Ruminal Acidosis In Dairy Cows Research Articles

Challenges in the Definition and Measurement of Subacute Ruminal Acidosis in Holstein Dairy Cows: A Review

Subacute ruminal acidosis can be defined as a depression of rumen pH, which affects animal health and production. Although researchers have tried to find a solution for this disorder, it is a prevalent problem that causes considerable losses in commercial dairy cow production. This review aims to reveal critical points in current knowledge about subacute ruminal acidosis and suggest solutions for future research. The first challenging issue in subacute ruminal acidosis is the diagnosis method of this disorder, which requires appropriate statistical evaluation and modeling. In addition, biological factors should be considered to define subacute ruminal acidosis since some roles have recently been observed for different CO2 species in the rumen as a direct cause of the events. These CO2 species are sometimes more accurate than rumen pH in explaining the decrease in feed intake, milk yield, milk fat percentage, and inflammation responses. In the future, the measuring of the CO2 species in the rumen may be a replacement for pH measurement or become a factor that can greatly explain ruminal acidosis. Compared to basic methods, another challenging point is the reliability of rumen pH measurements as well as the accuracy of newly developed sensors. The reticular pH with current boluses could be measured by monitoring cows on-farm or a large number of animals in research. In conclusion, a thorough definition and precise application of new measurement devices can reveal some unknown factors for subacute ruminal acidosis in dairy cows.

High-Dose Vitamin E Supplementation Can Alleviate the Negative Effect of Subacute Ruminal Acidosis in Dairy Cows.

The aim of this trial was to assess whether the supplementation of vitamin E (VE) in high-concentrate diets could improve the fermentation and blood metabolism in the rumen of dairy cows, thereby modulating the degree of the subacute ruminal acidosis (SARA) response and improving the performance. Seven Holstein cows (four fitted with ruminal cannulas) were fed three diets (total mixed rations) during three successive periods (each lasted for 18 d): (1) the control diet (CON); (2) a high-grain (HG) diet, which was the control diet supplied with a 15% finely ground wheat diet (FGW); and (3) a high-VE diet (HGE), which was the control diet provided with a 15% FGW and 12,000 IU of VE/head per day. The results indicated that VE was able to alleviate the reduction in the dry matter intake (DMI) and milk fat yield in cows caused by HG diets. The supplementation of VE significantly reduced the levels of lipopolysaccharide (LPS), histamine (HIS), and the total volatile fatty acid (TVFA) in the rumen. The supplementation of VE observably increased the antioxidant capacity of the milk and plasma. In addition, VE markedly reduced the plasma levels of endotoxin, HIS, and pro-inflammatory factors. The supplementation of VE significantly enriched the differential metabolites of the purine metabolism, cysteine, methionine metabolism, and ABC transporter synthesis pathway in the serum. The supplementation of VE also significantly increased the relative abundance of Succiniclasticum and decreased the relative abundance of Treponema, thus reducing the production of TVFA in the rumen. In conclusion, considering that the cows in this trial had high ketone levels (BHBA > 2.3 mmol/L), we found that VE could improve the rumen fermentation and blood metabolism by modulating the relative abundance of rumen microorganisms, thereby mitigating a range of adverse effects caused by SARA.

Paraclinical Changes Occurring in Dairy Cows with Spontaneous Subacute Ruminal Acidosis under Field Conditions.

