|Ross, T - NEW MEXICO STATE UNIV|
|Martinez, C - NEW MEXICO STATE UNIV|
Submitted to: Epidemiology and Infection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 11, 2007
Publication Date: May 17, 2007
Citation: Edrington, T.S., Ross, T.T., Callaway, T.R., Martinez, C.H., Hume, M.E., Genovese, K.J., Poole, T.L., Anderson, R.C., Nisbet, D.J. 2007. Investigation into the seasonal salmonellosis in lactating dairy cattle. Epidemiology and Infection. 136:381-390. Interpretive Summary: The pathogenic bacteria Salmonella is often found in dairy cattle but does not normally make adult cattle sick. However, on some dairy farms, adult cows are made sick by Salmonella, and this always happens at the same time of the year. We sampled sick and healthy dairy cows during an outbreak of salmonellosis in 2003. In 2004, we identified 30 cows, all calving within one month of each other, and sampled them monthly for 9 months. In addition to the fecal samples collected from the cows, we took samples of water, feed, and soil in the pens housing the cattle for Salmonella culture. No differences in the Salmonella isolates collected from sick and healthy cows in 2003 were observed. Prevalence of Salmonella and the type of Salmonella in the feces, feed, water and soil varied considerably from month to month in 2004. The results of this research highlight the difficulty in monitoring Salmonella at the farm level. Not only is the prevalence of Salmonella constantly changing in cattle and the environment, but also the type of Salmonella as well. No major differences were detected when comparing isolates obtained from sick and healthy cattle.
Technical Abstract: Sporadic salmonellosis has been reported in mature lactating dairy cattle in the southwestern United States and is responsible for substantial loss of income for the farmers. This problem is intriguing in that Salmonella can be cultured from the feces of these cattle throughout the year, however it is pathogenic only during the late summer/early fall and only in certain years. In attempting to elucidate possible explanations, we sampled apparently healthy and diarrhoetic cattle during an outbreak on a 2000 head dairy in 2003. The following year, 30 fresh cows from the same farm were identified and monthly faecal samples (February – October) collected. Samples of the total mixed ration (TMR), trough water, and pen soil were also sampled monthly for Salmonella culture. No appreciable differences in serogroup or serotype were observed in comparison of isolates from healthy and sick cattle. No genotypic differences were noted when comparing sick versus healthy isolates using pulsed-field gel electrophoresis, although multiple genotypes within serotype were observed for a number of the isolates examined. Antimicrobial susceptibility patterns were similar among Salmonella isolates cultured from sick and healthy cattle. During year two of the study, Salmonella was routinely cultured from the dairy cattle and the environment each month of the surveillance period, however no outbreak of salmonellosis was observed. Monthly faecal Salmonella prevalence ranged from 19 to 96%, averaging 54% over the 9-month period. The prevalence of Salmonella isolated from total mixed ration (TMR), water and pen soil samples was also highly variable from month to month. Serogroup prevalence varied by month and by sample type with multiple serogroups identified in faeces, TMR, water and soil. Multiple serogroups and serotypes were identified in faecal samples collected from individual cattle. Five isolates randomly selected from one cow’s positive faecal sample were identified as belonging to five different serotypes. The results of this research highlight the complexity of monitoring Salmonella at the farm level. Not only is the prevalence of Salmonella constantly changing in cattle and the environment, but also the predominant serogroup and serotype. Furthermore, no major differences were detected when comparing isolates obtained from sick and diarrhoetic cattle, indicating that determining Salmonella prevalence may be more beneficial than serotype.