NEWSLETTER ARTICLES

Livestock and Natural Resources

What is Trichomoniasis?
It is a disease of cattle that causes infertility, open cows, and occasional abortions in cows and heifers. It is commonly referred to as "Trich," and is a disease that can be economically devastating for infected herds. Trichomoniasis can also be costly to eradicate from a herd.

What causes Trichomoniasis?
A protozoan, called Tritrichomonas foetus is the microbe that causes this condition. It is similar to, but not the same as, a venereal organism in humans called Trichomonas vaginalis. The cattle organism lives in the microscopic folds of the skin that line the bull’s penis and internal sheath. As the bull gets older, this skin grows and folds more and more, creating additional places where the organism can thrive. Therefore, older bulls (more than three years of age) are more likely to become chronically infected with the "Trich" organism than younger bulls. In the cow or heifer, the organism lives in the cavity of the vagina and uterus until her immune system eventually destroys it. That destruction process (immunity) may not occur for 3-20 weeks. Also, the immunity is short-lived, so a cow or heifer can become infected again.

What are the signs or symptoms of "Trich" in cattle?
Neither the cow nor the bull appears ill at any time when they are infected with this organism. The cow, after having been infected at breeding, may rarely show a very subtle, very mild vaginal discharge, 1-3 weeks later. Most of us would never notice it. The bull rarely shows any indication that he is infected. So, there are no outward signs that the bulls, cows, or heifers are infected with "Trich."

What if Trichomoniasis gets into my herd?
If it is a new infection, i.e., if your herd has never been infected before, you can expect a long, drawn-out calving season, with a disappointing total calf crop. In such herds, it is common to end up with a 50-79% calf crop, strung out over 3-8 months. If the herd has been infected for a long time, the effect may be slightly less. That is, a higher number of cows will get pregnant, but never as many as normally would calve if there were no "Trich" present. Because "Trich" often gets into a herd via the introduction of one infected animal, especially an infected bull, another scenario is possible. In this case, after the first year, the percentage of pregnant cows may fall from 95% to 90%, for example. In the second year, there may be a further fall to 75% or less, and a problem will be obvious.

The reason for the open or late cows is the fact that the Trichomoniasis organism causes the loss of the calf a few weeks into the pregnancy. A few cows in the herd (perhaps 5%) may actually abort due to "Trich," nearly always before five months’ gestation. However, many factors are involved in abortion, and Trichomoniasis is just one factor, and a less common one at that. So don’t assume that every abortion is a sign of "Trich." A few cows (perhaps another 5%) may develop pyometra, i.e., a heavy, pus-filled uterus, after being infected. A qualified veterinarian can detect this pyometra at pregnancy check time. Cows or heifers with pyometra at the time of pregnancy check (as opposed to after calving) should make you very suspicious about Trichomoniasis.

It can, but most cows do not abort a fetus big enough to find. Instead, they come back into heat at some extended interval (usually more than 21 days) after breeding. Most cows will eventually settle, if given enough time, but their immunity to the disease is weak. They can be reinfected the next season. What apparently happens when a "clean" cow is bred by an infected bull is that her egg is fertilized, but the disease organism either kills the embryo soon after conception, or the uterus’ reaction to the "Trich" organism kills the embryo. In either case, the cow or heifer may not lose her "conceptus" until the end of the breeding season.

How is Trichomoniasis transmitted?
Trichomoniasis is a venereal disease of cattle (all breeds). It is transmitted from cow to cow by a bull, so it is nearly always a disease of cattle that are naturally bred, as opposed to those cattle bred by AI. Very rarely, it can be transmitted by contaminated semen or AI equipment, but this is highly unlikely if semen is purchased from reputable bull studs and hygienic artificial insemination methods are used. Like most venereal diseases, there is only one way to contract Trichomoniasis... that is by sexual contact with an infected mate. There are rare cases of a cow or heifer being infected by contaminated semen or AI equipment, but these are not generally important means of spreading the disease. Reputable AI studs take great pains to assure that their product (bovine semen) is free of Tritrichomonas foetus.

How common is Trichomoniasis in cattle?
Bovine trichomoniasis has been, and continues to be, an important cause of economic loss in cattle operations that use natural service. In the Western U.S., where extensive grazing (vs. intensive grazing on permanent pasture) management practices are employed, the disease is prevalent at surprisingly high rates. In 1990, a random survey of California beef cattle operations revealed that more than 15% of herds were infected (i.e., they had at least one infected bull). Several factors such as grazing associations, renting or borrowing bulls, large areas of common fence lines, etc., favor introduction of "Trich" from one herd to another.

How can I tell my herd has it?
In spite of the fact that bulls don’t show any signs, the organism is easier to find in bulls than in cows, because bulls become "carriers" while cows eventually shed the infection. Special culture media have been developed that can support growth of the organism in an incubator. Scrapings of preputial (internal sheath) fluids are taken and placed in this medium, which is then cultured for up to a week. If even one bull is positive, you have to assume that the herd is infected.

