Cattle Today

Cattle Today

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By: Heather Smith Thomas

Trichomoniasis is a subtle disease that can sneak into a herd without obvious signs, until preg check time unless you observe cows cycling through summer when they should have been settled. This venereal disease can occur when ranchers don't have a closed herd or use untested bulls as when cattle herds run together in common pastures, fences break down and the neighbor's bull gets in, ranchers exchange or lease used bulls, or buy any non virgin bull that has not been tested.

The disease is caused by a one celled protozoan that lives in the sheath of bulls and reproductive tract of cows. The animals are not sick, but the infection kills the developing embryo or fetus within the first four months of gestation. The cow returns to heat again but generally does not settle until she clears the infection and becomes fertile again after two or three more heat cycles.

In a short breeding season where bulls taken out after 45-60 days, affected cows will be open at preg check time because they did not have a chance to rebreed after losing their pregnancies. If bulls are left in, cows will breed back late after aborting and recovering, producing late calves in a strung out calving season.

A few cows may carry the disease over into the next year, if they became infected late in the season, but bulls are the main problem in spreading it because they tend to remain carriers.

Young bulls may recover after a period of rest (overcoming the infection during the months they are not used for breeding), but older bulls often remain infected for the rest of their lives. The protozoa live in the tiny pockets and creases that line the inner surface of the sheath. The high infection rate in older bulls may be due to the fact they have more folds in which the protozoa can survive for long periods.

Idaho was the first state to initiate mandatory annual testing of bulls (in 1989). About 20,000 bulls are tested each year in Idaho and in the first year of testing, 325 bulls were found to be positive. Since then, there has been a 91 percent reduction in positive bulls in the state, and an 85 percent reduction in positive herds. Utah has a formal testing program, similar to that of Idaho. Oregon has a program and Colorado is in the process of developing one. Wyoming and Montana are also considering it. There are a number of other states that realize they have a problem but as yet have no formal testing programs. There are some grazing associations (in those states without test programs) that try to manage it within their associations, with bull testing.

Dr. Bob BonDurant (Professor of Veterinary Reproduction, School of Veterinary Medicine, University of California, Davis) says the disease is widespread, but we don't know the actual numbers. "It is not just a western problem. Florida certainly has it, and it has also been reported in Missouri and several other states in the last four or five years. If we look hard enough, we find it. It is not a mandatory reportable disease, however, so we don't know the actual prevalence. We randomly sampled herds in California, but that was more than 10 years ago. At that time we had a 16 percent infection rate; 16 percent of herds had at least one infected bull."

"We are trying to get California to follow Idaho's model in terms of required testing, but this is meeting some resistance. Some cattlemen don't want mandatory testing for anything what they perceive as the government interfering in their business. The legislature has the authorization (which has been given to them by the California cattlemen and by the California Department of Food and Agriculture) to go ahead and write legislation, but just what that legislation will be, we don't know yet but I don't see how the program can work without mandatory testing," he says.

"They are considering voluntary testing, with mandatory reporting.      In other words, if you test and are positive, they report it to your neighbors. That is likely to make it so nobody tests. We're trying to talk them out of that type of program."

"It would be good to have the national cattle organization petition NAHMS (National Animal Health Monitoring System, under USDA) , to survey for trichomoniasis. Every year they survey parts of the livestock industries in the country to determine the prevalence and impact of specific diseases and conditions. It might be dairy cattle one year, pigs the next, etc. The next time beef cattle roll around, I would hope they would add trichomiasis to their list of things they survey for. Then we would get a national, accurate impression," says BonDurant.

"One of the things we've learned in doing these surveys is that not all test positives are actually trich. We used to think that if you cultured the bull and got something in the culture that looked like a trich and swam like a trich, it was trich. We're learning now there are some false positives: there are some trichomonads that are not pathogenic. So there are a few false positives as well as false negatives, on these tests," he says.

"If a bull has trich and you take a sample and culture it and use what most people use to culture with - you have about a 90 percent chance of finding it. That's not bad. But that means there's still a 10 percent chance that an infected bull got by you. We suggest you run them through again a week later and retest. If they all come up negative again, you've now got 10 percent of 10 percent or only one percent chance of a false negative. If you do it a third time, you're down to 1 in 1000, so you've caught whatever is there, " he explains.

