By: Russ Daly, SDSU Extension Veterinarian
As area beef herds become involved in making decisions about bulls for next breeding season, herd health and reproductive disease should be considered in the context of what age and type of bulls are being purchased.
Perhaps the one reproductive disease for which the bull plays a critical role in transmission is that of trichomoniasis, or "trich". This disease has been around for generations and for many years was thought to be something only states west of the Rocky Mountains had to concern themselves with.
That changed for South Dakota cattle producers back in 2004, when over 40 herds were detected with the disease and were faced with the task of cleaning it up. A cooperative effort between the South Dakota Animal Industry Board and cattle producer organizations resulted in the implementation of regulations that not only tackled importation of the disease, but also its spread within the state. These regulations involve testing of all non-virgin bulls moving into the state or between herds, as well as the prohibition of open cows being sold back into breeding herds. While South Dakota has enjoyed several years of very few new infections, other surrounding states have not been as fortunate, and trich is very much at the top of their producers’ minds, as it was for South Dakotans 10 years ago.
Trich is caused by a protozoal organism that lives indefinitely in the sheath of an infected bull. Once it’s transmitted to a female through the act of breeding, it causes an inflammation in the reproductive tract that results in the loss of the pregnancy. While infected cows can clear themselves of the infection, bulls remain positive for life. Therefore, detection strategies for this disease come down to testing the bull.
Testing for trich is among the most-discussed aspects of the disease right now. We have come a long way over the past 10 years in the methods used for detecting the organism. What has not changed is the location and means of collecting a sample: the preferred sample is a scraping from inside the bull’s sheath. This is where the protozoa live, protected by the microscopic peaks and valleys in the skin inside the sheath.
But where we used to need to culture (grow) the organism so we can visually detect it in a plastic pouch filled with nutrients, we now can take a sample and submit it for polymerase chain reaction (PCR) testing. This is a very sensitive diagnostic technique that can detect just a few organisms, as well as those that are no longer living. The culture method was fraught with enough short-comings (survival of the organism in freezing temperatures on the way to the lab was one of them) that regulations required taking three samples at weekly intervals from the bull in order to ensure that an infection was not missed.
While states and laboratories have embraced PCR testing for trich, there remains controversy about testing methods. The issue is that every lab has its own special method for testing. Some require that samples be submitted in culture pouches; some (like SDSU) will say that submitting them in a tube of saline is good enough. Some labs and states do not want veterinarians to pool (combine) samples; others are fine with it for 2 or 3 bulls. And then there are the slightly different techniques employed in the PCR testing itself.
It’s these differences between labs and state testing regulations that have some people concerned, to the point where a special summit meeting is scheduled for April 2014 to come up with standardized procedures. In theory, the possibility exists that one lab might do a better job than another when it comes to detecting trich. In reality, this is yet to be shown. However, it is possible that such efforts may result in more standard, across-the-board testing requirements coming down from state agencies.
Regardless, improvements in test sensitivity and in awareness of trichomoniasis have significantly reduced the risk of its introduction into our cattle herds overall. However, it’s a long way from being eradicated – and will remain a consideration for cattlemen for a long time to come.