Influence of body condition and forage type on prevalence of Escherichia coli O157:H7 and Salmonella in grazing beef cows

Salmonella Carriage in Peripheral Lymph Nodes and Feces of Cattle at Slaughter Is Affected by Cattle Type, Region, and Season

Salmonella is a significant food safety concern in commercial beef production, and some contamination is thought to occur by inclusion of Salmonella-infected peripheral lymph nodes (LN) in ground beef and through fecal contamination. Surveillance in processing plants assists packers in risk management of Salmonella by understanding seasonal trends and risks associated with different cattle types. Approximately 25 fecal samples and 20 LN were collected from animals representing each of five cattle types (cull beef cattle, cull dairy cows, conventional feedlot cattle, all-natural feedlot cattle raised without pharmaceuticals, and grass-finished cattle) and each of five climate regions (mixed-temperatures and dry, mixed-temperatures and humid, hot and humid, hot and dry, cold) during each of three seasons (summer, fall, winter) to better characterize Salmonella inputs into a commercial cattle processing facility. In total, 1,840 fecal samples and 1,550 LN samples were collected. Fecal samples and LN were cultured for Salmonella, and select isolates were serogrouped and screened for antimicrobial resistance. Conventional feedlot cattle had the highest LN Salmonella concentrations (1.17 log10 CFU/g LN) in this data set, while cull dairy cows had the highest fecal Salmonella concentrations (1.96 log10 CFU/g feces). Conventional feedlot cattle and cull dairy cows had the greatest Salmonella prevalence in both LN (32 and 18%, respectively) and feces (37 and 49%, respectively), while all-natural feedlot cattle had the lowest prevalence in the LN (3%) and feces (7%). As expected, Salmonella prevalence and concentration was lowest for all cattle types during winter compared to warmer seasons. When examined by climate region, a greater Salmonella prevalence in both feces and LN was observed in climate region 4 (hot-dry), than the other regions. Only 21 of 50 Salmonella isolates examined for antimicrobial susceptibility were identified as multidrug resistant (MDR); cull dairy cows were responsible for 48% of MDR isolates, cull beef cattle were responsible for 38%, and conventional feedlot, grass-fed, and all-natural feedlot cattle were each responsible for 4.8%. These results indicate that different production schemes, season, and climate region may influence which cattle are most likely to introduce Salmonella to the abattoir, allowing for greater risk awareness during the slaughter process.

A Review of the Use of Organic Amendments and the Risk to Human Health

Historically, organic amendments—organic wastes—have been the main source of plant nutrients, especially N. Their use allows better management of often-finite resources to counter changes in soils that result from essential practices for crop production. Organic amendments provide macro- and micronutrients, including carbon for the restoration of soil physical and chemical properties. Challenges from the use of organic amendments arise from the presence of heavy metals and the inability to control the transformations required to convert the organic forms of N and P into the minerals available to crops, and particularly to minimize the losses of these nutrients in forms that may present a threat to human health. Animal manure and sewage biosolids, the organic amendments in greatest abundance, contain components that can be hazardous to human health, other animals and plants. Pathogens pose an immediate threat. Antibiotics, other pharmaceuticals and naturally produced hormones may pose a threat if they increase the number of zoonotic disease organisms that are resistant to multiple antimicrobial drugs or interfere with reproductive processes. Some approaches aimed at limiting N losses (e.g. covered liquid or slurry storage, rapid incorporation into the soil, timing applications to minimize delay before plant uptake) also tend to favor survival of pathogens. Risks to human health, through the food chain and drinking water, from the pathogens, antibiotics and hormonal substances that may be present in organic amendments can be reduced by treatment before land application, such as in the case of sewage biosolids. Other sources, such as livestock and poultry manures, are largely managed by ensuring that they are applied at the rate, time and place most appropriate to the crops and soils. A more holistic approach to management is required as intensification of agriculture increases.