Trichomoniasis, A New Challenge
Dave Sparks DVM, OSU Area Extension Quality and Health Specialist
Trichomoniasis is not a new disease but its prevalence has increased dramatically in recent years, mostly due to the increased movement of breeding stock from region to region. Commonly called Trich, it is a highly contagious venereal disease that causes infertility and abortions.
Trich is caused by the protozoan pathogen Tritrichomonas foetus, which can live in the cow's reproductive tract and on the surface of the bull's penis. This organism has a close cousin, Tritrichomonas intestinalis, which lives in the intestinal tract and causes no problems. It may however be picked up in testing, causing a false positive, if fecal material splashes onto the penis. There are no apparent signs of sickness in animals infected with Tritrichomonas foetus, but the herd will have too many open cows, abortions, extended calving season, and in a few cases uterine infections. The bull serves as a mechanical vector to spread the disease within the herd. In some younger bulls the infection may clear itself in time if the bull is not reinfected by breeding more infected cows. In older bulls the microscopic crypts in the prepuce, or sheath, become deeper and the organism establishes itself deep within these crypts, resulting in chronic infections. Most bulls aged 4 years or older, and some 2 and 3 year old bulls, develop chronic infections which cannot be cleared. Slaughter is the only viable alternative for these bulls. Cows are infected at breeding. 80% to 90% of the cows served by an infected bull will become infected. After failing to establish a pregnancy for several cycles, the cow can develop a temporary immunity and maintain a successful pregnancy to term. This results in an extended calving season if the bull is left on the cows with resulting small light calves at weaning. If the bull is put with the cows for a limited breeding season, the results will be a poor pregnancy rate and too many open cows. This immunity is short lived, however, and the cow is susceptible to another course of the disease in the following year. Some herds, in fact, experience relatively mild problems in the first year but have a real reproductive calamity in the 2nd year.
Trich is diagnosed in the bull by testing at least 2 weeks after he has done any breeding. The veterinarian washes material from the penis and sheath of the bull for the lab to culture in order to see if the organism is present. It takes from 5 to 7 days to run the test. Unfortunately, one test does not always tell the true story. If you have multiple bulls one test on all the bulls may serve as a screening tool to determine if the disease is in your herd. For regulatory issues such as bulls going out of state, most states will require 3 consecutive negative cultures. An alternative is the PCR test. Although this test is more expensive, reliable and acceptable results can be obtained with one test. The PCR test also has the ability to differentiate between the pathogenic Tritrichomonas foetus, and the incidental contaminant Tritrichomonas intestinalis. If cows are to be tested, the test is run on vaginal mucous 10 to 30 days post breeding. In the cow, 5 negative cultures are required to say conclusively that she is not infected.
Prevention of trichomoniasis requires a multilevel approach. The first step is to test the bulls in your herd and slaughter the positive animals. Using young bulls will help to prevent chronic infections. When you acquire new bulls buy virgin bulls from reliable sources. If new additions are not virgins, or if their past breeding status is unknown, test them with the PCR test. The incidence in cows can be reduced by using a short breeding season and culling open cows. There is a lot of wisdom in the old saying that good fences make good neighbors. Prevent comingling with neighboring herds to prevent passing this and other venereal diseases back and forth. A vaccine is now available for prevention. Two vaccinations are required to start the program. These vaccinations should be given 4 weeks apart and concluded 4 weeks before breeding season. Subsequent single annual boosters are required. While this will help to minimize losses when used in the cows, it will not clear chronically infected bulls or prevent bulls from becoming infected if they breed an infected cow.
Regulations differ from state to state, they all require testing for Trich unless the bulls are going to slaughter. Some states allow virgin bulls to enter if accompanied by a veterinarian's certification. It is hard to determine how widespread the problem is in most states.
Your local veterinarian is your best source for more information. He will be able to help you assess the risk factors in your area and within your herd, and suggest appropriate prevention steps that fit your operation effectively and economically. He will also know where to go for current answers to the continually changing regulatory questions.
Dr. Rick Rasby, Professor of Animal Science
Animal Science, University of Nebraska - Lincoln, Lincoln, NE