Subacute ruminal acidosis affects fermentation and endotoxin concentration in the rumen and relative expression of the CD14/TLR4/MD2 genes involved in lipopolysaccharide systemic immune response in dairy cows.

The first objective of this study was to investigate the effects of subacute ruminal acidosis (SARA) on fermentation, ruminal free lipopolysaccharides (LPS), and expression of the cluster of differentiation 14 (CD14), toll-like receptor 4 (TLR4), and myeloid differentiation protein 2 (MD2) complex in white blood cells involved in the systemic immune response in dairy cows. The second objective was a study of whether increased expression of the LPS receptor complex led to increases in the concentrations of plasma high-density lipoprotein (HDL) and serum Ca. Three hundred five dairy cows located in 13 Polish high-yielding dairy commercial farms were selected according to their days in milk (40-150 d; average = 75), 305-d milk yield (10,070-12,041 kg; average = 10,940), and number of lactations (primiparous, n = 139 and multiparous, n = 166). Next, the herds were segregated into 3 groups based on the percentages of cows with an assigned value of ruminal fluid pH: SARA-positive, SARA-risk, and SARA-negative herds. Moreover, 305 selected dairy cows were divided according to the classification based on ruminal fluid pH into 3 groups as healthy (pH >5.81), risk (pH 5.8-5.6) and acidotic cows (pH <5.6). Rumen fluid samples were collected via rumenocentesis. In the AC group, we recorded higher concentrations of ruminal free LPS [4.57 Log10 endotoxin units (EU)/mL; 42,206 EU/mL] compared with the healthy group (4.48 Log10 EU/mL; 34,179 EU/mL). Similarly, the concentration of ruminal free LPS was higher in SARA-positive herds (4.60 Log10 EU/mL; 43,000 EU/mL) compared with SARA-negative herds (4.47 Log10 EU/mL; 32,225 EU/mL). The relative mRNA abundance of genes associated with the function of LPS receptors, such as CD14, TLR4, and MD2, in white blood cells differed between all experimental groups on both cow and herd levels. In the acidotic group, we recorded higher concentrations of HDL (78.16 vs. 68.32 mg/dL) and serum amyloid A (10.80 vs. 9.16 µg/mL) and lower concentrations of Ca (8.26 vs. 10.16 mg/dL) and haptoglobin (470.19 vs. 516.85 ng/mL) compared with the healthy group. Similar results were obtained in the SARA herd status analysis, but the concentration of lipopolysaccharide-binding protein differed statistically. Moreover, the pH of ruminal fluid was negatively correlated with relative mRNA abundance of genes such as CD14, TLR4, MD2, and concentrations of serum HDL and serum amyloid A, although positively correlated with serum Ca. The results indicated that decreases in ruminal fluid pH increased the release of free LPS into the rumen and stimulated the expression of the LPS receptor complex and immune response. Moreover, an increase in the expression of the LPS receptor led to higher concentrations of plasma HDL and lower serum Ca, which may be a protective mechanism against endotoxemia. However, the biological significance of these results needs to be investigated further in larger field trials.

Relationship between pH of ruminal fluid during subacute ruminal acidosis and physiological response of the Polish Holstein-Friesian dairy cows.

The aim of the study was to investigate the effect of ruminal fluid pH depression on biochemical indices of blood, urine, feces, and milk, and to determine which of them may be helpful as a marker for the diagnosis of subacute ruminal acidosis (SARA). Ruminal fluid samples were obtained by rumenocentesis from 305 cows representing 13 commercial dairy herds. The herds were selected based on percentages of cows with an assigned value of ruminal fluid pH segregated into three groups as: SARA-positive herd, if at least 25% of the ruminal fluid samples indicated a pH < 5.6; SARA-risk herd, if less than 25% of ruminal fluid samples indicated a pH < 5.6, but at least 33% showed a pH ≤ 5.8; and SARA-negative herd, if less than 25% of the ruminal fluid samples indicated a pH < 5.6, but less than 33% exhibited a pH = 5.8. Moreover, the dairy cows were divided according to the ruminal fluid pH into three groups as follows: healthy cows (HC, pH>5.80, n = 196), risk cows (RC, pH 5.8 - 5.6, n = 51), and acidotic cows (AC, pH < 5.6, n = 58). Almost 19% (58/305) of the cows were classified as acidotic (pH < 5.6) and 46.2% of the herds as SARA-positive. In the AC group, higher concentrations of insulin-like growth factor-I (IGF-I), non-esterified fatty acids (NEFA), rectal temperature and lower blood pH, compared with those of the HC group, were recorded. Moreover, in the SARA-positive herds, higher concentrations of IGF-I and the lowest blood pH, compared with SARA-negative herds, were observed. The lowering of ruminal fluid pH increased the blood IGF-I and NEFA concentrations and the rectal temperature and decreased the blood pH. These measures are indicators of the physiological changes that occur as part of the pathogenesis of the condition and may be helpful for the diagnosis of the SARA syndrome when serial measurements are conducted.