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Summary: Controlling rumen disorders is critical to ensure successful dairy herd health management. Lactation diets of dairy cows are commonly rich in concentrates and low in physically effective fibre. Feeding of these diets increases the risk of rumen disorders with far‐reaching consequences for cattle health, welfare and sustainability of dairy production. The term subacute ruminal acidosis or SARA is often used as a synonym for poor rumen health. Being subclinical, SARA lacks of clear symptoms and is therefore difficult to diagnose and to control in the practice. This review article summarises common and identifies new direct and indirect cow signals related to SARA. We have performed a scientific evaluation and interpretation of each of these cow signals by highlighting their advantages and disadvantages from the practitioner's point of view. The gold standard of SARA cow signals still remains direct measurement of ruminal pH. However, continuous pH monitoring is cost‐intensive and often biased by sensor drift. Single‐point ruminal pH measurements by oral stomach tubing or rumenocentesis have strong limitations. Therefore, there is a need for reliable and robust markers of SARA that are easily accessible and inexpensive. Such indirect parameters are the observation of chewing and feeding activities, as well as the monitoring of milk, faecal, urine and blood variables. Also, novel technologies that allow rapid and non‐invasive measurement of the rumen mucosa thickness and ruminal motility patterns might provide advantages in SARA diagnosis. Due to several constraints of these indirect diagnostic tools, such as limited specificity and sensitivity, we strongly recommend using a combination of the signals to reliably identify cows at risk of SARA in a dairy herd. [ABSTRACT FROM AUTHOR]

Feeding of high-concentrate diets to cattle increases the risk of subacute ruminal acidosis (SARA). Indwelling wireless pH sensors have become popular as an early diagnostic tool for SARA recently. However, the recommended pH thresholds of SARA derive from measurements taken from free-rumen liquid (FRL) in the ventral rumen, and not from the reticulum, where the mentioned sensors are located. The aim of this study was to evaluate commercially available indwelling pH boli for the accuracy and precision in predicting ruminal pH of FRL and the particle-associated rumen liquid (PARL) under varying dietary concentrate levels. An additional aim was to define SARA pH thresholds of indwelled pH boli, which can be used for SARA diagnostics. The experiment was conducted with eight nonlactating rumen cannulated Holstein cows fed 0% or 65% concentrate. Data showed that the mean pH of indwelled boli was consistently higher than in FRL and PARL (pH 6.62 ± 0.02, 6.43 ± 0.02 and 6.18 ±0.02, respectively) across feeding regimens. Interestingly, the diurnal differences in pH among indwelled boli, FRL and PARL became greater during concentrate feeding, especially at 8 h after the morning feeding, suggesting that with high-concentrate diets a particular adjustment of reticular sensor pH vs. ruminal pH in FRL and PARL is needed. The concordance correlation coefficient analysis, representing the reproducibility of the bolus measurements, was high for bolus-FRL (0.733) and moderate for bolus-PARL (0.510) associations. Furthermore, the quantitative relationship of the pH in FRL and PARL to the pH of the boli was described by linear regression analysis. The study determined that the common SARA threshold of pH 5.8 in FRL corresponds to a bolus pH of 6.0. [ABSTRACT FROM AUTHOR]

Aims: To evaluate the effects of treating barley grain with lactic acid (LA) and heat on postprandial dynamics of 19 microbial taxa and fermentation in the rumen of dairy cows. Methods and Results: This study was designed as a double 3 9 3 Latin square with six rumen-cannulated cows and three diets either containing untreated control barley or barley treated with 1% LA and 1% LA and heat (LAH, 55°C). Microbial populations, pH and volatile fatty acids were assessed in rumen liquid and solids during the postprandial period. Propionate increased and butyrate decreased in rumen solids of cows fed LA and LAH treated barley compared to the control barley. The LA but not LAH treatment depressed Fibrobacter succinogenes in rumen liquid and solids, whereas the opposite effect was observed for Ruminococcus albus in both fractions and Ruminococcus flavefaciens in rumen solids. LA promoted Ruminobacter amylophilus with the effect being more pronounced with LAH. The Lactobacillus group and Megasphaera elsdenii increased in both fractions with LA but not with LAH. Conclusions: LA and LAH treatment of barley differently altered ruminal abundance of certain bacterial taxa and fungi and increased propionate fermentation in rumen solids, whereby LA and LAH effects were consistent and mostly independent of the rumen fraction and time after barley feeding. Significance and Impact of the Study: Results provided evidence that LA and LAH treatment of barley can enhance rumen propionate fermentation without adversely affecting rumen pH. As propionate is the major contributor to gluconeogenesis in ruminants, the present barley treatment may have practical application to enhance energy supply in dairy cows. [ABSTRACT FROM AUTHOR]

The objective of this investigation was to determine associations among rumen endotoxin, plasma serum aniyloid A (SAA), and C-reactive protein (CRP) with plasma Ca, Fe, Zn, and Cu in lactating cows challenged with graded amounts of rolled barley grain in the diet (i.e., 0, 15, 30, and 45% of DM1). Correlative relationships among variables were determined by linear and nonlinear regression procedures adjusted for the effects of day, animal, and experimental period. Increasing the amount of grain in the diet was successful in inducing an acute phase response, as assessed by augmentation of rumen endotoxin and plasma CRP and SAA (P < 0.01). The correlative analysis revealed inverse, nonlinear relationships of rumen endotoxin and plasma SAA with circulating Ca. Interestingly, plasma Ca reached the asymptotic plateau at 10.6 rng/dL. The increase in rurnen endotoxin was associated with an abrupt decrease in plasma Fe (R² = 0.91; P < 0.001). A similar relationship, although at a reduced estimation accuracy (R² = 0.21; P < 0.01), was observed between rumen endotoxin and plasma Zn. Augmentation of rumen endotoxin and plasma CRP resulted in a positive, biphasic response of plasma Cu. In conclusion, the increase in rumen endotoxin in response to high-grain diets, and the resulting increases in plasma SAA and CRP, were strongly correlated with fluctuations of plasma minerals. Results suggest that new feeding strategies should be developed to curb the release of endotoxin in the rumen fluid to prevent perturbing minerals in the plasma. [ABSTRACT FROM AUTHOR]