Simple SummarySubacute ruminal acidosis is a nutritional disorder that negatively impacts the health, performance, and welfare of dairy cows. This disease evolves subclinically over a long period of time, and finding suitable and easy-to-use biomarkers for early diagnosis is still a challenge for dairy practitioners. This study aimed to investigate the patterns of paraclinical changes and provide valuable data for more accurately identifying subacute ruminal acidosis under field conditions. Changes in certain blood and milk biochemical parameters were identified in this study, which, taken together, could provide a pattern of biochemical changes that would allow the easier identification of subacute ruminal acidosis in dairy cows under field conditions.This study was undertaken to investigate the changes in the blood and milk biochemical parameters found in naturally occurring and long-lasting spontaneous subacute ruminal acidosis (SARA), with the aim of identifying the patterns of paraclinical changes and providing valuable data for more accurately identifying SARA in cows under field conditions. The study was conducted on a dairy herd with a history of the occurrence of SARA-associated clinical signs. Twelve cows, between 20 and 150 days in milk, were randomly selected and subsequently subjected to venous blood, milk, and ruminal fluid collection. The mean pH value of the ruminal fluid was 5.56 ± 0.32, and 58% (7/12) of the tested cows were SARA positive (ruminal pH ≤ 5.5). The albumin, calcium, and phosphorus serum concentration values were significantly lower (p < 0.05) in the SARA group than in the group of healthy cows. Serum aspartate aminotransferase (AST) and glutamate dehydrogenase (GLDH) activity were significantly higher in the SARA cows (p < 0.05) than in the group of healthy cows. The mean values of milk fat, milk protein content, and milk fat-to-protein ratio were significantly lower (p < 0.05) in the tested cows of the SARA group than in the healthy group of cows. In conclusion, the results of the current study indicate that long-term SARA triggered by a high-concentrate diet is associated with clinically significant changes in both the blood composition (hypoalbuminemia, hypocalcemia, and increased serum AST and GLDH activity) and the milk composition (decreased fat and protein percentage and milk fat-to-protein ratio). Altogether, the obtained results provide a more reliable pattern of paraclinical changes and useful insights for detecting SARA in dairy cows under field conditions.

Comparative evaluation of the therapeutic efficacy of rumen buffers and direct fed microbials (DFM) in sub-acute ruminal acidosis in dairy cows

Sub-acute ruminal acidosis (SARA) in dairy cattle is a disorder of ruminal fermentation caused by the ingestion of large amounts of concentrates with inadequate amounts of fibre. The condition is characterized by sustained and marked decrease in rumen liquor pH ≤5.5 for at least three hours of each day. Rumen buffers and direct fed microbials (DFM) are dietary supplements that had been used in the management of SARA. Rumen liquor samples of dairy cows from the organized farms and households of Wayanad district which were at the risk of SARA were collected by rumenocentesis for rumen pH estimation. Blood samples were collected from cows positive for SARA and subjected to haemato-biochemical evaluations. Three different therapeutic protocols involving oral administration of sodium bicarbonate, Lithothamnium calcareum extracts as rumen buffers and a mixture Saccharomyces cerevisiae and Aspergillus oryzae as direct fed microbial were compared in SARA positive cows for 14 days and the efficacy of the treatment was evaluated by the improvement in rumen liquor pH after the treatment period. Rumen buffer like sodium bicarbonate was found to be more efficient than Lithothamnium calcareum and DFMs like Saccharomyces cerevisiae and Aspergillus oryzae mixture in improving the rumen pH values in cattle positive for SARA.

Models to predict the risk of subacute ruminal acidosis in dairy cows based on dietary and cow factors: A meta-analysis

The present research aimed at developing practical and feasible models to optimize feeding adequacy to maintain desired rumen pH conditions and prevent subacute ruminal acidosis (SARA) in dairy cows. We conducted 2 meta-analyses, one using data from recent published literatures (study 1) to investigate the prediction of SARA based on nutrient components and dietary physical and chemical characteristics, and another using internal data of our 5 different published experiments (study 2) to obtain adjustments based on cow status. The results of study 1 revealed that physically effective neutral detergent fiber inclusive of particles >8 mm (peNDF >8) and dietary starch [% of dry matter (DM)] were sufficient for predicting daily mean ruminal pH {y = 5.960 - (0.00781 × starch) + (0.03743 × peNDF >8) - [0.00061 × (peNDF >8 × peNDF >8)]}. The model for time of pH suppression (<5.8 for ruminal pH or <6.0 for reticular pH, min/d) can be predicted with additionally including DMI (kg/d): 124.7 + (1.7007 × DMI) + (20.9270 × starch) + (0.2959 × peNDF >8) - [0.0437 × (DMI × starch × peNDF >8)]. As a rule of thumb, when taken separately, we propose 15 to 18% peNDF >8 as a safe range for diet formulation to prevent SARA, when starch or NFC levels are within 20 to 25% and 35 to 40% ranges, respectively. At dietary starch content below 20% of DM, grain type was insignificant in affecting ruminal pH. However, increasing dietary starch contents by using corn as the sole grain source could lead to more severe drops of pH compared with using grain mix based on barley and wheat, as underlined by an interaction between starch content and grain type. Data from study 2 emphasized an increased risk of SARA for cows in the first and second lactation with lower mean pH (0.2 units) and double amounts of time at pH <5.8 compared with the cows with ≥3 parities. Given that a lower ruminal pH is expected in these high-risk cows, it is advisable to keep the lower end of recommended starch (20%) and higher peNDF >8 (18%) contents in the diet of these cows. Overall, the present study underlines the possibility of predicting SARA based on dietary factors including peNDF >8 and starch contents, as well as DMI of the cows, which can be practically implemented for optimal diet formulation for dairy cows. With more data available, future studies should attempt to improve the predictions by including additional key dietary and cow factors in the models.

