Effects of subacute ruminal acidosis challenges on fermentation and biogenic amines in the rumen of dairy cows

This study was conducted to investigate if subacute ruminal acidosis (SARA) challenges result in an increase of biogenic amines in the rumen fluid and peripheral blood. Four rumen cannulated primiparous (60–140d in milk) Holstein dairy cows were assigned to two diets in a crossover experimental design. Each experimental period lasted for 21d. The diets contained (dry matter basis): 40% (COD; control) and 70% (SAID) concentrate feeds. Rumen fluid samples were collected on days 12, 15, 17 and 21 of the experimental period for measurement of pH, volatile fatty acid, ammonia-nitrogen and biogenic amine contents. Peripheral blood was also collected on days 12, 15, 17 and 21 to measure biogenic amine content. Based on adopted threshold of SARA of at least 180min/d below pH 5.8, SARA was induced by the SAID feeding. The average concentrations of tyramine (147.98 vs. 99.94μmol/L); putrescine (39.44 vs. 17.52μmol/L); histamine (161.19 vs. 46.43μmol/L); methylamine (31.81 vs. 28.09μmol/L) and tryptamine (72.25 vs. 48.77μmol/L) were higher (P<0.05) in the SAID group than in the COD in the rumen, and similar results were also observed in the peripheral blood. SAID feeding increased (P<0.05) the averages of total volatile fatty acids (from 110.83 to 125.21mmol/L), butyrate (from 11.29 to 14.53mmol/L), valerate (from 4.76 to 7.05mmol/L), and total branched-chain VFA (from 3.80 to 4.93mmol/L), and decreased (P<0.05) the ruminal pH (from 6.38 to 6.05) and acetate to propionate ratio (from 3.63 to 3.29) in the rumen. Correlation analysis showed that there were negative correlations (P<0.05) between ruminal pH and the levels of tyramine, putrescine, histamine, methylamine or tryptamine in rumen fluid or in peripheral blood. Positive correlations (P<0.05) were observed between the concentration of tyramine, putrescine, histamine and methylamine in rumen fluid and the corresponding biogenic amine in the peripheral blood during SAID feeding. In addition, the 16S rRNA gene copy number of Lactobacillus spp. was higher (P<0.05) in the SAID group than in the COD, whereas no effect was observed for the gene copy number for Streptococcus bovis. Significant positive correlations (P<0.05) were detected between the levels of ruminal tyramine, putrescine, histamine or methylamine and the number of Lactobacillus spp. In conclusion, this study showed that SARA challenges affected rumen pH, rumen fluid concentrations of total volatile fatty acids, lactate and biogenic amines, and revealed that a low rumen pH is associated with increases in rumen biogenic amine concentrations, which is accompanied by increases in plasma biogenic amine concentration.