Effects of paraquat on rumen microbial function in vitro

The toxicity of technical grade paraquat to rumen microorganisms was studied by fermentation procedures in vitro. Rumen fluid was obtained from a fistulated cow fed a diet of alfalfa hay. The herbicide was added at concentrations ranging from 0 to 1000 ppm, and incubations were conducted for 0, 12, 24 and 48 h. Digestibility of dry matter and neutral detergent fiber (NDF) and production of fatty acids were used to assess microbial function. Paraquat at the different concentrations decreased dry matter digestibility over 24 h. NDF digestibility was affected by 10, 100 and 1000 ppm over 12 and 24 h, whereas no effect was observed at 10 ppm over 48 h. Acetic acid and propionic acid productions were significantly reduced by 1000 ppm over all periods of incubations. At lower doses effects were observed after longer periods of incubation. Butyric acid production significantly increased at 1000 ppm over 12 h and decreased after 24 and 48 h of incubation. The results suggested that paraquat interferes with the digestive activity of rumen microorganisms in vitro.