Lee Jones, MS, DVM
Editor’s Note: Dr. Lee Jones is Assistant Professor/Vet Field Investigator at the Department of Population Health, University of Georgia College of Veterinary Medicine, Veterinary Diagnostic Lab, 42 Brighton Road, Tifton, GA 31793.
Trichomoniasis is a sexually transmitted disease in cattle caused by the protozoa, Tritrichomonas foetus. This single-celled, flagellated parasite lives in the preputial folds of bulls who serve as unaffected carriers of the organism. It is a significant cause of infertility and pregnancy wastage in cows. In the last 12 months two bulls have tested positive for T. foetus in GA.
Though bulls don’t show any symptoms of infection, they are carriers of the parasite; however, the negative clinical effects of infection are more significant in the female. T. foetus colonizes the epithelial crypts of the prepucial mucosa and does not invade the epithelium. These crypts or wrinkles deepen with bull age which provides a more favorable environment for the parasite and causes the chronic carrier state. Young bulls (less than 3 years old) that breed infected cows are more likely to have a short term infection and less likely to develop into carriers. Though some studies have shown slight breed predilections, no clear breed associated susceptibility has been established. Infection with T. foetus has no effect on bull fertility and the parasite is not detected during a routine fertility exam. There is no effective treatment for infected bulls and bulls that test positive for T. foetus must be sold for slaughter only.
Cows are infected during breeding by an infected bull. Infection in the cow usually results in early fetal death, abortion, infection or infertility. Fetal death most commonly occurs by 50-70 days after conception. Clearance of the infection by the cow is variable and infection often results in a longer calving interval of 90 days or more. In rare cases pregnant cows may carry the organism and be a source of infection after calving. Veterinarians from Colorado State University labeled the insidious disease ‘the silent rustler’. Farmers may suspect trichomoniasis in their herd if they have an increased percentage of non-pregnant cows, increased percentage of cows bred late in the controlled breeding season, abortions especially less than 3-4 months of gestation or increased number of dead fetuses at pregnancy check (easily diagnosed with ultrasound).
A number of states have enacted more stringent testing requirements regarding the importation of bulls greater than 18 months of age. Some states have also implemented regulations restricting the transfer of ownership of non-virgin bulls within their states. In a 2004 report, 30% of the beef herds tested in FL had at least one bull test positive for T. foetus. A 1994 report found a prevalence of less than 1% in Nebraska and Colorado but by 2008 there were 311 bulls that tested positive in 21 counties in NE.
Reproductive efficiency is essential to herd profitability. Trichomoniasis can have a severe financial impact in infected herds by reducing reproductive efficiency through delayed conception, embryonic loss and abortion, which is intensified as bull infection prevalence increases. Economic losses also include increased number of non-pregnant cows and culling of infected bulls and open cows, fewer and lighter calves at weaning, veterinary costs of testing, and cost of replacing bulls and open cows.
The effects on herd production are similar to those of infection with Campylobacter foetus, Leptospira hardjo Ureaplasma, nutritional deficiencies relative to drought or poor management and using infertile or sub-fertile bulls. An investigation to identify the cause(s) of poor reproductive performance in herds must be comprehensive and include careful inspection of management practices, cow herd health and bull fertility. Diagnostic testing for the presence of T. foetus involves obtaining samples of prepucial fluids from all bulls in the herd and has to be performed by a qualified veterinarian. There is no blood test to test for the disease.
Treatment and Control
There are no approved treatments for cows or bulls infected with T. foetus. A vaccine is available for cows but it does not provide protection from infection with T. foetus. The vaccine requires 2 doses, 2-4 weeks apart, with a single, annual booster each subsequent year 4 weeks prior to the breeding season. The vaccine reduces the severity and duration of the disease.
When T. foetus has been confirmed, all bulls should be tested and any positive bulls should be culled. Three sequential, negative tests taken one to two weeks apart are required to declare a bull clean. Annual follow up tests on all bulls are recommended. Removal of all open cows and careful screening of other high-risk, late calving cows is also recommended in herds with trichmoniasis. Management practices that perpetuate this disease include keeping infected bulls in the herd and purchasing infected bulls or cows.
Implementing a biosecurity program is the best course of prevention. Purchase only virgin breeding stock for replacement animals. Also, using a controlled breeding season and culling all open cows after pregnancy diagnosis helps minimize the risk of reproductive diseases in herds.