Bovine Trichomoniasis: The Silent Disease
-Informational Bulletin Arizona Veterinary Diagnostic Laboratory
Trichomoniasis or “Trich” is a true venereal disease of cattle. It is caused by a single cell protozoan parasite, Tritrichomonas foetus and is characterized by early fetal death and infertility. It is found worldwide and is constantly present, or endemic, in the western and southwestern United States. In slaughter surveys approximately 8 percent of beef bulls are found to be infected. In some areas as many as 50% of the herds can be infected.
Tritrichomonas foetus is a species of protozoan that live in the skin lining the prepuce and distal penis of the bull and the vagina and uterus of the cow. It is pear-shaped with three small flagella (hairs) on the front and a single long flagellum on the rear. Trich cannot be observed without a microscope, but under low power they can be readily seen to move with a tumbling motion. T. foetus cannot form cysts so cannot survive out of the host animal for any length of time.
Transmission is direct from the infected bull to the cow during breeding. Once the T. foetus is deposited in the cow there is a rapid increase in numbers in the vaginal area. What occurs next is not clearly understood but the infection by T. foetus results in death of the embryo 15 to 80 days later. Cows and heifers typically return to heat one to three months after breeding but may remain infertile for two to six months after infection. In a few cases a cow may remain infected and deliver a healthy calf. These chronically infected cows can serve to infect bulls during the next breeding season. Most cows only carry T. foetus for a few heat cycles after infection and will clean up with sexual rest. Occasionally the infection will cause the cow to develop a pyometra or pus-filled uterus. When cows are actively infected, the T. foetus organism can be recovered from the lining of the vagina or from the mucous discharge.
Herd bulls are the long-term carrier of the infection. T. foetus finds a very good home in deep crypts and folds of the penis and fornix. Younger bulls are less likely to become permanent carriers, because they lack the deep folds found in older bulls. T. foetus is not found in semen but could be collected in an artificial vagina during semen collection if fluid from the prepuce is also collected. Because the infection in the bull is found in skin that is lining the penis there is no outward sign of infection. The only way to learn if a bull is infected is to collect fluid from the prepuce and try to grow T. foetus. The collection is done with a plastic infusion pipette attached to a 20-cc syringe. The pipette is inserted between the penis and the skin of the prepuce. The end of the pipette is rapidly moved back and forth while suction is applied using the syringe. This action breaks loose the skin cells and helps free up any T. foetus present. The collected fluid is transferred to a special liquid growth medium (InPouch TF) and observed daily for a week for the growth of T. foetus. A positive test is the observation of T. foetus in the medium under microscopic examination. There is no treatment for infected bulls and vaccination will not clear infected bulls or prevent infection of the bull.
Because this disease causes no outward indication of infection it may be in a herd for a long time before it is identified. Infection can cause devastating losses due to poor calf production and prolonged calving seasons. In newly infected herds pregnancy percentages may be reduced to 50-60 percent. A more subtle problem are chronically infected herds. Here the pregnancy percentage remains at a constant lower number (60-70 percent) and often environmental problems such as drought are blamed. The combined losses can result in as high as a 35 percent decline in economic return per cow in an infected herd. Total annual losses in the United States could exceed $500 million each year.
The first step in controlling Trich is to determine if your herd is infected. All bulls should be tested. To confirm the status of any individual bull three negative tests, each a week apart, are required. A single test on a single bull has only an 80 percent chance of finding an infected bull, so three tests are required to be 99 percent sure any single bull is clean. Any positive test shows an infected bull and you may assume you have an infected herd. The control of Trich in an infected herd can be difficult and costly and is dependent on herd size, breeding groups, breeding season and ability to control bulls. If you do have an infected herd, work with your animal health professional to develop a control program.
As with most health problems prevention is better than a cure. Use only virgin replacement bulls and do not purchase open mature cows. Year around breeding programs can make Trich hard to control and hard to identify. Replace old bulls with young virgin bulls to keep average bull age low. Examine a percentage or all cows for pregnancy status and monitor herd pregnancy percentages, this will tip you off if you develop a problem if there is an abrupt decrease in pregnant cows. A vaccine is available, but there are some limitations. It will not provide protection for the bulls, it requires an initial vaccination and a booster shot and does not prevent the cow from becoming infected but does allow her to clear her infection faster. Keep fences in good repair.
Other states have developed Trich control programs. Some are voluntary, such as California. Others have very tight controls and are trying to eradicate this disease from their state, such as Colorado. If you have further questions on this disease or on testing please contact me through the Arizona Veterinary Diagnostic Laboratory.