"If you've ever had trich in your herd or you think it's in the neighborhood or grazing association, we strongly urge people to test their bulls three times, at weekly intervals. It's a nuisance, but it certainly saves having a poor calf crop the next year. Once you get trich, it's tough to deal with," says BonDurant.

"The 90 percent sensitivity of the test is well documented, but the specificity of the test how many false positives you might get is another story. We didn't think we had any, until about three years ago. We were seeing virgin bulls come up with positive tests, and no way to have gotten trich. It turns out the 'bugs' we got from the prepuce of virgin bulls are not Tritrichomonas foetus, but a different trichomonad, and probably any one of several. There's a whole family of them. They are probably trichomonads that normally live in the gastro intestinal tract of the bull. These young bulls ride each other and get manure in the prepuce, and that's probably how they get contaminated," he says.

"We started finding those and with the kind of microscopes we use out in the field, we would mistakenly call them trich. It's only when you have an electron microscope or some other powerful tool      (that most people don't have) that you can tell the difference. Now we are using some DNA testing, so we can be more accurate. We are trying to develop a two step diagnostic process; your vet is the first step, coming out to culture the bull. If it's negative, fine. If it's positive, we recommend they send it off to a lab to confirm it by one of these other tests, like DNA. This will probably require some sort of certification for the labs that will run that confirming test. Most people won't have to go to that step, because most tests will be negative," he says.

"This is a way of protecting the bulls. We don't want to send bulls to slaughter that don't have trich. You can imagine the loss that would be, with an expensive bull, if he comes up with a false positive. You don't sleep well if you think you've sent one of those to slaughter! So this is what we are recommending, and trying to get accepted by the industry, starting here in California. We are working with 9 or 10 diagnostic labs from the western states, and they are sending us their positives, and we are running this DNA test," says BonDurant.

"We can learn a few things this way. The most important thing is whether the bulls are truly positive or not. From a scientific standpoint, however, we want to know more - not just what the bugs aren't, but what they are. So we will eventually learn that, as well. I don't think these are pathogens. We've only had a chance to study one type of these non specific trichs; we grew them up and put them into some virgin heifers, and they didn't cause a problem. If fact, they couldn't even sustain an infection. So at least that group is not pathogenic. We have a USDA grant now, to work with the western states, to take their positives and characterize them with our DNA testing to try to determine if any of these others could be pathogenic."

"Currently the only vaccine available in the U.S. for cows is a killed, whole cell product. They grow the organism in very large cultures, kill it, and disperse it in an adjuvant, which helps boost the immune response. It's similar to lepto vaccine, for example, which is also a killed, whole cell product. They used a California isolate to make the trich vaccine," he says.

"It's hard to answer the question as to how effective the vaccine is; there's only been one really good study done, at the University of Nevada, a few years ago, by Dr. Kvasnicka. In that study, the vaccinated cows when they were exposed to infected bulls had a significantly higher calving rate the next season than the non vaccinated cows," explains BonDurant.

For best results, the cows must be vaccinated twice the first year, with two injections given two to four weeks apart, the second dose given within one to four weeks ahead of breeding. "If you get them vaccinated just before exposure, they are better protected. This disease has a notoriously short lived immunity," he says. Natural immunity after a cow recovers from the disease is only a year, at most, and generally less.

"With vaccine, the length of immunity is even less. If you vaccinate cows at weaning time, when the pregnant cows won't be exposed to the bulls for several more months (after calving), their immune response has waned too much. It's best to do it much closer to breeding, with the second vaccination about a week before the breeding season starts. Following the initial vaccination, it takes three to four weeks to make a good immune response, but following the booster, it takes about 10 days. The cow would thus have her maximum immune response about the time she is being bred. If you use the vaccine by the label instructions, it's a reasonable vaccine. You'll still have some abortions if there are infected bulls running with those cows, but you won't have as many abortions as you would with unvaccinated cows," he says.

