Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 2004
Publication Date: June 17, 2004
Citation: Edrington, T.S., Schultz, C.L., Genovese, K.J., Callaway, T.R., Looper, M.L., Bischoff, K.M., McReynolds, J.L., Anderson, R.C., Nisbet, D.J. 2004. Examination of heat stress and stage of lactation (early vs late) on fecal shedding of E. coli O157:H7 and Salmonella in dairy cattle. Foodborne Pathogens and Disease. 1:114-119. Interpretive Summary: Dairy cattle may contain the bacteria E. coli and Salmonella that can make people sick. Many dairies in the United States are located in states with hot climates exposing dairy cows to heat stress. Dairy cows produce more milk early in the lactation cycle and this also causes them stress. Stress in dairy cattle may increase fecal shedding of bacteria. We examined two types of stress in dairy cows: heat stress and stress due to high milk production. Results of these experiments showed that neither of these types of stress affected the shedding of E. coli O157:H7 or Salmonella.
Technical Abstract: Mature, healthy lactating dairy cattle were sampled on two farms in the southwestern United States to examine the effects of heat stress (Experiment I) and stage of lactation (Experiment II) on the fecal shedding of E. coli O157:H7 and Salmonella. To examine the effects of heat stress, fecal samples were collected from 45 cows at 7:00 AM (coolest part of the day) and 5:00 PM (hottest part of the day) in August 2002 on a 250 cow dairy. The study was replicated one month later (n = 170 total samples). A temperature-heat index (THI) was calculated for each sampling time. In Experiment II, stage of lactation was examined by sampling lactating dairy cattle early [< 60 days in milk (DIM)] and late (> 150 DIM) in the lactation cycle in the summer of 2001. The study was replicated the following summer (60 cows/group/replicate; n = 240 total samples). For Experiment I, THI averaged 75 and 82 for the AM and PM samplings, respectively, indicating the cows were beginning to experience heat stress in the morning and by afternoon were in severe heat stress. The shedding of E. coli O157:H7 tended to be higher in the afternoon sampling of the first replicate, however was not different in the second replicate or when both replicates were pooled. Salmonella shedding was not different at any sampling time with nearly 100% of the cows positive. Stage of lactation had no effect on the number of cows shedding E. coli O157:H7. Salmonella shedding tended to be higher in early lactation cows in the first replicate, while in the second replicate more late lactation cows were shedding Salmonella, however there were no differences due to stage of lactation when replicates were pooled. While further research is needed, results of this research highlight the variability in pathogen shedding in healthy dairy cattle and indicate that environmental factors and/or production demands may influence shedding patterns of E. coli O157:H7 and Salmonella.