Short-term screening of multiple phytogenic compounds for their potential to modulate chewing behavior, ruminal fermentation profile, and pH in cattle fed grain-rich diets

In cattle, proper rumen functioning and digestion are intimately linked to chewing behavior. Yet, high grain feeding impairs chewing activity, increasing the risk of subacute ruminal acidosis and dysfermentation. This study aimed to screen 9 different phytogenic compounds for their potential to modulate chewing activity, meal size, rumino-reticular short-chain fatty acids (SCFA), and pH during consumption in a first daily meal and shortly thereafter in cattle fed a grain-rich diet. Treatments were control (total mixed ration without phytogenic) or addition of a phytogenic compound at a low or high dose. Phytogenic compounds and doses (all in mg/kg) were angelica root (6.6 and 66), capsaicin (10 and 100), gentian root (6.6 and 66), garlic oil (0.3 and 3), ginger extract (40 and 400), L-menthol (6.7 and 67), mint oil (15.3 and 153), thyme oil (9.4 and 94), and thymol (5 and 50), for the low and high groups, respectively. Before the start of the screening experiment, cows were fed to reach subacute ruminal acidosis conditions, confirmed with the time of ruminal pH <5.8 being 655 ± 148.2 min/d. During the screening experiment, the treatments were offered in a controlled meal (2.5 kg of DM for 4 h) as part of the daily diet with 65% concentrate. Each treatment was tested in 4 of the 9 cannulated Holstein cows using an incomplete Latin square design. Ruminal and reticular fluids were sampled before and after each treatment, and data collected before the meal were used as covariates. Chewing and ruminal pH were monitored during the treatment, followed by 2 h of complete feed restriction, and then 4 h of ad libitum feed intake without phytogenic. Data showed that supplementation of angelica root tended to linearly increase rumination time immediately after the first meal when feed was restricted (27.3, 41.9, and 42.6 ± 5.99 min for control, low and high groups, respectively). Capsaicin increased eating time (43.6, 49.4, and 66.4 ± 4.93 min) during consumption but did not affect ruminal total SCFA or mean ruminal pH. Garlic oil reduced the concentration of reticular total SCFA (75.7, 71.3, and 60.1 mM) and tended to decrease ruminal acetate-to-propionate ratio (2.50, 1.78, and 1.87 ± 0.177) with no effect on ruminal pH. The L-menthol affected reticular total SCFA quadratically (76.1, 64.9, and 81.0 ± 4.22%), and ruminal pH responded quadratically when feed was reintroduced ad libitum (6.0, 6.3, and 6.1 ± 0.07). Mint oil did not affect chewing or total SCFA during consumption, but the low dose increased ruminal pH (6.5, 6.7, and 6.5 ± 0.08). Thyme oil tended to lower the severity of ruminal acidosis. Overall, phytogenic compounds demonstrated distinct dose-dependent effects to beneficially influence chewing behavior, modulate fermentation, and mitigate ruminal acidosis in dairy cows under a high-grain challenge diet.

Sub-acute ruminal acidosis in dairy cows: Its causes, consequences and preventive measures

Sub-acute ruminal acidosis in dairy cows: Its causes, consequences and preventive measures

