EFFECT OF LASALOCID, MONENSIN AND THIOPEPTIN ON LACTATE PRODUCTION FROM IN VITRO RUMEN FERMENTATION OF STARCH

Abstract

Starch fermentations with strained rumen fluid and centrifuged rumen fluid devoid of protozoa were set up to test the effect of lasalocid, monensin, and thiopeptin on L(+) and D(−) lactate production. Protozoa-free rumen fluid was the supernatant from low-speed centrifugation of strained rumen fluid. Starch fermentation in the control (no antibiotic) with centrifuged rumen fluid resulted in higher lactate concentration than the fermentation with strained rumen fluid. Decreased lactate production with strained rumen fluid was attributed to sequestration of starch by protozoa and to enhanced lactate fermentation. Addition of lasalocid or monensin (1.5–48.0 μg mL −1 ) to the fermentation enhanced L(+) and D(−) lactate production in the presence of protozoa. In the absence of protozoa, lasalocid and monensin inhibited L(+) lactate production; however, D(−) lactate concentration was unaffected. Increased lactate production by lasalocid and monensin in the presence of protozoa was possibly due to inhibition of protozoal engulfment of starch. Thiopeptin had no effect on lactate production in the presence of protozoa but in the absence of protozoa lactate production was inhibited. Similar antibiotic responses were observed at different starch amounts (0.5, 1.5 and 3.0 g) and with starch types (soluble, corn and wheat) and with rumen fluid collected from defaunated cattle. Key words: Antibiotics, cattle, rumen, starch, fermentation, lactic acid