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Understanding consequences of Trich and new rules for disease

published: October 2nd 2009
by: Martha Hollida Garrett

Bull buying season is here and with it comes new rules concerning Tri-chomoniasis (Trich) for bulls purchased out-of-state, effective April 2009 and another new set of regulations for bulls purchased in-state, beginning January 1, 2010.
    Trich is a costly disease as it directly affects the number one economic trait in the beef business—reproduction.  A Trich infected herd results in early pregnancy losses, late abortions, extended calving season, mild to severe pyometria (swollen uterus with infection in some but not all infected cows and large, firm reproductive tracts in some cases, as the result of metritis and scarring of the uterus.
    The disease has been more prevalent in western states, but now it is showing up in herds across the Midwest and Texas, so the Texas Animal Health Commission (TAHC) has issued new rules to minimize the losses in Texas herds. A number of other states have also issued new rules and regulations. These two sets of rules are posted at the conclusion of this article. In addition, producers are urged to check with any state they may be purchasing bulls from or shipping bulls to concerning Trich requirements (see page 7).            Trich is a venereal disease that has no visible symptoms in the bull and few if any in heifers and cows. It is caused by the protozoan, Tritrichomonas foetus. Trich prefers a reduced oxygen environment. It lives in the crypts on the muscuosal surface of the penis and prepuce of the bull.
    Cows become infected when the protozoa enters through insemination. It infects the lining of the uterus, vagina, oviducts and cervix, making it possible for cows to transmit the disease to other bulls if inseminated by more than one bull. It causes an inflammatory response in the uterus of the cow for approximately 42 to 56 days after insemination by the infected bull. It is believed that this time frame accounts for the high incidence of abortions starting at six to eight weeks after conception in newly infected animals. The infection process is not a random event, as 80 to 90 percent of cows bred to an infected bull will acquire the disease.
    An extended period of sexual rest (120 to 150 days) will allow most cows to rid themselves of the infection. However, this immunity is short-lived and a cow can become reinfected.
“This is a not a disease that can be treated. Bulls must be sent to slaughter if they have it. Cows will clean themselves over a period of time, which usually is 4-6 months. There is work ongoing to see if the disease is chronic in cows. If cows continue to show up open, I encourage producers to also send these to slaughter, unless for example they are in a purebred herd and there is tremendous genetic material represented,” says Dr. Gary Warner, with Elgin Veterinary Clinic, Elgin, Texas.
    According to Dr. Tom Hargrove with Texas A&M AgriLife Extension, cows exposed to Trich cannot be considered safe in calf until they are last 120 days pregnant and open cows cannot be considered to non-infected until at least 90 days of sexual rest and examination by a veterinarian. Approximately 2% of the infected cows will maintain a swollen uterus containing pus and remain infective and open cows with pyometria should be sent to slaughter.
    Trich should be suspected in herds with poor conception rates and extended calving season. Conception rates can vary from slightly subnormal to 50% or lower depending on the length of time the disease is in the herd and the number of animals that are infected. More dramatic presentations will be seen in herds with controlled breeding season of 90 days or less. However, shorter breeding season will lead to earlier detection of a problem and can reduce the long-term effects and costs associated with herd infection.
    Dr. Warner says the number one thing to do if you think you have Trich is palpate and find out how many open cows you have and test your bulls. These can be tested either through a series of three culture tests or through the RC-PCR test (Real Time-Polymerase Chain Reaction). A bull thought to possibly be a carrier must have three tests each a week apart and pass each test to be considered clean.
    Infected bulls must be sold for slaughter and remaining bulls in the herd must be held and isolated from female cattle until the females are clean.
    Cows can be vaccinated to help reduce the severity of the disease, but the infection can only be transmitted by sexual intercourse and not by the environment.
    The best way to prevent Trich is to prevent exposure. The protozoa enters the herd or ranch only via infected bulls, cows or heifers. Also please note that it is not transmitted to people.
    Hargrove outlines the following biosecurity practices that should be adhered to concerning Trich.
1. Maintain good perimeter fences, thereby controlling movement and commingling of cattle of unknown status.
2. Purchase only virgin bulls and heifers, preferably from the original breeder. Unless virgin status of bulls can be positively confirmed, test all bulls prior to adding to herd. All bulls of unknown status should have three negative tests using PCR or culture. These tests should be administered at least one week apart and the bull should have no contact with cows within one week of the initial test.
3. Keep the bull battery as young as possible.
4. Consider artificial insemination as a tool to avoid introduction of Trich or to help break the cycle of infection in a herd. Reputable semen companies repeatedly test bulls for numerous diseases including Trich to ensure semen is not contaminated.
5. Implement a defined breeding season. Trich may go undetected in continuous breeding herds.
6.  Identify herd sires and record breeding groups each bull is exposed to. If a problem is detected, it is easier to isolate the problem and initiate management protocols to eliminate the disease.
7. Consider keeping bulls in the same breeding groups for several breeding seasons. Should there be a false negative bull in the battery; this practice prevents exposure of native cattle.
8.  Consider small sire groups (but not necessarily single sire), versus large multiple sire herds to avoid infecting a large number of bulls in a single season. One-herd grazing systems should closely monitor pregnancy and implement an annual bull-testing program to detect introduction of Trich during the first breeding season.
9.     Avoid purchasing open or short bred (less than 120 days) cows and      never add cows that are open or bred less than 120 days to a herd without appropriate examination and quarantine if you do not know the status of herd of origin. Purchas-ing young open cows from unknown sources is particularly risky.
10. If replacements are purchased, do not commingle with the existing herd during the first breeding season.