Non-Invasive Indicators Associated with Subacute Ruminal Acidosis in Dairy Cows

Abstract The aim of the study was to characterize the interrelationship between decreased ruminal fluid pH during subacute ruminal acidosis (SARA) and concentrations of principal constituents of milk and biochemical indices associated with nitrogen utilizations such as rumen ammonia nitrogen (RAN), blood urea nitrogen (BUN) and milk urea nitrogen (MUN). Ruminal fluid samples were obtained by rumenocentesis from 305 cows representing 13 dairy herds. The cows were divided according to ruminal fluid pH into three groups: low, moderate, and high rumen pH cows. The herds were divided into three groups on the basis of the percentages of cows with an assigned value of ruminal fluid pH: SARA-positive, SARA-risk and SARA-negative. SARA-positive herds were characterized by higher concentrations of RAN (12.6 vs. 6.9 mg/dL), BUN (16.2 vs. 10.1 mg/dL) and MUN (12.4 vs. 9.1 mg/dL) compared to SARA-negative herds. Similarly, low-rumen pH cows had greater concentrations of RAN, BUN and MUN than high-rumen pH cows (11.9 vs. 5.8 mg/ dL, 19.9 vs. 14.1 mg/dL, and 12.3 vs. 9.5 mg/dL, respectively). Moreover, SARA-positive herds and low-rumen pH cows had the highest lactose and the lowest fat concentrations in milk. The study demonstrated that the concentration of milk urea nitrogen could be considered one of the indirect and non-invasive indicators of the occurrence of subacute ruminal acidosis in dairy herds.

Feeding of bakery by-products in the replacement of grains enhanced milk performance, modulated blood metabolic profile, and lowered the risk of rumen acidosis in dairy cows

Leftover bakery by-products (BP) from bakeries and supermarkets may serve as energy-rich ingredient in ruminant diets. The aim of the present study was to evaluate the effect of the successive substitution of cereal grains by BP on dry matter (DM) intake, milk production, and metabolic health as well as ruminal pH and eating and chewing behavior of dairy cows. Twenty-four lactating Simmental cows (149 ± 22.3 d in milk, lactation number 2.63 ± 1.38, 756 ± 89.6 kg of initial body weight) were fed a total mixed ration containing a 50:50 ratio of forage to concentrate throughout the experiment (35 d). During the first week, all cows received a control diet (without BP) as a baseline (d -7 to 0). In the next 4 wk (d 1 to 28), cows were allocated to 3 groups differing in the BP concentrations of diets [0% BP (CON), 15% BP, and 30% BP on a DM basis]. The DM intake and reticuloruminal pH were continuously measured. Blood and milk samples were taken every week, but only results from the experimental period (d 21 and 28) were used for statistical analyses, whereas results from the baseline were considered covariates. Diet analyses showed that BP inclusion increased the ether extract and sugar contents, whereby starch and neutral detergent fiber decreased. Experimental data showed that feeding BP in the diet increased DM intake. Furthermore, the cows fed 30% BP produced roughly 4 kg/d more milk and energy-corrected milk than the CON cows. The milk urea nitrogen was lower in cows fed the BP. Feeding BP reduced the blood glucose and insulin concentrations, whereas nonesterified fatty acids, β-hydroxybutyrate, and cholesterol increased linearly. Cows fed 15% BP had the shortest period of time in which ruminal pH was below 5.8, in contrast to CON cows (+188 min/d). Taken together, the results suggest that the inclusion of up to 30% BP in the diets of mid-lactation dairy cows shifted the nutrient profile from a glucogenic diet to a lipogenic diet, holding the potential to enhance performance and lower the risk of subacute ruminal acidosis in dairy cows.

Subacute ruminal acidosis in dairy cows - physiological background, risk factors and diagnostic methods

According to the latest studies, the prevalence of subacute ruminal acidosis (SARA) is around 20% in early and mid- lactation dairy cows, generating annual losses in the United States of approximately USD 500 million to 1 billion. The diagnosis of SARA is still difficult due to lack of pathognomonic clues and the delayed appearance of certain clinical signs. Therefore, SARA remains neglected or even unrecognized in many dairy herds. SARA is characterized by daily episodes of low ruminal pH, when the pH remains in the range of 5.2 to 6 for a prolonged period due to the accumulation of short-chain fatty acids and insufficient rumen buffering. The causes of SARA are related to high-grain diets, such as feeding excessive amounts of non-structural carbohydrates and highly fermentable forages, and insufficient dietary coarse fibre. SARA is associated with the inflammation of several organs and tissues in dairy cows, and its main long-term health and economic consequences are the fluctuation of feed intake, reduced fibre digestion, depression of milk yield and milk fat content, gastrointestinal damage, diarrhoea, laminitis, liver abscesses, and lameness. The aim of this review is to summarize the information available on the physiological aspects, risk factors, prevalence and possible indicators of SARA in dairy cattle. Basedon the existing literature, rumenocentesis and the use of an oral stomach tube are reliable field techniques to detect SARA. Nowadays, improved field techniques allowing the continuous measurement of reticuloruminal pH are also available for better diagnosis of SARA. Wireless indwelling pH probes may become important tools for the continuous measurement of ruminal pH in the coming years.

