METABOLIC VARIABLES AFFECTING THE EFFICACY, SAFETY, AND FATE OF AGRICULTURAL CHEMICALS
Location: Animal Metabolism-Agricultural Chemicals Research
Title: The in vitro reduction of sodium [36Cl]-chlorate in bovine ruminal fluid
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 26, 2007
Publication Date: July 1, 2007
Citation: Oliver, C.E., Bauer, M.L., Caton, J.S., Anderson, R.C., Smith, D.J. 2007. The in vitro reduction of sodium [36Cl]-chlorate in bovine ruminal fluid. Journal of Animal Science 85:2059-2068.
Interpretive Summary: An experimental chlorate product has been shown to reduce the number of human pathogenic bacteria such as E. coli O157:H7 and Salmonella enterica in gastrointestinal tracts of food animals, including cattle. In a previous study we determined that only a small fraction of an oral dose of chlorate is present in fecal and gastrointestinal material of cattle slaughtered 24 hours after their last exposure to chlorate. A great amount of the dosed chlorate was metabolized to chloride ion, a naturally occurring compound that is actually vital to life. Because biotransformation of chlorate to chloride represents a pathway in which chlorate becomes unavailable to act upon gastrointestinal pathogens, this study was conducted to determine the extent of chlorate transformation to chloride by ruminal microorganisms and to determine whether diet composition effects chlorate transformation. We found that chlorate is transformed to chloride ion by ruminal microorganisms, but that diet type did not affect the rate at which this conversion took place. Data generated from this study are useful in understanding the mode of chlorate action in ruminant animals and in understanding the mechanism through which chlorate is deactivated in live animals.
Sodium chlorate effectively reduces or eliminates the numbers of gram-negative pathogenic bacteria in the gastrointestinal tracts of live cattle. Limitations to the in vivo efficacy of chlorate are its rapid absorption from the gastrointestinal tract and its presumed reduction to chloride within the gastrointestinal tract. We hypothesized that chlorate would be reduced via ruminal bacteria in a ruminal in vitro system, and that the reduction of chlorate would be influenced by the dietary forage:concentrate ratio, thus, four ruminally-cannulated steers were fed 20 or 80% concentrate diets in a cross-over design. Ruminal fluid was collected in two periods and dispensed into in vitro tubes containing sodium [36Cl]chlorate sufficient for 100 or 300 ppm final chlorate concentrations. Tubes were incubated for 0, 1, 4, 8, 16, or 24 h; autoclaved control ruminal fluid, fortified with sodium [36Cl]chlorate, was incubated for 24 h. Chlorate remaining in each sample was measured by liquid scintillation counting after [36Cl]chloride was precipitated with silver nitrate. A preliminary study indicated that chlorite, a possible intermediate in the reduction of chlorate, had a half-life of approximately 4.5 min in live ruminal fluid; chlorite was, therefore, not specifically measured in ruminal incubations. Chlorate dose did not affect in vitro dry matter digestion (P greater than or equal to 0.11) whereas in vitro dry matter digestibility was decreased (P less than or equal to 0.05) by 80% forage content. When data were expressed on a concentration basis (ppm), diet had no effect (P greater than or equal to 0.18) on chlorate reduction; however, when chlorate reduction was expressed on a percentage basis, chlorate reduction tended to be greater (P greater than or equal to 0.09) at h 8 and 16 in incubations of the low concentrate diet. Chlorate remaining in autoclaved controls at 24 h was intermediate (P < 0.01) between chlorate remaining in "live" ruminal fluid samples incubated for 0 and 24 h. Attempts to isolate chlorate respiring bacteria from two sources of ruminal fluid were not successful. These data indicate that microbial dependent and(or) chemical dependent reduction of chlorate occurs in bovine ruminal fluid, and that dietary concentrate had a negligible effect on chlorate reduction.