Trichomoniasis is a disease that can sneak into a herd without any obvious signs.
This sexually transmitted disease is caused by protozoa that inhabit the cow’s reproductive tract and the bull’s sheath. It doesn’t affect a bull’s fertility rate, but a bull can spread the disease to many cows during breeding. An infected cow can also infect a bull.
This disease may go undetected until there are too many cows coming up open or late, says Dr. Eduardo R. Cobo, assistant professor of production animal health at the University of Calgary.
“It’s often an early embryo mortality rather than abortion; you usually don’t see the aborted fetus. This is different than most of the other reproductive diseases like brucellosis, leptospirosis, IBR or BVD. When those diseases kill the fetus it might be several months old and you see the abortion,” he says.
The next year, producers might see a drop in pregnancy rates.
Cobo says that scientists in Saskatoon have studied and recognized the disease, but there’s yet to be a survey quantifying its prevalence.
Testing bulls for trich is required in many western U.S. states, but not Canada. Dr. Cheryl Waldner of the University of Saskatchewan says that based on a recent survey, only 21 per cent of Canadian producers test their bulls for trichomoniasis. However, many community grazing associations do require bull testing.
“They also require that cows coming into those pastures have a calf at foot, showing they were able to carry a calf and are probably not infected,” she says.
Community pastures where herds commingle during breeding are among the highest risk situations for this disease to spread between bulls and cows. However, cattle mixing between herds due to fenceline failure can also lead to herd outbreaks.
While trich is not widespread, it can be a very serious problem when it does appear, with very low pregnancy rates, Waldner says.
“One of the reasons producers should pay attention to this disease is that many people are increasing herd size right now. If a rancher is buying cattle from multiple sources, there is more risk,” she says.
Mature bulls present the most risk, but buying open cows, or even heifers that may have already been exposed to a bull, may bring carriers into the herd.
“When a bull is sold, some countries require a certificate showing that a bull is not infected, but this will depend on the country, states or province. And for importing or exporting bulls, some have regulations requiring that you can show that the bull is free of this disease,” says Cobo.
Even if this is not a requirement in your province, it is wise to have every bull tested before purchase. Cobo adds buying virgin or very young bulls also cuts risk. Young bulls have more resistance and a better chance of clearing the infection. Older bulls have more, and deeper, folds of prepuce skin, which is where the protozoa lives. That gives the protozoa a better chance of evading the immune system. Antibiotics treatments are ineffective.
How much the disease might spread also depends on the age of the bull.
“If a bull is young and breeds an infected cow, he may spread the disease for a while but there’s a good chance he will get over the infection.”
Trich is more likely to be chronic in older bulls. Older bulls may carry it into the next year’s breeding season. One strategy is to use young bulls and not keep any bull past four years of age, says Cobo.
As for cows, their immunity may overcome the infection eventually, allowing them to maintain a pregnancy and calve later the next year.
“We don’t know how long this might take, and it may vary from cow to cow. Cows that get over the infection will still be susceptible to becoming infected again,” he explains.
Research from the 1990s showed that even though some cows seem to get over the infection, they still have a low level of trich that is hard to diagnose. Some cows can carry infection from one year to another and infect a bull that breeds them the next year, says Cobo. A scientist at UC-Davis found that some cows still had the infection more than 300 days after they were initially infected.
Cobo recommends checking bulls each year before the breeding season, and only using clean bulls for breeding.
Other recommendations include culling all open cows, buying only virgin bulls, or testing any older bull that has been used on cattle with unknown or suspicious history.
Waldner says some of the wrecks she’s seen occurred in situations when producers had to quickly replace a bull that got hurt in the early part of the breeding season. Sometimes they borrow a bull from a neighbour, or purchase an older bull that is more likely to have been exposed to cows from different sources.
“Infected bulls do not show clinical symptoms. There may not seem to be time to test that bull and have results back before you need to use him, but a sample should be collected for testing in high-risk situations,” she says.
Pulling an infected bull out of the cow herd once test results come in is better than having that bull breed and infect several cows through the rest of the season.
There is no licenced vaccine in Canada for trich, making prevention and early detection even more important.
Since it takes time to get test results back, it’s best to test well ahead of breeding. Also, a sample will be more accurate if the bull has not been breeding cows. If he has been actively breeding, there will be fewer trichomonads, which can lead to a false negative on the test.
Testing at least two months before breeding season also gives a producer enough time to replace a bull if he turns out to be positive for this disease.
When testing a bull, a sample is taken from the smegma in the prepuce surrounding the penis. Semen samples can’t be used for testing.
Trich can be detected with a PCR test or a culture.
“Some clinics use cultures for testing, rather than sending samples to a lab for PCR tests, to reduce costs for individual samples,” says Waldner. “The culture test is also very good, but can have a slight risk of false positives. The PCR test is a little more accurate, and samples from groups of up to five bulls can be pooled to reduce lab costs,” she says.
PCR results also come in faster than culture results.
“Producers should be aware that no tests are sensitive enough to rely on just one negative test. One sample that turns out negative is a good indication the bull is probably not infected, but not 100 per cent guaranteed. When you take a sample from the bull’s smegma in the prepuce, it’s not like a blood sample or semen sample,” says Cobo.
Soil or other contaminants can inhibit a PCR test. Cobo recommends sampling three times at weekly intervals to be sure.
“We have good data showing that the PCR tests commercially available in Western Canada work quite well for testing bulls,” says Waldner. However, she agrees that a single negative test result isn’t a guarantee that the bull is disease-free.
“If there is any reason for suspicion — if you don’t know enough about the situation the bull is coming from, or there was a fence problem and your neighbour’s cattle mixed with yours, or your end-of-season pregnancy rate is lower than usual — you need three tests, to completely rule out this infection,” she says.
The reason for multiple tests is not just because of limitations in the test itself. The risk of false positives with the PCR test is very low, but there is some risk of false negatives.
“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.
Buying virgin bulls or growing your own bulls is the best guarantee for keeping your herd free of trich, as well as not bringing in cows with unknown history.
“It only takes one infected bull to infect many cows, and if it’s an older bull he will be infected for the rest of his life, infecting more cows each year he is used for breeding. You might not suspect a problem, since he will pass a breeding soundness exam, unless you have him tested for trichomoniasis, because this disease does not affect his fertility,” says Cobo.
Vibrio is another venereal disease that should be considered when investigating high open rates in cow-calf herds.
“This disease presents a similar picture in terms of herd history and low pregnancy rates. We can, however, vaccinate cows and bulls to aid in prevention of vibrio,” says Waldner.
While vibrio vaccine is recommended in high-risk situations, no vaccine is perfect. That means producers who are facing reproductive problems may want to ask their veterinarians to test for vibrio as well as trich.
A person may be able to use the same sample for both tests, or may have to take two scrapings, depending on how the samples will be analyzed. Vibrio is harder to culture and diagnose than trich, however, and the tests are not very standardized among the different labs.
“The test for vibrio may not be as accurate as the test for trich, but in high-risk situations where other causes have been ruled out, it can be a useful diagnostic tool,” Waldner says.