 h无显著差异(P>0.05)。Real-time PCR结果显示,SARA组山羊肝脏中GR mRNA表达显著下调(P<0.05)。本研究结果显示,泌乳期山羊发生SARA时糖皮质激素水平升高,负反馈下调肝脏GR的表达水平,提示SARA时机体处于应激状态,可能引起肝脏的物质代谢和营养物质重分配的改变。     

Ruminant Nutrition Symposium: Role of fermentation acid absorption in the regulation of ruminal pH

Highly fermentable diets are rapidly converted to organic acids [i.e., short-chain fatty acids (SCFA) and lactic acid] within the rumen. The resulting release of protons can constitute a challenge to the ruminal ecosystem and animal health. Health disturbances, resulting from acidogenic diets, are classified as subacute and acute acidosis based on the degree of ruminal pH depression. Although increased acid production is a nutritionally desired effect of increased concentrate feeding, the accumulation of protons in the rumen is not. Consequently, mechanisms of proton removal and their quantitative importance are of major interest. Saliva buffers (i.e., bicarbonate, phosphate) have long been identified as important mechanisms for ruminal proton removal. An even larger proportion of protons appears to be removed from the rumen by SCFA absorption across the ruminal epithelium, making efficiency of SCFA absorption a key determinant for the individual susceptibility to subacute ruminal acidosis. Proceeding initially from a model of exclusively diffusional absorption of fermentation acids, several protein-dependent mechanisms have been discovered over the last 2 decades. Although the molecular identity of these proteins is mostly uncertain, apical acetate absorption is mediated, to a major degree, via acetate-bicarbonate exchange in addition to another nitrate-sensitive, bicarbonate-independent transport mechanism and lipophilic diffusion. Propionate and butyrate also show partially bicarbonate-dependent transport modes. Basolateral efflux of SCFA and their metabolites has to be mediated primarily by proteins and probably involves the monocarboxylate transporter (MCT1) and anion channels. Although the ruminal epithelium removes a large fraction of protons from the rumen, it also recycles protons to the rumen via apical sodium-proton exchanger, NHE. The latter is stimulated by ruminal SCFA absorption and salivary Na(+) secretion and protects epithelial integrity. Finally, SCFA absorption also accelerates urea transport into the rumen, which via ammonium recycling, may remove protons from rumen to the blood. Ammonium absorption into the blood is also stimulated by luminal SCFA. It is suggested that the interacting transport processes for SCFA, urea, and ammonia represent evolutionary adaptations of ruminants to actively coordinate energy fermentation, protein assimilation, and pH regulation in the rumen.     

Effect of amount and degradability of dietary starch on animal performance and meat quality in beef bulls

Introduction   Even at a similar energy concentration of the diet, energy source may affect animal performance. O wens et al. (1997) reported that daily dry matter (DM) intake tended to be lowest for wheat-based diets and highest for milo and oat-based diets. O'M ara et al. (1997) found a lower pH and less ammonia in the rumen of lactating cows, when unmolassed beet pulp was replaced with ground wheat. Contrary to the results of O'M ara et al. (1997), M alestein et al. (1984) found a greater risk for lactic acidosis for citrus and beet pulp than for maize meal and tapioca. For years it has been known that rapidly degradable carbohydrates may provoke acidosis (H untington and B ritton 1979; F iems et al. 1993). Furthermore, low ruminal pH may inhibit cellulose digestion (M ould et al. 1983) and decrease efficiency of microbial protein synthesis (R ussell et al. 1979).
As energy concentration of the diet is important for finishing cattle (B oucqu & eacute ; et al. 1980), the amount of roughage is rather limited. This may result in sub-clinical acidosis with a negative impact on animal performance (O wens et al. 1998), especially when the diet is rich in rapidly fermentable carbohydrates. Therefore an experiment was conducted to investigate the impact of energy source in the finishing diet on voluntary daily feed intake, daily liveweight gain, feed efficiency, blood metabolites and carcass quality.
Energy source may also affect meat quality. C asteels et al. (1969) found differences in meat colour when concentrates were based on cereals or sugarbeet pulp. W ood (1984) reported that the concentrate : forage ratio in the diet affects the fatty acid composition of body fat through an increase in propionate production in the rumen. Therefore the effect on meat quality was also studied.     

