Contamination of beef carcasses with pathogens such as E. coli, and Listeria during slaughter and processing have led to the annual recall of over 1.8 million pounds of beef during the last decade; this average excludes a recall of 22 million pounds of beef in 2002. Food-animal products containing undetected pathogens continue to contribute to an un-quantified number of foodborne illnesses. In beef cattle, it has been established that hides are a major source of carcass contamination and that hide washing intervention steps effectively reduce subsequent pathogen loads on carcasses. Although post-harvest sanitation techniques are becoming increasingly efficient, they are in use because no practical methods exist for eliminating pathogens from live animals prior to slaughter. Recently, a new pre-harvest technology that greatly reduces, or eliminates, the numbers of Gram-negative pathogens inhabiting gastrointestinal tracts of cattle has been developed. The technology is based on the feeding of a sodium chlorate containing product (ECP) 24 to 72 h prior to an animal’s slaughter. During the chlorate exposure period, bacterial species containing intracellular respiratory nitrate reductase are thought to metabolize chlorate (ClO3 -) to the bacterial toxin chlorite (ClO2 -). Chlorate toxicity is specific to nitrate-reductase containing bacteria that have the ability to intracellularly convert chlorate to chlorite, but which lack chlorite dismutase enzymes capable of rapidly detoxifying chlorite to chloride. Use of chlorate does not adversely affect the commensal microflora of gastrointestinal tracts. Unlike many antibiotics, development of chlorate resistance seems to occur only in pure bacterial cultures and not in mixed bacterial cultures.
Our laboratory has previously determined that sodium [36Cl] chlorate administered to ruminating cattle is transformed only to the chloride (Cl-) ion, although residues of parent chlorate ion were present in edible tissues. Because chloride is a nutrient essential for life in mammalian and avian species, the presence of chloride residues in animal tissues does not represent a food safety risk. Chlorite (ClO2 -) ions, which could be of food safety concern, were absent from edible tissues and urine of chlorate-treated cattle. Chlorate residues present in skeletal muscle and kidney were greater than estimated safe tissue concentrations of chlorate. But because cattle were exposed to chlorate for three consecutive days, with a dose representing 150% of the target dose, and because the cattle were slaughtered with an 8-hour withdrawal period, high chlorate residues in skeletal muscle and kidney were not believed to represent insurmountable obstacles for further development of sodium chlorate as a feed additive. The purpose of this study was to determine the effect of sodium chlorate dose on chlorate residues in edible tissues of cattle slaughtered with a 24-hour withdrawal period, and to determine if the magnitude of chlorate residues in skeletal muscle and kidney would be prohibitive for further development of chlorate as a possible pre-harvest pathogen intervention strategy.
The objectives of the study were to identify a dose of sodium chlorate that results in acceptable chlorate residues in edible tissues of cattle.
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