Is the diagnosis a sure thing?
No, but the technique used is quite good, as diagnostic tests go. Studies of known "positive" bulls have shown that the culture method (described above) will miss about 10-20% of infected bulls if we only test them once. But testing the herd (all the bulls in the herd) once gives us an 80-90% chance of finding the disease if it’s there. If no infected bulls are found on the basis of a single culture of all bulls, then we can be 80-90% sure that the bull herd is "clean." Repeat testing (up to three times, at weekly intervals) is necessary if we want to be more than 99% sure that the entire bull herd is negative. It’s important to give the bulls 1-2 weeks of sexual rest before beginning to test them for Trich. This allows time for the numbers of organisms to build up to a level that can be detected.

You can begin to see why Trichomoniasis is such a difficult disease to eliminate once it establishes itself in a herd. Remember that the infected bull(s) that is showing no evidence of disease is the main means of transmission. Also, cows or heifers that become infected can spread the organism to uninfected bulls during breeding. Therefore, some cows in the herd can be a source of the organism for other members of the herd prior to the time those individual cows clear the "Trich" organism from their reproductive tract.

Is there a treatment for the bulls?
Technically, ethically and legally, no. There is no FDA-approved treatment for "Trich" in cattle. Several years ago, some bulls were successfully treated with a poultry product, but the drug is not approved for such use in cattle. Not only that, but the FDA has declared that the use of this poultry product in cattle is outright illegal.

What about the cows and heifers? Most studies have shown that the disease is self-limiting in the female. This is in contrast to the bulls, who can carry the "Trich" organism for years. After several heat cycles, most cows and heifers clean themselves up, but this may take months. Research is showing that up to six months may be required in some cases, but 1-4 months is more common.

Is there a vaccine?
Yes. Fort Dodge currently markets a vaccine made from killed whole cells of Tritrichomonas foetus. Tests of this vaccine have shown that experimentally infected, vaccinated females "clear" a vaginal infection in a matter of a few weeks, whereas control (unvaccinated) females can remain infected for months. As of this date, no efficacy for bulls has been shown, i.e., the vaccine has not been shown to protect bulls from becoming infected. Also, vaccination of the bulls with the "Trich" vaccine will not eliminate the organism from the bulls.

At pregnancy check time, non-pregnant females, especially those with reproductive tracts that the veterinarian declares "abnormal" (e.g., with pyometra) should be sold for slaughter. Do not keep these females. They might represent "carrier cows" that could maintain the disease in the cow herd even if the bulls were cleaned up. Non-pregnant females with "normal" tracts may be kept over for re-breeding if a "split" calving season is practiced. However, some of these open cows that feel normal may be infected with "Trich" for weeks to months. They should not be mingled with the normal, pregnant cows, nor should the same bulls breed these two different groups of cows. Alternatively, these open cows could be culled. It is important to understand that some cows in a herd with "Trich" could be a source of re-infection of that herd in the months after discovering the infection. Additionally, in some herd situations, artificial insemination can be used to clear up an infected herd and heat synchronization can be helpful in this regard.

What are some of the steps to prevent Trichomoniasis?
There are several practices you can do to protect your herd:
Use young, fertile bulls (<3 years). Many studies have confirmed that younger bulls are less able to carry and transmit the disease. That is, younger bulls are more resistant to the "Trich" organism and are less likely to transmit this agent to the cow herd. Purchased bulls should have a breeding soundness examination, including a semen check, and a "Trich" test to be sure they are healthy and free of disease.
Keep fences in good repair. Good fences make good neighbors.
Culture new bulls and old bulls prior to the breeding season at the semen exam time. This is also a good time to vaccinate bulls for Vibrio, another venereal disease.
Be very suspicious of new cows or bulls, especially somebody else’s cull. Keep the cow herd closed and use only virgin and/or "Trich-negative" bulls whenever possible. Do not loan, rent, or borrow bulls.
If there is some risk of Trichomoniasis entering your herd, vaccinate females for "Trich," twice at 1-month intervals, then give annual boosters. The best time to vaccinate (or to give annual boosters) is just a few weeks before the bulls are turned in, so that immunity in the cows is high at the time of possible exposure to the "bug." It should be noted that if there is no risk of introduction of "Trich" to a closed herd, vaccination will not be necessary.
If cattle are run on open range, where there is a risk of introducing "Trich" into the herd, it may be advisable to adjust the breeding/ calving season so that the cow herd is pregnant when they go onto range. No breeding, no risk of "Trich."
Trichomoniasis is a complex disease problem, and your veterinarian should always be consulted regarding decisions about preventing, controlling, or diagnosing this disease.