Brown-Brandl Tami M, Berry Elaine D, Wells James E, Arthur Terrance M, Nienaber John A
U.S. Meat Animal Research Center, Agricultural Research Service, U.S. Department of Agriculture, Clay Center, Nebraska 68933, USA.
Foodborne Pathog Dis. 2009 Sep;6(7):855-64. doi: 10.1089/fpd.2008.0222.
The reduction of foodborne pathogens in cattle destined for human consumption will require knowledge of the factors that impact the carriage and shedding of these organisms. The objective of this work was to investigate the effects of heat and handling stress levels on the fecal shedding of Escherichia coli O157:H7 and generic E. coli by feedlot cattle. In year 1, 128 feedlot heifers were evaluated for heat tolerance five times per week during the 84-day finishing period from May through August. Heat stress measurements included respiration rate, panting score, and visual assessments. In year 2, panting scores were taken for a group of 256 finishing feedlot heifers on days in July and August for which the temperature humidity index (THI) was predicted to be in the "emergency" category (THI > or = 84). For both years, animals were weighed and temperament scored to assess handling stress on a 28-day schedule. At the same time, rectal fecal samples were collected from each animal individually. The presence and concentrations of E. coli O157:H7 and concentrations of generic E. coli in feces were determined. There were no clear trends between the heat stress levels or temperament scores (as an indicator of response to handling) with either fecal generic E. coli concentrations or E. coli O157:H7 concentrations or prevalence in feces, indicating that neither heat nor handling stress contributes to the food safety risk associated with E. coli O157:H7-positive cattle.
减少供人类食用牛的食源性病原体需要了解影响这些生物体携带和排泄的因素。这项工作的目的是研究热应激和处理应激水平对饲养场牛粪便中大肠杆菌O157:H7和普通大肠杆菌排泄的影响。在第1年，从5月到8月的84天育肥期内，每周对128头饲养场小母牛进行5次耐热性评估。热应激测量包括呼吸频率、喘气评分和视觉评估。在第2年，在7月和8月温度湿度指数（THI）预计处于“紧急”类别（THI≥84）的日子里，对一组256头育肥饲养场小母牛进行喘气评分。在这两年中，按照28天的时间表对动物进行称重和性情评分，以评估处理应激。同时，从每只动物个体采集直肠粪便样本。测定粪便中大肠杆菌O157:H7的存在和浓度以及普通大肠杆菌的浓度。热应激水平或性情评分（作为对处理反应的指标）与粪便中普通大肠杆菌浓度、大肠杆菌O157:H7浓度或粪便中的流行率之间没有明显趋势，这表明热应激和处理应激均不会增加与O157:H7阳性牛相关的食品安全风险。
