Starch source in high concentrate rations does not affect rumen pH, histamine and lipopolysaccharide concentrations in dairy cows

The replacement of ground corn by cassava meal on rumen pH, lipopolysaccharide (LPS) and histamine concentrations under typical Thai feeding conditions (high concentrate diets and rice straw as the sole source of roughage) was investigated. Four rumen-fistulated crossbred Holstein, non-pregnant, dry cows were randomly assigned to the four experimental rations in a 4×4 Latin square design with 21-d periods. Each period consisted of a 14-d run-in/wash out period, followed by a 7-d experimental period. During the run-in/wash out period, the cows were offered 5.4 kg DM of concentrate containing 4.6% cassava meal and rice straw was provided ad libitum. During the 7 day of each experimental period, cows were offered 10.5 kg DM of concentrate containing either 4.6% or 18.3% or 32.4% or 46.2% cassava meal and 1.5 kg of rice straw. Irrespective of dietary treatments, rumen total VFA and lactate concentrations were significantly affected by sampling day, which were significantly higher on day 1 versus days 3 and 7 of the experimental periods. Mean postprandial rumen pH was reduced to values <5.6 for at least 6 h on days 3 and 7 of each experimental period. However, the relationship between rumen pH, total VFA and lactate concentrations was not straight forward. Rumen LPS and histamine concentrations were not affected by either ground corn or cassava mean, but values significantly increased from day 1 to 7 of each experimental period with the values ranging from 10.3×103 to 40.3×103 EU/ml and 11.5 to 33.2 μM, respectively. Both plasma LPS and histamine concentrations were below the detection limit. It can be concluded that the amount of concentrate but not the replacement of ground corn by cassava meal, affect rumen pH, rumen fluid concentrations of total volatile fatty acids, lactate, histamine and LPS. Irrespective of the dietary treatments, the results suggested that a low rumen pH is associated with an increase in rumen histamine and LPS concentration, which is not accompanied by an increase in plasma histamine or LPS concentration.