The economic value of information provided by milk biomarkers under different scenarios: Case-study of an ex-ante analysis of fat-to-protein ratio and fatty acid profile to detect subacute ruminal acidosis in dairy cows

Monitoring systems (MS) provide additional information that many developers and researchers expect will reduce the uncertainty surrounding decision-making in livestock production and therefore enhance management decisions. However, the actual economic value of the information (VoI) yielded by MS has hardly been investigated. The aim of this study was to fill that void based on two objectives. The first is to estimate the VoI of MS prior to implementation using decision analysis based on scarce data from different sources. The second objective is to identify which factors most influence the VoI of MS and to develop recommendations about the focus of future MS development. To illustrate our objectives, we used a case study of two milk biomarkers used to monitor subacute ruminal acidosis (SARA) in dairy cows: fat-to-protein ratio (FPR) and the fatty acid profile (FAP). FPR is presently used to monitor SARA, while FAP is a newly developed test, currently in the pre-commercial phase, with reports of better accuracy than FPR. A stochastic decision tree model was used to estimate the expected monetary value of three levels of information with regards to SARA: (i) no monitoring, monitoring (ii) with FPR or (iii) with FAP. The VoI of FPR and FAP were calculated as the difference in expected monetary value of monitoring with FPR and FAP as compared with no monitoring, respectively. Several scenarios were modeled using sensitivity and elasticity analyses. The aim was not only to compensate for the scarcity of data for some variables, but also to identify under which conditions decisions based on FAP monitoring were indeed the best. In all the scenarios, monitoring SARA with FPR had the lowest expected monetary value. No monitoring was a better decision in 70% of the iterations in the scenario that described the most probable situation. The VoI of FAP was positive when SARA prevalence was between 0.21 and 0.79 with its maximum value at 0.61, when the treatment costs were lower than €116/case/year and when the disease costs were higher than €260/case/year. Moreover, an increase of specificity of the FAP to 0.95 yielded a positive VoI, whereas an increase of its sensitivity to 1.0 still yielded a negative VoI, suggesting that developers of the FAP should focus on improving its specificity rather than its sensitivity. To avoid suboptimal use of finite resources while developing MS, we recommend ex-ante investigation of the VoI of the MS under development.

A cow-level association of ruminal pH on body condition score, serum beta-hydroxybutyrate and postpartum disorders in Thai dairy cattle.

Subacute ruminal acidosis in dairy cows occurs when ruminal pH is below about 5.5. However, the exact threshold level of ruminal pH affecting cow health is still in debate. This investigation was carried out in 505 cows within 31 farms. The postpartum disorders, including dystocia, retained placenta, anestrus, cystic ovary, metritis, clinical mastitis and lameness, were analyzed. Ruminal pH, serum beta-hydroxy butyrate (SBHB), serum urea nitrogen and body condition score (BCS) were measured once during the 3 to 6 weeks postpartum, while BCS was determined once more at 1 week before calving. Ruminal pH was determined by ruminocentesis technique. The ruminal pH was evaluated to study the association with BCS, SBHB and postpartum disorders using linear regression in a generalized linear mixed model with farm as a random effect. The results show that low ruminal pH was associated with dystocia, metritis and lameness. Moreover, a low ruminal pH can be found in cows with a high loss of BCS after calving and also in cows with low SBHB postpartum. These findings confirmed the feasibility of the ruminocentesis technique and the association of low ruminal pH on various postpartum disorders at the individual cow level. However, the consequences of low ruminal pH on dairy cow health still needs more exploration for a better understanding of the physiological mechanisms.

Ruminal acidosis in dairy cows

WE would like to report an unusual outbreak of ruminal acidosis in freshly calved dairy cows. The affected herd of 200 cows is located in south Ayrshire and experienced four similar cases over a period of 10 days. All four cases had appeared well before calving and had been in a calving pen for a few consecutive nights where a camera allowed for easy observation. The calving pen did not have a water trough although some buckets of water would be brought to this area. During the day these …

