Importance of Testing Bulls for Trichomoniasis Between Breeding Seasons
By : Heather Smith Thomas
Trichomoniasis (“trich”) is a reproductive disease that results in early pregnancy loss and open cows. The first thing a producer might notice are cows returning to heat when they should be pregnant. This sexually-transmitted disease is caused by protozoa that live in the reproductive tract of cows and sheath of bulls and occurs most often when stockmen use untested bulls, purchase open cows with unknown background, or when cattle herds co-mingle during breeding season.
Dr. Bart Lardner, Research Scientist, University of Saskatchewan, recommends testing bulls before or after breeding season, especially if cows are bred in community pastures. In a closed herd, this disease may not be an issue–unless a neighbor brings in new cattle and an infected cow or bull comes through the fence.
“Often producers don’t realize they have trich in their herd until they have a high percentage of open cows in the fall, or some cows cycle all summer long. Sometimes a producer is unaware of the risk when bringing in a new bull,” says Larder. There is also risk when buying open cows. Unless it’s a virgin heifer, any open female could be carrying this disease. Mature bulls are the biggest risk, but buying open cows, or heifers that may have already been exposed to a bull, could bring carriers into the herd.
This disease has been a problem for many years in western states, and most states try to control it with import regulations and testing. Idaho was the first state to require mandatory annual testing of bulls, beginning in 1989.
Dr. Jim Logan, Wyoming State Veterinarian, says, “We can’t seem to eradicate this disease. In spite of the fact that most western states now have rules and requirements for testing, trich continues to show up. Part of the problem is that we don’t have a good test for females. A small percentage of females can act as carriers. Open females and cows that calve should be culled—
and sold only for slaughter so they don’t end up in someone else’s herd,” Logan says.
For many years the only way to check for trich was to take a sample from the bull’s sheath and culture it. This gives a 90% chance of finding the organism if the bull is infected. Standard practice is three cultures. If they all come up negative there is only one chance in 1000 that the bull is infected. Today, many veterinarians and producers choose a PCR test, which is more accurate and faster. PCR tests are becoming more affordable, and speed things up, especially if a producer wants to turn bulls out soon and doesn’t want to wait so long for test results.
Cheryl Waldner, DVM PhD, University of Saskatchewan, says producers wonder how many times they should test each bull, since a few infected bulls won’t show up positive on just one test. “One negative test may be adequate in low risk situations. For example if the bull has been in your herd several years, has always had good pregnancy rates, and has not been exposed to any high risk cattle, one negative test may be enough.
“If you are not sure, for instance if your bull has been exposed to other cattle besides your own herd, or it’s a borrowed or leased bull, you’ll need more tests. If there is any reason for suspicion—if you don’t know enough about the bull’s history, or there was a fence problem and other cattle mixed with yours, or your end-of-season pregnancy rate is lower than usual— you need three tests, to rule out this infection,” she says.
The risk of false positives with the PCR test is very low, but there is some risk of false negative results. “Another problem is inconsistency in what we get from the bull, and the number of organisms being shed when we take samples. These numbers can fluctuate over time, and between samples,” says Waldner. You have a better chance to identify the infection if you take repeated samples, at least a week apart.