Recently, I was reading a couple of research reports on a new E. coli O157:H7 cattle vaccine. The vaccine, which is meant to reduce the incidence of the microbe in feedlot cattle, has not yet been approved for use in the United States and has “investigational” status in Canada.
What caught my eye in these reports was the mention of the use of growth implants. These are pellets which are placed under the skin of the ear and slowly release growth hormones into the animal’s bloodstream. The hormones help the cattle “bulk up” more rapidly - just like athletes on anabolic steroids.
Growth promoting implants have been used by beef producers for more than 30 years. There are hundreds of articles in the scientific and technical literature touting the economic benefits of various growth-promoting hormones. I decided to check whether anyone had thought to investigate whether the use of these hormones might have an impact on the susceptibility of cattle to become colonized with E. coli O157:H7.
As far as I can tell, only one study has addressed this issue. A group of Canadian researchers systematically tested the effects of a growth promoting implant and the use of antibiotic feeding supplements on the presence or absence of E. coli O157 in cattle feces. In this study, some of the cattle (the control group) received neither hormones nor antibiotics; the others received a hormone implant, an antibiotic supplement, or both. At various times during the course of the 165-day experiment, feces from all of the cattle were tested for E. coli O157.
At no time during the entire study was E. coli O157 found in the feces of the “control” group - the cattle that received no hormones and no antibiotics. In contrast, more than half (54%) of the treated animals were positive for E. coli O157 at least once. The authors of the report (published in the Journal of Food Protection in November 2006) concluded that “...the high prevalence of E. coli O157 we observed may have been caused by the administration of growth-promoting agents...”
The authors went on to note that the differences between the treated and untreated cattle were not statistically significant. This was likely due, at least in part, to the small size of their experiment (only 80 animals in total). They went on to suggest that a larger study would allow more conclusive results to emerge. While we’re waiting, anyone for a hamburger?