March 24, 2022
Trichomoniasis is a sexually transmitted disease that can sneak into a cow herd without any signs. The first thing a stockman might see are cows returning to heat when they should be pregnant. This disease is caused by protozoa living in the reproductive tract of cows and the sheath of bulls. It occurs most often when ranchers use untested bulls, purchase open cows with unknown background, or when cattle herds commingle.
“Trich” has been a problem for many years in western states, and most of them have taken steps to control it with import regulations and testing. Idaho was the first state to require mandatory annual testing of bulls, in 1989. In 2000 the Wyoming Livestock Board established the first rules for trich in Wyoming.
Dr. Jim Logan, who retired as Wyoming’s State Veterinarian in 2021, says it seems to be impossible to eradicate.
“In spite of the fact that most western states have rules and requirements for testing, trich continues to show up. Most states require testing of bulls prior to sale, and if infection is found in a herd there are quarantines—always the bulls, but in some cases the cows are also quarantined. Yet this disease continues to raise its ugly head,” said Logan.
Some stockmen still don’t test their bulls, and some purchase cattle with unknown history. This puts neighbors’ herds at risk if cattle mingle on public rangeland or a bull goes through a fence to breed a neighbor’s cow—or an infected cow gets into the neighbor’s place and is bred by the neighbor’s bull, which becomes infected.
“A small percentage of females can act as carriers without showing signs of the disease. Open females and cows that calve late in a herd should be culled,” he said.
Dr. Eduardo Cobo, University of Calgary, says trich is often under-diagnosed. “Producers may also think vaccination will prevent the problem, but vaccination is not very efficient for protecting cows,” he said.
“My former supervisor at University of California, Davis, Dr. BonDurant, found that up to 15% of beef herds in California had at least one bull infected with trich. The trichomonads can be detected with a PCR test or a culture. When I moved to Canada in 2011 and started talking with stockmen there, many didn’t think trichomoniasis was a concern, but there wasn’t much testing being done,” said Cobo.
Certificate sometimes required
“When a bull is sold, some countries require a certificate showing that a bull is not infected, but this depends on the country, state or province. And for importing or exporting bulls, some have regulations requiring that you can show that the bull is free of this disease,” said Cobo. Even if this is not a requirement where you live, it is wise to have every bull tested before you buy him.
Cobo recommends buying virgin bulls or very young bulls. “Young bulls have more resistance against the protozoa and more chance to clear themselves of infection. This parasite lives in folds of the prepuce skin and older bulls have more (and deeper) folds where these protozoa can hide (thriving in an environment without oxygen) and be hidden from the immune system.” Treating bulls with antibiotics to try to clear the infection doesn’t work because most drugs are not effective against protozoa, or don’t reach them; it’s difficult to get drugs into areas where protozoa are hiding. Bull fertility is not affected by this disease, but the bull is spreading it to cows.
This disease kills the embryo or fetus, usually in the first 3 months of gestation. The cow is bred and becomes pregnant, but the pregnancy doesn’t last long. It generally happens so early that you don’t see an aborted fetus. Usually the embryo is so small that it is simply absorbed by the uterus. You just see the cow return to heat and think she didn’t settle from the first breeding.
“The next year you don’t have the pregnancy rate you’d expect. The bull is the main factor because he can infect many cows, spreading it from an infected cow to all the others he breeds. This disease is more common in beef cattle than dairy because many dairy cows are bred by AI and not a bull,” said Cobo.
How much the disease might spread depends on the age of the bull. A virgin bull is safest to use because he won’t be infected so easily. If you use a virgin bull on heifers (that have never been infected) there will be practically no chance for this disease to occur. “If a bull is very young and breeds an infected cow, he may spread the disease for a while but there’s a good chance he’ll get over the infection himself. Trichomoniasis is more chronic in older bulls; they may carry it into next year’s breeding season. One strategy is to use young bulls and not keep a bull past 4 years of age,” he said.
Though bulls are the main carriers, cows sometimes act as carriers. A scientist at UC-Davis was infecting cows and checking them every week, and found that some cows still had the infection more than 300 days later.
Bulls should be checked every year before breeding season, and only “clean” bulls used for breeding. To test the bull, a sample is taken from secretions in the prepuce surrounding the penis, where the parasite lives. “These protozoa don’t live in the semen or testicles; they live in secretions in the skin around the penis,” Cobo said. Semen samples won’t detecting this disease.
“Depending on your state or province, you may be required to have 2 or 3 tests showing the bull is negative. Producers need to be aware that the tests are not sensitive enough to rely on just one negative result; it’s not 100% guarantee. The PCR test might be inhibited by some other contaminant. You really need to take 2 or 3 samples at weekly intervals to know if he bull is actually negative.”
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. “You might not suspect a problem (since he will pass a breeding soundness exam) unless you have him tested for trich, because this disease does not affect his fertility. Yet he’ll keep spreading the disease each year that he breeds cows,” said Cobo.
Since it takes time to get test results back, it is important to do the tests well ahead of breeding. Also, the sample will be more accurate if the bull has not yet been breeding cows. If he has been actively breeding, the level of trichomonads will be lower, and you might get a false negative on the test.
Logan’s advice to producers is to follow their state’s recommendations and rules. “Annual testing of bulls is important, along with sending open cows to slaughter—so they won’t end up in someone else’s herd,” he said. “Some producers, especially those new to raising cattle, may end up putting themselves and their neighbors at risk.”
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