Evaluation of diagnostic measures for subacute ruminal acidosis in dairy cows

Li, S., Gozho, G. N., Gakhar, N., Khafipour, E., Krause, D. O. and Plaizier, J. C. 2012. Evaluation of diagnostic measures for subacute ruminal acidosis in dairy cows. Can J. Anim. Sci. 92: 353–364. Effects of subacute ruminal acidosis (SARA) challenges on measurements of feces, urine, milk and blood samples, and of feeding behavior were investigated to determine which of these measurements may aid in the diagnosis of SARA. Eight multiparous lactating dairy cows were used in a crossover design with two 6-wk experimental periods. During weeks 1, 2, and 6, cows received a control diet with a forage-to-concentrate ratio of 58:42. During weeks 3 to wk 5, a grain-based SARA challenge (GBSC) or an alfalfa-pellet SARA challenge (APSC) was conducted by replacing 12% of the dry matter of the control ration with pellets containing 50% ground wheat and 50% ground barley, and by replacing 26% of the dry matter of the control ration with pellets of ground alfalfa, respectively. The rumen pH depression did not differ between the challenges. The GBSC increased the concentrations of lipopolysaccharide (LPS) in feces and of serum amyloid A in blood, but decreased that of milk fat and urea in blood. The APSC increased the urine pH, the net-acid-base excretion, and the red blood cell count and potassium concentration in blood. Both challenges increased the concentrations of LPS and propionate in rumen fluid, protein in milk, glucose, lactate and sodium and the partial pressure of CO2in blood, and tended to decrease the concentration of chloride in blood. The measures that were similarly affected by both challenges may aid in the diagnosis of a rumen pH depression. Differences between the SARA challenges suggest that this disorder is not solely rumen pH dependent.

Haematological Indicators Affected by the Subacute Ruminal Acidosis in Dairy Cows

Haematological Indicators Affected by the Subacute Ruminal Acidosis in Dairy Cows

Comparative Efficacy of Combination of Buffer Treatments in Sub Acute Ruminal Acidosis in Dairy Cows

The present study was conducted to evaluate the effect of buffer treatments on ruminal physical parameters, clinical scoring, production parameters and blood gas parameters in subacute ruminal acidosis in dairy cattle. Rumen fluid examination was carried out by rumenocentesis and rumen fluid was examined for pH (physical and chemical parameters). Production parameters and rumen scores of SARA positive animals were also studied. Haemtobiochemical parameters of SARA positive animals were analyzed with blood gas analyzer. Additionally, SARA positive animals were treated with sodabicarbonate and combination of HSCAS (Hydrated sodium calcium aluminosilicates), sodium salt of carbonic acid + oxide of magnesium. The above studies suggested that combination of Hydrated Sodium Calcium Aluminosilicates and sodium salt of carbonic acid proves to be beneficial in the early restoration of rumen pH (physical and chemical parameters), rumen scores, milk yield, milk fat% and DMI than sodium bicarbonate alone. Heamatobiochemical parameters of SARA positive animals showed no significant change from 0 h (pre-treatment) and 96 h (Post- treatment).

Serum Alkaline Phosphatase and Amylase Activities in Subacute Ruminal Acidosis in Dairy Cows

The small meshed purse seine net without pocket was locally called ‘ghan’ in Ratnagiri because of smaller mesh size of the main webbing of the net. The study deals specifically with the design, construction and operational details of the small meshed purse seine nets (ghan) without pocket operated from Ratnagiri. The nets were made of polyamide (PA) with knotted netting having small mesh size of 30 mm. The total length and stretched depth of purse seines in Ratnagiri was 521.5 to 1112.4 m and 33 to 82.35 m, respectively. The hanging coefficient along the floatline was 0.52 to 0.88 while along the lead line was 0.59 to 0.95. The gear was operated using the single boat with the aid of an unpowered skiff. The depth of operation was always less than the depth of the net. The time required for setting, pursing, hauling and brailing varied from two to two and half hours.

Alfalfa pellet-induced subacute ruminal acidosis in dairy cows increases bacterial endotoxin in the rumen without causing inflammation

