A new wrinkle shows up in the diagnosis of one of the most confounding of all cattle diseases — trichomoniasis.
David Voldseth, Martinsdale, MT, knew something was wrong last fall when he pregnancy checked and found 25% of his cows open.
In pregnancy checking the year before, he'd found a group of cows that hadn't bred up quite as well as they should have.
“We just chalked it up to poor nutrition or something else,” he says. This time, however, he knew it was serious and suspected trichomoniasis — commonly called trich.
Voldseth has long vaccinated his cows for trich, so he thought his cattle were protected.
“Apparently, the challenge was so great and came about so early in the season that the vaccine couldn't overcome the disease,” he says (see “Biology Vs. Biosecurity,” page 32).
Now Voldseth is following recommended trich control procedures. He's culled all bulls more than 3 years old and is selling all dry cows. This spring, he plans to breed his cows at “home” before turning them out on the forest in late July. He'll also continue to vaccinate.
Caused by a protozoan (Trichomonas foetus), trich is a venereal disease spread by bulls. With no visible sign, it causes abortion and leaves cows infertile. (See “Trich Questions” page 33.) It can spread through a herd like wildfire — especially because it's difficult to spot.
For Voldseth and other Western cattle producers, trich diagnosis has just become more difficult, thanks to the emergence of another organism — Trichomonas intestinalis. This organism is thought to be non-pathogenic, says Arnold Gertonson, Montana's state veterinarian.
T. intestinalis appears nearly identical to T. foetus in the routine InPouch exam conducted by most vet labs. As a result, the threat of a false-positive disease diagnosis is becoming more of a possibility.
“Most labs can't differentiate T. intestinalis from T. foetus,” says Gertonson. “It's only going to be found through a polymerase chain reaction (PCR) test.” This additional test costs producers another $20-30/head and a week or two in turn-around time.
“If you get a trich-positive via the InPouch test, I'd definitely have it confirmed by a lab through a PCR test before you sacrifice the bull,” he says.
Most often trich isn't identified until it's too late and all other causes of infertility are ruled out, says Bill Kvasnicka, University of Nevada-Reno Extension veterinarian.
Several Western states have mandatory trich management programs, but little progress has been made in its elimination. While the disease seems to come in cycles, the threat still exists anytime a bull crosses a fenceline.
“We run in several forest allotments, and it's big country out here,” Voldseth points out. “It's almost impossible to keep cattle from getting mixed up.”
T. intestinalis thrives in the intestine of cattle, contaminating the sheath and penis through splashing manure. When swabs are taken for the InPouch test, T. intestinalis can be picked up with or without its cousin.
So far, Gertonson says T. intestinalis has shown up in tests from Colorado, California and Montana. But, it could be causing false-positive diagnosis anywhere trich is suspected. And, while a false-positive test is a problem for any rancher, a false-positive could spell disaster for a seedstock producer.
“You certainly don't want to be de-populating a herd of high-priced bulls based on what could end up being a negative test,” explains Marc Bridges, executive secretary of the Montana Department of Livestock.
Even the perception there might be trich in a herd could spell trouble for a purebred producer. “Either by causing him to de-populate bulls, or if word got out he had trich in his herd,” says Bridges.
Also, a false-positive test can be a problem for ranchers in states with trich testing requirements for bulls turned out on common or public grazing pastures.
“For example, in Idaho, in order to turn out onto Bureau of Land Management allotments, you need a trich test,” says Gertonson. “If you get a positive, you can't turn out — unless you confirm it's not T. foetus — those delays could cause some real problems.”
The trich vaccine will not work on T. intestinalis, Gertonson says. “It's a different bug altogether.”
For now, Western ranchers will have to live with the threat of trich.
“We'll just have to fight it with the knowledge and tools at hand,” says Kvasnicka. “It might not be easy, but if a producer really wants to eliminate this disease, it can be done.”
Biology Vs. Biosecurity
Bill Kvasnicka, University of Nevada-Reno and Nevada's Extension veterinarian, believes the cyclical nature of trich has less to do with biology and more to do with human nature.
“People tend to become complacent, letting their biosecurity slip for a year or two,” he says. “There's no other reason for trich to be so cyclical.”
Part of the biosecurity against trich is the use of young bulls, adds Kvasnicka. “People in trich-prone areas tend to keep bulls too long. Any bull over four years old is going to be suspect.”
There's a vaccine to protect cows, and there's excellent data supporting the efficacy of the vaccine, Kvasnicka says, “but it's critical that it be used at the right time in the right way.” Some ranchers use the vaccine in the fall at pregnancy checking but fail to give a second vaccination in the spring before breeding.
The vaccine was developed 10 years ago after Western ranchers who had dealt with the trich threat for decades pressed for additional tools to fight the disease.
A 1990 survey of California beef cattle operations revealed 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 and large areas of common fence lines — favor introduction of trich from one herd to another.
BEEF recently asked Bill Kvasnicka, University of Nevada-Reno and Nevada's Extension veterinarian some questions about trichomoniasis.
Q: What's the trichomoniasis disease cycle?
A: The organism lives in microscopic skin folds lining the bull's penis and internal sheath. As the bull ages, the skin folds increase, creating additional places for it to thrive.
Trich is transmitted to the cow where it causes vaginal/uterine infection and impedes fetal development. The cow's immune system will eventually destroy the organism. The immunity is short-lived, so a cow or heifer can become infected again. Some cows never completely clear themselves of trich, becoming persistent carriers.
Q: What are the signs or symptoms in cattle?
A: There are no outward signs when bulls or cows are infected. Cows or heifers with pyometra (a heavy, pus-filled uterus) at the time of pregnancy checking should make you suspicious about trich.
Q: What's the initial diagnostic step?
A: Scrapings of internal sheath fluids are taken from the bull, placed in a culture medium in the InPouch test for up to a week. This technique can miss some infected bulls if they are tested only once. Repeat testing (up to three times, at weekly intervals) is necessary to be sure the entire bull herd is negative.
Q: How can a producer keep this disease out of a herd?
A: Be careful about using older bulls. If you suspect a problem, use young bulls (less than four years). In addition:
Practice good biosecurity measures, including keeping fences in good repair.
Test new bulls at purchase or buy only tested bulls with a certification of a negative test. Then hold the bull in quarantine for a couple of weeks and retest.
Test all bulls two weeks after the end of the breeding season.
Try to keep bulls in clean pastures. Dirt and manure will contaminate the InPouch liquid media, compromising the diagnostic accuracy.
Be careful about commingling with cows outside your own herd, especially somebody else's culls.
Vaccinate all females for trich, twice at one-month intervals, then annually. The best time to vaccinate is a few weeks before the bulls are turned in, so immunity is high at the time of possible exposure.