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Photo: Michael Raine.

Will pooled samples work for vibrio testing?

Sexual health is not just for humans: bulls are known to carry sexually transmitted diseases that can infect cows and heifers during natural breeding.

One infection, which is often found in Canadian cattle herds that use natural breeding, is caused by the bacterium known as Campylobacter fetus subspecies venerealis (vibrio).

"Reproduction is one of the most economically important factors in cow-calf herds. Producers often do not realize they have a reproductive problem in their herd until it is too late," says Dr. Steve Hendrick, a former assistant professor at the Western College of Veterinary Medicine (WCVM).

Bulls infected with vibrio, called "carrier bulls," show no clinical signs of disease, and the infection status of a herd is unclear until the bulls are tested specifically for the disease.

Once cows are infected with vibrio, they will often lose their pregnancy early on and can become temporarily infertile.

"In the fall, producers will have more open cows than they expect or cows pregnant for a shorter duration. Both of these outcomes decrease the number of calves born or pounds of calf weaned the next fall, which decreases the economic success of the herd," explains Hendrick.

"Without proper testing, reasons for poor reproductive performance can go undiagnosed."

Testing breeding bulls for venereal diseases is very important in preventing future herd outbreaks. However, as Dr. Alvaro Garcia Guerra explains, keeping these bacteria alive is very difficult.

"Campylobacter fetus subspecies venerealis has very specific growth conditions. Along with requiring specific nutrients, it must be starved of oxygen and kept warm. Recreating this environment in a field setting can be very difficult," says Garcia Guerra, who completed his Master of Science (MSc) program during the summer of 2013. Investigating vibrio was part of his graduate research.

"Without these requirements, the bacterium can die quickly, which is often the case when samples are transported to diagnostic labs. That's why we have worked to find an alternative test for the detection of vibrio."

In 2011, a former summer research student — Dr. Shirley Chu — designed a real-time PCR reaction that specifically detects Campylobacter fetus subspecies venerealis. While the test is highly specific to vibrio, the cost of running a sample from each bull alone isn't economically feasible to many producers.

That's where I came in. As a summer research student, I ran tests to determine just how sensitive the real-time PCR assay can be: can it detect an infection in a single bull if more than one sample has been pooled together?

My research project's goal was to determine the possibility of testing different sized pools of samples to screen for vibrio in bulls. If this worked, it would provide a useful and cost-effective technique for practitioners to use in commercial operations.

Ideally, veterinarians would collect individual samples from bulls in the field and send them to a diagnostic lab where the samples can be pooled together and tested for vibrio — ensuring that the pool contains the same amount of sample from each bull.

If a pool turns up positive for vibrio, each individual sample can be tested to identify the infected bull. The pool size chosen depends on the number of bulls being tested for vibrio and the likelihood of finding a positive sample in the herd.

With the help of the Agri-Environmental Services Branch's Spring Creek Bull Station near Outlook, Sask., I collected more than 200 samples from yearling bulls as well as bulls known to be infected with vibrio. Last summer, the samples I collected were pooled together in groups of three, five or 10 before being tested with the real-time PCR assay.

Ensuring producers are testing their bulls against vibrio and other reproductive diseases is very important for the cattle industry. Testing for vibrio will provide better disease awareness and vaccination usage, which will aid in reducing the number of infections in cattle herds.

If carrier bulls are removed from a herd before they are turned out for breeding, producers will be able to increase the reproductive efficiency of their herds.

For additional information about WCVM-based vibrio research, read "Real-time PCR undergoes real world testing" on WCVM Today.

Andrea Pellegrino of Calgary, Alta., is a third-year veterinary student who participated in the WCVM's Undergraduate Summer Research and Leadership program in 2013. 
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