Trichomoniasis testing might be in order for bulls if your calf crop is smaller than anticipated
Trichomoniasis is a disease that can sneak into a herd without much warning. The first thing a producer might notice are cows returning to heat when they should be pregnant, or a high percentage of open cows after the breeding season.
This sexually transmitted disease is caused by tiny protozoa that inhabit 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 (that might be carrying this disease), or when cattle herds co-mingle.
A cow infected at breeding does not get sick, but the infection in her reproductive tract kills the developing embryo or fetus within the first weeks or months of gestation. The cow returns to heat and might get bred again, but generally does not settle until she clears the infection. Her reproductive tract usually recovers after two or three more heat cycles. By then the bulls may have been taken out of the herd. Thus this disease results in open or late-bred cows, reducing next year’s calf crop.
A few cows may carry the disease into the next year if they are infected late in the season, but bulls are the main source of spread. Young bulls may clear an infection after a period of sexual rest (such as over the winter if they are not with any cows), but older bulls often remain infected for the rest of their lives. These protozoa live in the tiny pockets and creases in the inner surface of the sheath, and older bulls have more folds in the sheath where protozoa can survive for long periods in this airless environment.
Trich has been a problem for many years in western states, and most of those states have taken steps to try to control it, with import regulations and testing. Idaho was the first state to initiate mandatory annual testing of bulls, in 1989. Dr. Debra Lawrence, Idaho State Veterinary Medical Officer, said that for a while 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 parasite if the bull is infected. A repeat test a week later leaves a 10% to 20% chance of having a false negative. Standard practice is to do three cultures, a week apart. If they all come up negative there is only one chance in 1,000 that the bull is infected. Today, however, many breeders choose to use a PCR test, which is more accurate and faster.
“It is becoming more affordable, and we can also do it here in our lab, whereas in the past those samples had to be sent to UC-Davis,” Lawrence said. Even though a single PCR test is very accurate, some state regulations still require that any bull coming into the state from an unknown background must have three tests a week apart, whether they are PCR or a culture.
Testing bulls annually for trich (before the next breeding season) is required in many western U.S. states, but not in Canada, since this disease is less common.
Dr. Cheryl Waldner, DVM PhD and a professor at the University of Saskatchewan, said that based on a recent survey, only 21% of Canadian producers test their bulls for trichomoniasis. “Although testing is not officially required on cattle that are moving between operations, there are many communal grazing associations that do require bulls to be tested, and require that cows coming into those pastures have a calf at foot (showing that they were able to carry a calf and are probably not infected),” she said. Community pastures where herds are comingled during breeding are among the highest risk situations for this disease to be passed from infected bulls to cows, and then from infected cows to other bulls. However, cattle mixing between herds due to fence-line breaches can also lead to herd outbreaks.
Dr. Jim Logan, Wyoming State Veterinarian said it seems impossible to eradicate this disease. “In spite of the fact that most western states have rules and requirements for testing, trich continues to show up in these states and continues to be a problem. 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. In spite of this, the disease continues to raise its ugly head,” Logan said.
“People can make good rules, based on science, that look good on paper. But until the entire industry steps up and complies with the rules, it will be very difficult to get rid of this disease,” he said. In spite of rules, some stockmen don’t test their bulls. Some ranchers purchase cattle with unknown history. This puts their neighbors’ herds at risk if cattle mingle on public rangeland or a bull goes through a fence to breed the neighbor’s cow — or an infected cow gets into the neighbor’s place and is bred by the neighbor’s bull, which then becomes infected.
Trich can be a very serious problem when it does appear. If a rancher buys cattle from multiple sources, there is more risk. Mature bulls coming from another herd are the biggest risk, but if a person is buying open cows, or heifers that may have already been exposed to a bull, there is risk of bringing carriers into the herd.
“Anyone bringing in new cattle should pay attention to biosecurity, and trich is one of the diseases we need to worry about,” Waldner said. “We have good data showing that the PCR tests work quite well for checking bulls. The issue for most producers is how many times they should test each bull,” she said. Based on a single negative test result, there are only a few situations where you can be relatively certain that the bull is free of the disease. Some infected bulls won’t show up positive on just one test.
“One test does give you a fairly high degree of confidence in extremely low risk situations. For example, if the bull has been in your herd several years and has always had good pregnancy rates, and has not been exposed to any high-risk cattle, one negative test may be adequate. Also, a new yearling bull that has not yet bred any cows should be fine. One negative test on very low-risk bulls can give you a high level of confidence that those bulls will be clean,” Waldner said.
“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), then you’ll want more tests. 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 the neighbor’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 said.
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 negative results. “Another problem is inconsistency in what we get from the bull, and the number of organisms that are being shed when we take samples. These numbers can fluctuate over time, and between samples,” Waldner said. You have a better chance to identify the infection if you take repeated samples, at least a week apart.
“Nobody wants to put their bulls through the chute three times if they don’t have to, but sometimes there is good reason for doing it. In any high-risk situations, such as a breech in biosecurity, or history of open cows or abortions, you need to do enough tests to have a high level of confidence that a bull is free of infection before you use that bull again for breeding.”
Depending on the risk situation, and if you think your herd may have had contact with other herds or other bulls, it is wise to incorporate a trich test into your annual breeding soundness evaluation for bulls. “We don’t see a lot of trich here, but when it does happen it is a very serious problem, with extremely low pregnancy rates,” she said.
Recommendations for prevention 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. “Some of the wrecks I’ve seen have occurred in situations when producers had to quickly replace a bull that got hurt in the early part of the breeding season. Sometimes they end up borrowing a bull from a neighbor, or purchasing an older bull that is more likely to have been exposed to cows from different sources.
“Infected bulls do not show any symptoms. There may not be time to test that bull and have results back before you need to use him, but a sample should still be collected for testing, in high risk situations,” she said. Even if you have to pull him back out of the cow herd when you get the test results back, this is better than having him breeding a lot of cows through the rest of the breeding season, and infecting more cows.
“Some clinics use cultures for testing, rather than sending samples to a lab for PCR tests, to reduce costs for individual samples. 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 said. Also the results are faster than waiting for the results of the culture.
“Recently there has been more effort amongst the 18 western states to harmonize their import requirements for trich when cattle move between states,” Logan said. “Up until now there’s been differing rules in different states. We’re not completely synchronized yet on the rules, but we’ve made progress in getting more consistency.”
It’s difficult when animals going to state A need one thing, and when going to state B need something completely different to comply with import rules. “Obviously, each state has to be able to decide what it needs to do, to protect itself, but effort is still underway to get the rules to be more similar. We will be talking more about this at the upcoming Western States Livestock Health Association meeting in July,” Logan said.
His advice to producers at this point is to follow the recommendations and rules. “You could easily have trich in your herd and not be aware of it. There’s not always a sudden drastic reduction in pregnancy rates. Annual testing of bulls, at the least, is an important recommendation, along with sending open cows to slaughter only — so they won’t end up in someone else’s herd,” he said.
Continuing education about the disease is important. “Some producers, especially those who might be new to raising cattle, don’t always know some of the management things that are important, and may end up putting themselves and their neighbors at risk.” ❖
— Smith Thomas is a cattle rancher, horseman, freelance writer and book author, ranching with her husband near Salmon, Idaho. She can be reached at firstname.lastname@example.org.