"In the Nevada study, the vaccinated cows were exposed to infected bulls, but to be sure they were really challenged, the researchers artificially put another 10 million organisms into the vagina of each cow. That's a whopping dose probably more than any bull would put in there so they would all be challenged. Even so, their calving rate was double the calving rate of the nonvaccinated controls. The controls had a 30 percent calving rate; the vaccinates had a 60 percent calving rate. None of us would want to make a living on a 60 percent calf crop, but you have to consider that these cows were given a massive challenge probably more than would occur naturally. Under normal conditions, they might do better. It's not a perfect vaccine (no vaccine is perfect), but it is better than nothing," he says.

"I tell most of our clients that if they've never had trich and no one in their neighborhood has ever had trich, and everyone checks bulls before the breeding season, there's probably no need to vaccinate. It's pretty expensive, and only a so so vaccine, but I would recommend using it if there's any history of it in your own herd or in the neighborhood or you are bringing in bulls that had bred cows elsewhere anything that increases the risk of exposure." The first year, every cow should have two doses, and an annual booster in following years.

Older bulls are more apt to carry the infection than younger ones. "The older bulls have more folds in the epithelium of the sheath, providing nice little niches down in those creases for the protozoa to live. There are some drugs which in the laboratory (in a test tube or petri dish) will kill the trich nicely. They are safe drugs and you'd think they would work well. But if you try to treat a bull, they don't work. We've tried different compounds, but we can't get the drug to the proper locations. Some are not injectable; we'd have to give them locally in some type of infusion. We worked with a company in Scandanavia that specialized in surface active agents, like soaps, and foaming agents like shaving cream, etc. like shaving cream in a very high pressure can. We dispersed the drug (we tried several different drugs, different times) in that shaving cream like base and put it in the prepuce under high pressure, to push it down into those folds and creases, but we couldn't cure even one bull. That leaves us with no means of treatment." So prevention is the only route.

"One of the things we stress: if you are having bulls checked for breeding soundness, semen tested, etc. this is a good time to do the trich test. We don't want people to forget about vibrio (the other common venereal disease) but there's a vaccine that's very well proven for it for both the bull and the cow whereas the trich vaccine is only for the cows."

Trich can sneak up on you. You never see a sick bull or a sick cow. It's not until preg check time when it's too late that you find out you have it. Bulls are shipped everywhere these days, and the risks are increased for getting it. "That's how I got involved with this research, when people were shipping bulls between California and Idaho in the early 1980's. It was a big mess, with lots of finger pointing some people thinking the problem came from Idaho, some thinking it came from California."

We don't know where the disease came from in the beginning. "The causative organism, Tritrichomonas foetus, is the same bug as Tritrichomonas suis, in pigs. We don't know if it causes pathology in the pig, but it was first isolated from a pig from the GI tract and throat area (upper respiratory region). How did it get from pigs to cattle? We don't know. And in the last two years this same bug has been isolated in cats with diarrhea, from the GI tract. We know it's the same bug because we've done DNA tests on it. It could be there are different strains that affect pigs, versus cattle, versus cats but they are all the same genus and species. That took us by surprise." This broadens the opportunity for how it might have become established accidentally in cattle and found an environment in the bovine reproductive tract and became very well adapted to that environment.

The disease is probably becoming more widespread (we hear of cases in other states) and it would be nice to know how prevalent it is, rather than thinking of it as someone else's problem. If a producer suddenly ends up with a poor calf crop, trich should be one of the first suspicions.

"My colleagues in Europe give me a bad time about my work with trich. They feel it is an old fashioned disease because they got rid of it 50 years ago. But that's because they use artificial insemination. They don't understand why we can't do that, too. It's not until you bring them out here and show them what the American West looks like, that they realize AI is not really practical under most circumstances."

SIDEBAR: BULL TESTING - To be safe, any bull that has been used for breeding should be tested. Virgin bulls that have never had access to cows are not infected. To test a bull, the veterinarian collects secretions and cells from the deepest portion of the sheath (using a long, small diameter hollow pipette as used for A.I.) to enter the sheath and retrieve the material, then cultures this material to allow trichomonads to grow and multiply. The culture is observed for three to seven days to see if any are growing. An infected bull will usually show positive within three days. If the culture is negative at that point, there's a good chance the bull is not infected, but the culture is watched for seven days to make sure no trichomonads show up. Samples can be taken for culturing at the time of routine pre breeding fertility exams. If a bull is used for two breeding seasons (spring and fall) he should be tested twice annually, ahead of each breeding season.


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