Ruminal lactic acidosis: relationship of forestomach motility to nondissociated volatile fatty acids levels.

Ruminal lactic acidosis was produced in 9 overnight fasted rumen-fistulated sheep by placing ground wheat (40 g/kg of body weight) into the rumen. Ruminal stasis occurred within 8 hours of grain engorgement in 6 sheep (early stasis group) and between 10 and 12 hours in the remaining 3 sheep (late stasis group). The initial impairment to forestomach motility was a decrease in the mean frequency of reticulo-ruminal contractions which occurred within 4 hours of the intraruminal placement of wheat in the early stasis group and within 6 hours in the late stasis group. Since blood pH, carbon dioxide pressure, and serum bicarbonate were all normal, systemic acidosis was not a contributing factor to this decrease in contraction frequency. The concentrations of total nondissociated volatile fatty acids (VFA; acetic, propionic, and butyric acid) in ruminal fluid, however, were significantly increased, being 13.60 mM/L (mean, pH 4.92) in the early stasis group and 15.77 mM/L (pH 4.80) in the late stasis group. Free DL-lactic acid in ruminal fluids was 6.37 +/- 6.1 mM/L (mean +/- SD) in the early stasis group and 9.72 +/- 4.2 mM/L in the late stasis group. A reduction in contraction amplitude was observed within 6 hours of grain engorgement in the early stasis group and within 8 hours in the late stasis group. At these times, the concentrations of nondissociated VFA were 10.19 mM/L (pH 4.46) in the early stasis group and 10.52 mM/L (pH 4.62) in the late stasis group. The ruminal values of free DL-lactic acid were 13.93 mM/L in the early stasis group and 16.14 mM/L in the late stasis group.(ABSTRACT TRUNCATED AT 250 WORDS)