An Evaluation of Parameters for the Detection of Subclinical Rumen Acidosis in Dairy Herds

An observational study was conducted in six Danish dairy herds. A specially designed stomach tube was compared to the rumenocentesis technique as part of the monitoring of rumen pH. In contrast to a previous study, the use of the stomach tube appeared to reduce saliva contamination. However, correlation with the rumenocentesis technique was poor ( r = 0.33; p = 0.019) and a linear model could only partly explain variations between either results. The presence of subclinical rumen acidosis (SRA) was evidenced in one herd only, as judged by results obtained by the rumenocentesis technique. The present study revealed some limitations of the rumenocentesis technique in small or medium-sized herds due to difficulties in selecting sufficient numbers of cows in the respective groups at risk. The finding of two apparently clinical normal cows with rumen pH values below 5.0 leads to the consideration that such fluctuations may be temporary and at least does not give rise to clinical symptoms. However, the long-term effect of such fluctuations is not known. In general, primiparous cows seemed more prone to low ruminal pH values (< 6.0), higher ruminal concentrations of short-chain fatty acids, and possibly to metabolic acidosis, than were multiparous cows. Ruminal propionate was the most precise predictor of rumen pH, whereas milk fat percentage varied greatly between lactational groups. Blood lactate dehydrogenase (LDH), beta-hydroxybutyrate (BHB) and fructosamine as well as urine phosphorus excretion and renal net acid-base excretion (NABE) were related to ruminal acid load, but were not predictive of rumen pH. Monitoring of dairy herds for SRA should be performed routinely and employ several diagnostic tools (rumenocentesis, renal NABE determination) as well as specific knowledge of herd management and feeding routines.     

Effect of dietary lactic acid on rumen lactate metabolism and blood acid-base status of lambs switched from low to high concentrate diets.

Two experiments were conducted with ruminally fistulated wether lambs to determine the effect of lactic acid addition to a hay diet on rumen lactate metabolism, blood acid-base status and subsequent adaptation to a high concentrate diet. In Exp. 1, lambs were fed mature brome hay (H), H plus 5% (w/w) D,L lactic acid (H5L) or H plus 10% lactic acid (H10L) (three lambs per treatment) for 14 days (phase I) then switched to a 90% concentrate diet for 2 days (phase II). In Exp. 2, lambs were fed alfalfa-brome hay (H) (six lambs), H plus 2.5% lactic acid (H2.5L) (six lambs) or H plus 5% lactic acid (H5L) (four lambs) during phase I, then switched to a 70% concentrate diet (3 days) followed by a 90% concentrate diet (10 days) (phase II). During both experiments rumen fluid samples were taken periodically for pH and lactate analyses and in vitro L- or D-lactate disappearance (IVLD) studies. Blood samples were taken to measure acid-base status, serum lactate, and serum calcium, magnesium and phosphorus. Dietary lactic acid enhanced IVLD during phase I of both experiments. L and D isomer IVLD rates were similar and followed zero-order kinetics. In Exp. 2, IVLD increased rapidly during phase II in response to increased concentrate level in the diet; the enhanced rates of H2.5L and H5L lambs were sustained for the first 3 days of phase II. Blood data from both experiments indicated a deleterious effect of dietary lactic acid on blood acid-base balance; however, this treatment effect was not manifested in any symptoms of acute acidosis. There was a decrease (P less than .05) in serum calcium during phase II of both experiments. In Experiment 1, serum calcium increased linearly (P less than .05) in response to dietary lactic acid level. In Exp. 1, rumen fluid total lactate and L-lactate were lower (P less than .05) for H5L vs H lambs during phase II. However, all lambs in Exp. 1 experienced acute acidosis; four of the nine lambs subsequently died. There was evidence of acidosis in Exp. 2, but there were no clear treatment effects during phase II on rumen fluid pH or lactate, or feed intake. All lambs adapted to the high concentrate diets as evidenced by rumen lactate levels and feed intakes. In both experiments, the proportion of L-lactate in rumen fluid decreased from almost 100 to about 50% of total lactate by the end of phase II.