A study was conducted to determine if subacute ruminal acidosis (SARA) induced by feeding alfalfa pellets results in increases in free bacterial lipopolysaccharide (LPS) in rumen fluid and peripheral blood, and acute phase proteins in plasma, and to determine the effect of alfalfa pellet-induced SARA on feed intake, rumen fermentation characteristics, milk production and composition, and blood metabolites. Eight lactating Holstein cows, 4 of which were ruminally cannulated, were used in a 6-wk experiment and were fed once daily at 0900h. During wk 1, cows received a diet containing 50% of DM as concentrate and 50% of DM chopped alfalfa hay. Between wk 2 and wk 6, alfalfa hay was gradually replaced with alfalfa pellets at the rate of 8% per week to reduce rumen pH. Rumen pH was monitored continuously in the ruminally cannulated cows using indwelling pH probes. Rumen fluid and peripheral blood were sampled 15min before feed delivery and at 6h after feed delivery. Based on adopted threshold of SARA of at least 180 min/d below pH 5.6, SARA was induced from wk 3 onwards. Replacing 40% of alfalfa hay with alfalfa pellets quadratically increased the DMI from 18.1kg/d in wk 1 to 23.4kg/d in wk 6. This replacement linearly decreased milk yield (32.7 vs. 35.9kg/d) and milk fat percentage and yield (2.32 vs. 3.22%, and 0.77 vs. 1.14kg/d, respectively), but increased milk protein percentage and yield (3.80 vs. 3.04%, and 1.23 vs. 1.07kg/d, respectively). This gradual replacement also linearly increased the daily averages of total volatile fatty acids (90 to 121.9mM), acetate (53.9 to 66.8mM), propionate (21.5 to 39.6mM), and osmolality (277.7 to 293.8 mmol/kg) in the rumen and decreased the acetate to propionate ratio from 2.62 to 1.73. Replacing alfalfa hay with alfalfa pellets linearly increased blood lactate from 1.00mM in wk 1 to a peak of 3.46mM in wk 5. Induction of SARA in this study increased free rumen LPS concentration from 42,122 endotoxin unit (EU)/mL in wk 1 to 145,593 EU/mL in wk 6. However, this increase was not accompanied by an increase in LPS (<0.05 EU/mL) and in acute phase proteins serum amyloid-A, haptoglobin, and LPS-binding protein in peripheral circulation. Results suggest that SARA induced by alfalfa pellets increased LPS in the rumen without causing translocation of LPS and an immune response.

Subacute ruminal acidosis in dairy cows: The physiological causes, incidence and consequences

During subacute ruminal acidosis (SARA) rumen pH is depressed for several hours per day due to accumulation of volatile fatty acids and insufficient rumen buffering. Surveys suggested an incidence of SARA of between 19% and 26% in early and mid-lactation dairy cows. Causes of SARA include feeding excessive amounts of non-structural carbohydrates and highly fermentable forages, and insufficient dietary coarse fiber. Consequences of SARA include feed intake depression, reduced fiber digestion, milk fat depression, diarrhea, laminitis, liver abscesses, increased production of bacterial endotoxin and inflammation characterized by increases in acute phase proteins. The increase in endotoxin is similar among methods for SARA induction, but depends on the diet fed before induction. Increases in acute phase proteins vary among methods of SARA induction, even when the methods result in similar rumen pH depressions. This suggests that the inflammatory response might not be solely due to bacterial endotoxin in the rumen.

Ruminal Lipopolysaccharide Concentration and Inflammatory Response During Grain-Induced Subacute Ruminal Acidosis in Dairy Cows

The effects of grain-induced subacute ruminal acidosis (SARA) in lactating dairy cows on free ruminal lipopolysaccharide (LPS) and indicators of inflammation were determined. Four mid lactation dairy cows were divided into 2 groups of 2 cows and used in a repeated switchover design. During each period, SARA was induced in 2 animals for 5 subsequent days by replacing 25% of their total mixed ration (dry matter basis) with a concentrate made of 50% wheat and 50% barley. The other 2 cows acted as controls and were fed a total mixed ration diet in which 44% of dry matter was concentrate. On average, inducing SARA did not affect milk composition, increased the duration of rumen pH below 5.6 from 187 to 309 min/d, and increased free ruminal LPS concentration from 24,547 endotoxin units (EU)/mL to 128,825 EU/mL. Averaged across treatments, milk fat yield and milk protein yield were 0.66 and 1.00kg/d, respectively. Rumen pH and milk fat data suggest that control cows also experienced ruminal acidosis, albeit a milder form of this disease than SARA cows. Serum LPS concentration in both control and SARA cows was less than the detection limit of <0.01 EU/mL for the assay. Induction of SARA elevated serum amyloid A concentration from 286.8 to 498.8μg/mL, but did not affect other markers of inflammation including haptoglobin, fibrinogen, serum copper, or white blood cells. These results suggest that grain-induced SARA in mid lactation dairy cows increases the lysis of gram-negative bacteria and activates an inflammatory response.