1703
Monensin increases endotoxin concentration in an in vitro rumen fermentation model
Administration of antibiotics (e. g. Beta-lactam), which effect gram-negative bacteria, can lead to an increased concentration of endotoxins in the rumen. This increase can lead to endotoxin associated effects like inflammation, immune response and diseases risks, e.g. mastitis, endometritis and laminitis. Monensin has a wide range of application indications in ruminants: coccidiosis, ketosis, pulmonal edema, pneumonia, and is even used as growth promoter. This ionophore inhibits the growth of gram-positive bacteria, but there is no literature available on the effects on endotoxin release by increase of Gram-negative bacteria. The objective of this study was, therefore, to test the effect of monensin on the ruminal endotoxin concentration in an in vitro rumen fermentation model. Rumen fluid was incubated under anaerobic conditions at 39°C and a continuous flow of synthetic saliva for 336 hours. Fresh feed (50% chopped hay; 50% cereal nutrient) was supplied in nylon bags every 24 hours. Six reactors were treated with monensin (10 mg/L), the other six reactors served as untreated control. Samples of the rumen fluid were taken after 24 and 336 hours. Samples were centrifuged; heat inactivated and filtrated before dilution with endotoxin free water. Endotoxin concentration was measured with the chromogenic Limulus-Amebocyte Lysate assay, according to manufacturer’s instructions. Total bacterial count was performed with the flow cytometer. There was no significant difference in the endotoxin concentration of the control reactors (895 EU/ml) compared to the monensin treated reactors (1.715 EU/ml) after 24 hours (P > 0.05). In contrast, after 336 hours incubation, the endotoxin concentration in monensin-treated reactors (12.485 EU/ml) significantly (P < 0.05) increased compared to the control reactors (1.471 EU/ml). The total bacterial count was also significantly increased after 336 hours in the monensin-treated reactors compared to the control reactors (P < 0.05). Results of this in vitro experiment showed that monensin led to an increase of endotoxins in rumen fluid. This might be a result of the expected bacterial shift from gram-positive to gram-negative bacteria. Further investigations are necessary to verify these results and to clarify the mechanism of monensin in the in vitro rumen fermentation model. In addition, it will be useful to test other antibiotics, to avoid negative effects on bacterial populations and increase of endotoxins.
Keywords: endotoxins, monensin, rumen