Source:
by: Russ Daly, Professor, SDSU Extension Veterinarian, State Public Health Veterinarian
Reproductive success for a cow-calf herd depends on the optimal convergence of many different factors during the breeding season, including bull fertility, cow nutrition, and environmental influences, as well as pressure from infectious diseases that adversely affect the cow’s reproductive tract or the developing fetus. The harmful effects of many of those infectious diseases can be effectively prevented by vaccinations, but one reproductive disorder – trichomoniasis – mostly eludes the protective effect of vaccines and treatments.
What Causes Trichomoniasis?
Trichomoniasis in cattle is caused by a protozoal organism that lives indefinitely in the sheath of the infected bull. Once it’s transmitted to a cow or heifer through the act of breeding, it causes an inflammation in the female reproductive tract that results in the eventual loss of the pregnancy.
The outward appearance of trichomoniasis in an individual female depends upon how quickly that inflammation proceeds relative to the development of the pregnancy. When the inflammation occurs rapidly, it prevents the embryo from becoming established in the uterus, resulting in a regular return to estrus. At the other extreme, inflammation that progresses more slowly might not affect the pregnancy until the fetus has reached several months of gestation, causing an abortion. Pregnancy loss can occur any time along this continuum; irregular returns to estrus are commonly noted in trichomoniasis-affected cattle as well. Another feature of trichomoniasis in some affected cows is that of pyometra, or a pus-filled uterus in place of a fetus.
Taken together, these individual cow effects manifest themselves in a herd as open cows come pregnancy-check time (when short breeding seasons are employed) or as spread-out pregnancies if bulls are kept out longer. Following their exposure, cows can clear trichomoniasis and go on to carry a normal pregnancy later in the breeding season.
What’s tricky about trichomoniasis is that the disease may “fly under the radar” for a breeding season if only one or two infected bulls are present in the herd. Since bulls remain infected across breeding seasons, they can have a more profound and widespread effect on the herd earlier in subsequent seasons as they infect more cows, which in turn infect more bulls.
Detecting and Managing Trichomoniasis
Because trichomoniasis infections persist permanently in bulls (although they do not show outward signs of illness), detecting trichomoniasis as the source of reproductive problems is most efficiently done by testing bulls for the presence of the protozoa. Finding the germ in affected cows is less reliable, since they are only infected for a relatively short time compared to the bull.
The preferred diagnostic sample is obtained from scraping the inside of the bull’s sheath with a long pipette attached to a syringe for suction. (Vaginal mucus or a sample of pus from the uterus could be collected from suspect cows). The material is then submitted to a veterinary diagnostic laboratory (such as the Animal Disease Research and Diagnostic Laboratory at SDSU) for PCR testing. This sensitive test can detect a very small number of organisms in a sample.
Testing and removing affected bulls is essential for clearing an infected herd from trichomoniasis. There is no effective treatment for infected bulls, and the currently available vaccine does not prevent infection.
Keeping trichomoniasis out of herds in the first place is the focus of state regulations that require testing non-virgin bulls crossing state lines or changing ownership. In addition, South Dakota prohibits the sale of non-virgin open cows for breeding purposes in order to stop recently infected females from infecting new herds.
Because cattle do not show outward signs of illness specific to trichomoniasis, timely pregnancy diagnosis is a key to early detection of the infection in a herd. If an excessive number of open cows or abnormally spread-out pregnancies are detected, the herd veterinarian can help with advice on testing and herd management. General information on trichomoniasis can be found at the SDSU Extension website or in South Dakota, the Animal Industry Board website.
