Background 

Every year more than 76 million Americans become ill from the consumption of food contaminated with pathogenic bacteria. The bovine gastrointestinal tract is a well recognized reservoir for bacterial pathogens like Escherichia coli O157:H7, Salmonella and Campylobacter. In the United States these bacterial pathogens are responsible for more than 3.5 million human infections annually at an estimated annual cost of more than $3.5 billion a year. As many as 66% of the cull dairy cow markets have detectable amounts of Salmonella shedding and these cull cow markets contribute substantially to the ground beef available for consumption. Thus, pre-harvest intervention strategies that reduce the shedding of food-borne pathogens in cull dairy cattle are essential to reducing the amount of pathogenic bacteria entering slaughter facilities and potentially contributing to contamination of food products and human infections. Sodium chlorate supplementation has been investigated as a pre-harvest food safety strategy to reduce Salmonella and E. coli O157:H7 in vitro and in food producing animals. Research has also shown that the addition of short chained nitro compounds like nitroethane can enhance the ability of sodium chlorate to reduce if not kill Salmonella and E. coli as much as ten-fold in vitro and in vivo. Based on the research done to date, sodium chlorate technology shows great promise for reducing Salmonella and E. coli O157:H7 pre-harvest. 

The objective of the current research was to determine if feeding sodium chlorate, with and without nitroethane, is effective in reducing populations of Salmonella, E. coli O157:H7 and generic E. coli in cull dairy cattle on a commercial dairy prior to slaughter.

Methodology 

All cattle were obtained from a conventional commercial dairy in the southwestern United States. Dairy cows that were sent to the hospital pens per the dairy’s standard operating procedures were prescreened for Salmonella. Five days post-sampling, animals confirmed as Salmonella positive were enrolled in this study. Twelve lactating Holstein dairy cows (average BW 545 kg) testing positive for Salmonella were purchased from the dairy and six animals were randomly assigned to each treatment (chlorate or chlorate + nitroethane). All experimental animals remained on the dairy and were housed in a pen separate from the rest of the dairy herd, otherwise all feeding and management schemes were as normal for the dairy. 

Salmonella positive animals received 42 mg/kg BW/d sodium chlorate or 21 mg sodium chlorate/kg BW + 160 mg nitroethane kg/BW/d. Treatments were administered 4 times at 12 h intervals via stomach tube. Fecal grab samples were collected just prior to first dosing and subsequently every 12 h for the next 48 h post initial dosing. Following the last fecal collection animals were humanely euthanized. Luminal contents and tissues from the rumen, small intestine, cecum, spiral colon and rectum were aseptically collected upon necropsy and analyzed for quantitative and qualitative bacterial culture of Salmonella, E. coli O157:H7, generic e. coli and fecal coliforms.

Findings 

The scope of this experiment was to evaluate the effects of sodium chlorate with and without nitroethane on fecal shedding of Salmonella, E. coli O157:H7 and generic E. coli in cull dairy cows. The experiment was performed on the farm to ensure that daily farm practices and feeding regimes were employed in an effort to accurately simulate real world application of the sodium chlorate and sodium chlorate + nitroethane products. Two animals in the chlorate treatment group were shedding Salmonella at high concentrations at the time of pre-screening. Figure 1 demonstrates the ability of the sodium chlorate product to effectively reduce (5 logs) Salmonella in animals colonized with high concentrations. The remaining animals were positive for Salmonella following enrichment at pre-screening. Forty-eight hours post initial treatment with sodium chlorate all animals were negative for Salmonella via spiral plating and only fifty percent of the animals had any detectable amount of Salmonella from enriched samples. Sodium chlorate + nitroethane treatment resulted in all animals testing negative for Salmonella via spiral plating and only thirty three percent of the animals had any detectable amount of Salmonella from enriched samples. Luminal contents from the sites sampled at necropsy yielded no detectable Salmonella via direct plating for all animals regardless of treatment. Animals were negative for E. coli O157:H7 via direct plating and enrichments. Generic E. coli and fecal coliforms were high across all animals tested for fecal samples taken over time post dosing suggesting that there was little effect of the sodium chlorate or sodium chlorate + nitroethane treatments on generic E. coli or fecal coliforms. 

The results of the research presented herein support the use of chlorate as a pre-harvest intervention for use in cull dairy cattle. Administration of sodium chlorate immediately following the decision to cull an animal should allow adequate time for the chlorate to exert its killing effect on Salmonella prior to the animal entering the slaughter facility. While the sodium chlorate did not kill 100% of the cultured Salmonella, it did significantly reduce populations in the high shedders to levels that are effectively controlled by modern processing intervention strategies. Subsequent research should examine the effectiveness of on-farm sodium chlorate administration by following cull animals through the slaughter process. 

Implications 

Results of this research demonstrate the ability of sodium chlorate to effectively reduce Salmonella populations in cull dairy cattle. On-farm administration of this compound upon identification of an animal for culling should effectively reduce the Salmonella burden entering the slaughter facilities, thereby providing a safer beef product to the consumer.