A new vaccine and a beneficial bacterial feed additive each significantly reduced E. coli O157:H7 in feedlot cattle, and using both may offer added protection, University of Nebraska research shows.
For the past two summers, NU agricultural scientists tested the effectiveness of both E. coli control methods under typical feedlot conditions in studies of more than 1,100 cattle in the university's feedlots.
Results of these extensive trials look promising, said Terry Klopfenstein, an animal scientist on the NU Institute of Agriculture and Natural Resources' research team.
"It looks like there are things in the works that can make a significant difference in controlling this organism," he said. That is good news for beef producers who are eager for science-based tools to help them reduce prevalence of this dangerous bacteria on farms and in feedlots. E. coli O157:H7 is the culprit in numerous foodborne illness outbreaks and ground beef recalls.
For these studies both years, steers received either: a developmental vaccine, a commercially available Lactobacillus acidophilus feed additive as a direct-fed microbial or no treatment. During 2002, some steers received both the vaccine and feed additive.
The vaccine proved most effective at reducing the proportion of cattle shedding E. coli in their manure. Vaccination reduced E. coli prevalence an average of 59 percent in each year compared with unvaccinated steers, said NU Veterinary Scientist David Smith.
Feeding Lactobacillus acidophilus, a specially selected strain of a bacteria commonly used in yogurt, reduced prevalence an average 35 percent compared with untreated steers in a two-year study.
While E. coli prevalence varied greatly across time and pen to pen, it consistently was lower in cattle that received the vaccine, the direct-fed microbial or a combination of the two, compared to untreated pens.
In 2003, E. coli prevalence averaged less than 11 percent for vaccinated steers compared with 29 percent among unvaccinated steers, Smith said. In 2003, prevalence among cattle fed Lactobacillus averaged under 21 percent compared with 28 percent in untreated steers.
Knowing when and where E. coli is being shed in manure is key to accurately evaluating any control's effectiveness in real-world conditions, Smith explained. Nebraska scientists sampled manure from individual animals at intervals throughout the feeding period to track fluxes in prevalence.
At market weight 84 days after vaccination in 2003, 19 percent of vaccinated cattle and about 34 percent of those fed Lactobacillus were shedding O157:H7 compared with nearly 41 percent of the untreated cattle.
In 2002, the NU team also evaluated the effectiveness of the vaccine/Lactobacillus combination and found it boosted overall control somewhat. At marketing, about 9 percent of steers that received the combination were shedding E. coli compared with about 17 percent of vaccine-only steers, about 23 percent of the Lactobacillus-only group and 26 percent of untreated steers.
"When we used them in combination, we observed an additive effect," Smith said. "Since they work differently, you could expect to get benefit from using either or both."
The Lactobacillus gets ingested with rations and travels to the cattle's digestive system where it's thought to kill or impair growth of E. coli. The vaccine stimulates cattle's immunity against proteins that allow E. coli to attach to cattle's intestinal tracts. If it can't attach, the organism can't stick around to multiply, explained Veterinary Scientist Rod Moxley. That ultimately means cattle are shedding less E. coli so less of the organism winds up in the environment through manure.
Moxley's analysis of blood tests also showed the vaccine induced significant immune response against specific E. coli proteins in the cattle.
Because O157:H7 is common in feedlots and can be reintroduced from other sources, complete eradication isn't likely. But controls that help reduce the organism at key times and perhaps cumulatively over time will have a significant effect, Moxley said.
Alan Janzen, a beef producer who owns Circle Five Feedyards at Henderson, Neb., agreed. Janzen has been involved in numerous national food safety efforts, including a stint as chair of the Beef Industry Food Safety Council's policy committee.
Meat packers have asked beef producers to reduce E. coli levels by half in cattle delivered for slaughter, he said. Such a reduction combined with improved food safety controls at processing plants should be a one-two punch to control E. coli and protect consumers.
"I'm very excited and looking forward to the point in the very near future where we've gotten on top of this organism," Janzen said.
Janzen already uses the direct-fed microbial product in his operation. He said he thinks industry will more readily accept the vaccine if it is incorporated into a combination injection, instead of a stand-alone vaccine. Producers will have to pay the additional vaccine cost with no direct benefit.
Like most producers, Janzen does all he can to hold down costs, but said he expects to use an E. coli vaccine when it's available. He's willing to absorb some added expense to improve his on-farm food safety.
"This E. coli has cost our industry $3 billion so wouldn't it be worth something to get us past it?" he asked.
Janzen is especially enthused about the potential for reducing the organism in his feedlot environment over time.
"I'm excited about that environmental effect," he said. "If I have interventions in my yard, clean up my environment and vaccinate cattle coming in, over time, I will eliminate the organism from the systems in my yard."
The vaccine used in the NU trials is being developed by an alliance of Canadian groups including the University of British Columbia, the University of Saskatchewan's Vaccine and Infectious Disease Organization, the Alberta Research Council and Bioniche Life Sciences Inc., a biopharmaceutical company responsible for worldwide commercialization. NU researchers have collaborated with colleagues Andrew Potter of the University of Saskatchewan, Brett Finlay of the University of British Columbia, who developed the experimental vaccine, and with Bioniche scientists to test the vaccine's effectiveness.
Bioniche expects its E. coli vaccine could be available in the United States in 2004, pending completion of current studies and receipt of regulatory approvals.
The Lactobacillus feed additive is produced by Nutrition Physiology Corp., an Indiana-based feed supplement company. It's commercially available and already used in some feedlots.
NU scientists recently received another U.S. Department of Agriculture grant to expand vaccine and direct-fed microbial efficacy trials to the region's commercial feedlots next summer. They conduct their trials during the summer months because that's when E. coli typically is most prevalent in feedlots.
"Our goal is to help the cattle industry in Nebraska find ways to reduce this organism and ultimately protect human health," Klopfenstein said.
These feedlot trials are part of intensive interdisciplinary research by NU scientists to understand E. coli, how it behaves in feedlots and how to reduce it in cattle before slaughter. Collaboration with Nebraska's beef industry and feedlot operations helped the team develop extensive understanding of how E. coli behaves under real-world conditions.
The Nebraska Beef Council, the U.S. Department of Agriculture, Nutrition Physiology and Bioniche Life Sciences helped fund this IANR Agricultural Research Division research.
Materials provided by University Of Nebraska-Lincoln. Note: Content may be edited for style and length.
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