Trichomoniasis is a subtle disease that can enter a herd without obvious signs — until the rancher discovers a high number of open cows at preg-check or observes cows returning to heat when they should have settled. “Trich” can be introduced when cattle share range pastures, or a fence breaks down and the neighbour’s bull gets in, or ranchers exchange or lease used bulls, or buy a non-virgin bull that has not been tested, or purchase open cows with unknown history.
Canada’s cattle industry is currently looking into requiring some testing, but has not yet implemented control measures. Sixteen western U. S. states have testing programs to reduce the disease, and at least two more states are developing control/testing programs. Idaho was the first state to require mandatory annual testing, beginning in 1989 but it took awhile before some of the other states followed suit.
Robert BonDurant, former professor of veterinary reproduction at UC-Davis (now retired), spent many years studying this disease. “We randomly sampled herds in California 20 year ago and at that time we found that 16 per cent of herds in our state had at least one infected bull. We tried to get California to follow Idaho’s model of required testing, but this met with resistance,” says BonDurant. Testing requirements in California were finally enacted in 2003, with a strengthening of the laws in 2007.
Tritrichomonas foetus, a one-celled protozoan, lives in the sheath of bulls and in the reproductive tract of cows, spread from animal to animal by breeding. The infection kills the developing embryo or fetus in the bred cow. She aborts during the first four months of gestation. After aborting, the cow becomes temporarily infertile. She returns to heat but generally does not settle if bred — until she clears the infection, which usually lasts 120 to about 150 days.
If an infected bull breeds cows, he passes the infection to them. If those cows are bred by another bull, he too will pick up the protozoa. If bulls are removed from the herd after a short breeding season (45 to 60 days), affected cows will be open because they did not have a chance to rebreed after losing their pregnancies. If bulls are left in for a long time, cows will breed back after aborting and recovering from the infection, producing late calves and a strung out calf crop the next year.
After the reproductive tract of the cow recovers, she generally has a natural immunity, which lasts about a year. A few cows may carry the disease over into the next year (if they got it toward the end of the breeding season) but bulls are the main problem in spreading trich because they tend to be carriers for a longer time.
Young bulls may spread the disease and then recover (throwing off the infection between breeding
Cattle that mix on range are at greatest risk of contracting Trichomoniasis which can really affect breeding success
seasons), but older bulls generally remain infected for the rest of their lives. Most young bulls are merely mechanical spreaders for a short time, whereas bulls over three years old do not get rid of the protozoa once they are infected. These bulls carry the disease to the next season, continuing to infect cows during subsequent breedings.
The protozoa thrive in airless conditions, and live in the tiny pockets or folds that line the inner surface of the sheath. The high infection rate in older bulls is due to the fact they have more folds in which the protozoa can survive for long periods. Carrier bulls begin infecting cows at the start of the breeding season, and greatly increase the chance for large numbers of cows being exposed to the disease.
“One of the things we learned while doing our research surveys is that not all positive cultures are actually trich,” says BonDurant. “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. But about 10 years ago we were seeing virgin bulls come up with positive tests, and no way to have gotten trich. We learned that there are some trichomonads that are not pathogenic, so we get some false positives,” he says.
Debra Lawrence, Idaho State Veterinary Medical Officer, says cattle producers in Idaho requested testing, beginning in 1989. At the start of the program, this disease was costing the cattle industry in Idaho close to five million dollars annually, in calf loss and having to replace open cows.
Idaho tests about 20,000 bulls a year. All bulls in Idaho used for breeding must be tested annually, and virgin bulls tagged. Any bulls coming into the state, no matter where they are going, must be tested before they enter.
Most western states require a trich test. There are also some grazing associations across the U. S. that try — through their grazing contracts — to manage the disease within their own associations.
The only “safe” bull is a virgin bull that has never had access to cows. Any bull that has ever bred cows should be tested, to determine whether he is free of trich. To test a bull, the veterinarian collects mucus cells from the deepest portion of the sheath (using a long, small diameter rod to enter the sheath and retrieve the mucus), then cultures this material to allow the trichomonads to grow and multiply. The culture is observed for three to seven days to see if there are any trichomonads growing. A heavily infected bull will have a positive culture within three days. If the culture is negative at that point, there is a good chance the bull is not infected, but the culture is watched for seven days to make sure no trichomonads show up. Any bull that tests positive should be culled and sold, but since there are a few false positives, a valuable bull that tests positive should have the culture sent to a lab that does PCR tests.
Bulls testing negative should be retested a week later if there is any suspicion that trichomoniasis might be a cause of problems in that herd, since the test from a culture is not 100 per cent accurate with a single sample. The test is 90 per cent accurate. This means that out of 100 positively infected bulls tested, only 90 will show up on the first test as positive. If any bulls in your herd test positive, the others should be retested a week later to make sure they are actually negative.
“The PCR test is becoming more affordable, and we can do it in our lab now, instead of having to send the samples to UC-Davis,” says Lawrence. “The turnaround time is much faster.”
If the disease gets into a herd, the cows will also have to be managed (by vaccination) in order to correct the problem, so the disease cannot be spread. A veterinarian can help a producer develop an effective vaccination program.
In range areas, where cattle herds run together on public land, or in any region where the disease exists and you don’t know the status of your neighbour’s cattle, control of trichomoniasis can be difficult without a co-operative effort among stockmen. Even if one producer eliminates trichomoniasis in his herd, there is always risk of infection from the neighbour’s bulls unless the neighbour, too, is testing and controlling the disease. If a bull is used for two breeding seasons (spring and fall, for instance) he should be tested twice annually, ahead of each breeding season.
There is no treatment for trichomoniasis; prevention is the only recourse. It is important to cull carrier cows and bulls.
Oregon State University Cooperative Extension specialists list these ways to keep a herd free of trichomoniasis:
1. Use only virgin bulls, or keep your bull battery as young as possible (keeping bulls for only two years, for instance).
2. Test all bulls that have previously bred cows.
3. Test all new bulls before putting them with cows, or purchase bulls from a breeder who has all bulls tested before being sold.
4. Use virgin bulls on virgin heifers.
5. Pregnancy test all cows and heifers 60 to 90 days after breeding and cull all those that are open. This eliminates most of the females that may have been infected and aborted and might still be infective to a bull.
6. In an infected herd, consult with your veterinarian, and vaccinate all females twice the first year, two to four weeks apart (with the second vaccination one to four weeks before the breeding season starts), and revaccinate all females annually.
7. Keep fences in good repair so herds don’t mingle.
8. Be suspicious about buying cows, especially cull cows. You may inadvertently introduce “trich” to your herd.
One key to using vaccine in cows is timing; immunity will be highest soon after vaccination. This applies with all reproductive diseases and not just trich. Too many people vaccinate for vibriosis or lepto in the fall at preg check time. Those vaccines won’t give immunity that long.
The other key is to reduce the number of carrier animals, if possible. The goal is to reduce the challenge and raise the resistance — those two factors together help control disease. The resistance factor involves using a vaccine at the right time, in a healthy animal with a good nutritional program that bolsters the immune system.
Heather Smith Thomas ranches with her husband Lynn near Salmon, Idaho. Contact her at 208-756-2841