Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2009
Publication Date: 5/2/2009
Citation: Edrington, T.S., Carter, B.H., Friend, T.H., Hagevoort, R., Poole, T.L., Callaway, T.R., Anderson, R.C., Nisbet, D.J. 2009. Influence of sprinklers, used to alleviate heat stress, on faecal shedding of E. coli O157:H7 and Salmonella and antimicrobial susceptibility of Salmonella and Enterococcus in lactating dairy cattle. Letters in Applied Microbiology. 48:738-743.
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. Farmers use sprinklers to reduce the effects of heat stress in milking cows. Stress in dairy cattle may increase fecal shedding of bacteria. We examined the use of two types of sprinkler application (feedbunk and holding pen) to reduce heat stress in milking cows, and examined fecal shedding of E. coli 0157:H7, Salmonella. Results of these experiments showed that the use of feedbunk sprinklers did not have any affect on pathogenic bacteria, while cows exposed to sprinklers in the holding pen had a lower prevalence of Salmonella. Identification of management techniques used by dairy farmers to reduce stress could reduce on-farm pathogen levels.
Technical Abstract: To determine the effect of sprinklers on fecal shedding of E. coli 0157:H7 and Salmonella in lactating dairy cattle and examine isolates for antimicrobial susceptibility, sprinklers were applied to lactating dairy cattle on two commercial farms at either the feedbunk or in the holding pen prior to milking. One pen of cattle on each farm received the sprinkler treatment, and one pen of cows (at the same stage of lactation) served as untreated controls. Fecal samples (fresh, undisturbed pats from the pen floor) were collected approximately one and four weeks following initiation of sprinkler treatments for culture of E. coli 0157:H7, Salmonella, and Enterococcus. Antimicrobial susceptibility was determined on select isolates using the broth microdilution and the NARMs panel for gram-negative isolates. No treatment differences were observed for E. coli 0157:H7 on either farm with very few samples culture positive. Salmonella was numerically higher (P = 0.11) in the control treatment on day 7, whereas on day 28, the bunk sprinkler treatment had a significantly greater number of cows Salmonella positive. When combined across days, no differences were observed in Salmonella shedding due to feedbunk sprinkler application. The prevalence of Salmonella in cattle exposed to sprinklers prior to milking was decreased (P = 0.0001) on day 5, and when combined across days, but not different on d 26 when compared to control animals. Results of the antimicrobial susceptibility screening found very few isolates were multi-drug resistant, and most resistance observed were to antimicrobials commonly utilized in veterinary medicine. All of the Enterococcus isolates were susceptible to vancomycin. This study demonstrated a significant decrease in fecal prevalence of Salmonella in lactating cattle following exposure to sprinklers administered prior to milking. Identification and implementation of on-farm strategies for reducing pathogenic bacteria at the farm level can have significant food safety, herd health, and environmental implications.