Invited Review: Management of trichomoniasis in cattle production

Invited Review: Management of trichomoniasis in cattle production

Brenyn N. Burkholder

Department of Animal Science, Texas A&M UniversityÂ

INTRODUCTION

Trichomoniasis in cattle is a sexually-transmitted disease caused by Tritrichomonas foetus, a parasitic flagellated protozoan (Collantes-Fernández et al., 2014). Tritrichomonas foetus effects cattle by attaching to the epithelial surface of the penis of bulls (Jin et al., 2014). Once the parasite takes a bull as its host, the bull is permanently infected with trichomoniasis but remains an asymptomatic carrier (Mardones et al., 2008). The infection is transmitted to cows and heifers through natural service and attacks their reproductive system (Collantes-Fernández et al., 2014). Bovine trichomoniasis causes reproductive failure in cows and in heifers which can result in abortion, infertility, vaginitis, or early embryonic death (Molina et al., 2018). There is no treatment to eradicate Tritrichomonas foetus once a bull is established as a host, so the most common solution is to cull infected bulls (Alling et al., 2018). In cows and in heifers, the infection is often cleared within a few months from partial immunity, while females which do not clear the infection, can be cured through various treatment methods (Yao et al., 2013). Trichomoniasis has an estimated economic impact of 650 million dollars on the U.S. cattle industry from expenses such as treatment costs and money invested in infected bulls which will be culled (Molina et al., 2018).

RISK FACTORS

As previously addressed, Bovine trichomoniasis is spread throughout a herd by natural service. Cows or heifers are infected immediately at the time of mating, and surprisingly fertilization can still occur in an infected female (BonDur et al., 1997). However, pregnant infected females typically lose the developing fetus at about 14 to 18 days after fertilization (BonDur et al., 1997). Trichomoniasis has become a large problem in the cattle industry because the spread of infection is often not discovered until it is too late (Bhattacharyya et al., 1997). In addition, since bulls are typically asymptomatic carriers of the infection and show no outward signs, infection is generally noticed when infertility or abortion is present in cows or heifers (Yao et al., 2013).Â

To stop the spread of trichomoniasis throughout a herd, infected cattle must be tested and culled, otherwise the whole herd stays at risk (Islam et al., 2017). There are multiple methods to collect samples from a bull for testing, but scraping inside the penis shaft is the most widely used collection method in the United States (Yao et al., 2013). In addition, there are multiple forms of testing and diagnosing the infection; including culture testing, PCR testing in real-time, and gel electrophoresis measurement of PCR (Yao et al., 2013). These different methods of testing vary from state to state depending on the environment the cattle are raised. A study conducted at the University of Wyoming proved that PCR tests are more sensitive and produce less false-negative results in comparison to culture tests (Yao et al., 2013). Â

A main problem in effectively removing infected cattle from the herd is identifying them in the first place (Molina et al., 2018). Undetected carrier cows are mainly responsible for the spread of trichomoniasis throughout a herd since the infection could be transferred to all other cattle without any initial signs (Molina et al., 2018). A study conducted at the National University of La Palma proved that the most effective way to stop the spread of trichomoniasis from cows to bulls is to cease sexual contact for six to nine months so that the infection in cows can naturally clear (Molina et al., 2018).Â

Sharing bulls or selling them to another producer is also a high-risk factor. A study conducted at the Center for Animal Disease Modeling and Surveillance showed that sharing cattle increased the rate of bulls testing positive for trichomoniasis by 5.4 times (Mardones et al., 2008). Furthermore, introducing replacement heifers into a herd can further permit the spread of the disease (Collantes-Fernández et al., 2014). Thus, the best way to ensure that an infected heifer or bull is not introduced to the herd is to only purchase virgin cattle (Mardones et al., 2008). Another less effective method is to administer a trichomoniasis test to cattle which will be traded or purchased (Jin et al., 2014). The main issue with this method of prevention is the chance of receiving a false-negative test (Molina et al., 2018). There are several factors which influence the accuracy of bovine trichomoniasis tests including the process for sample-collection, the sampling interval, and the type of storage the test is contained in (Molina et al., 2018). The safest method to ensure the highest level of accuracy is to test cattle two to four times before officially clearing them free of the infection (Molina et al., 2018).Â

Another risk factor involves the number of bulls present in a herd and the age of bulls. A study conducted at the University of Florida provided evidence that herds with greater amounts of bulls have a higher chance of having at least one animal test positive (Molina et al., 2018). In addition, a study conducted by the CSIRO Division of Animal Health at the Animal Health Research Laboratory concluded younger bulls at one to two years of age are relatively insusceptible to Tritrichomonas foetus (Clark et al., 1974). Â

BREEDING METHODS

Bovine trichomoniasis is most commonly spread in countries that rely on natural service as the main form of breeding; such as Asia, South America, and South Africa (Yao et al., 2013). As previously stated, it is difficult to identify the presence of Tritrichomonas foetus in herd quick enough to prevent the spread of the infection. Therefore, in these countries, the infection can quickly spread throughout the cattle trade without proper testing. On the other hand, European countries and the United States rely on artificial insemination for breeding opposed to traditional natural- service (Yao et al., 2013). Artificial insemination has caused a substantial reduction in the spread of Bovine trichomoniasis (Mardones et al., 2008). Tritrichomonas foetus is able to survive in harsh conditions such as the freezing of semen following collection, but it is not able to withstand the high temperatures needed to heat the semen before it is deposited into a female (Islam et al., 2017). Therefore, artificial insemination is an effective method to stop the spread of the infection during breeding season.

The foreign countries previously stated will continue to have Bovine trichomoniasis spread throughout their herds until infected bulls are culled and artificial insemination becomes a common method of breeding. In addition, keeping cows and bulls separated during breeding seasons is crucial to ensure that an artificial insemination program is effective to prevent the spread of the infection (Collantes-Fernández et al., 2014).Â

TREATMENT AND PREVENTION

Currently there are no effective methods to treat bulls infected with Tritrichomonas foetus. A study conducted at the University of Florida tested the use of therapeutic vaccination of bulls to prevent the infection, but results suggested that there was no practical benefit of the vaccination as it did not prevent Tritrichomonas foetus from infecting the bulls (Alling et al., 2018). In the past, substituted imidazoles helped treat Tritrichomonas foetus, but shortly after they were introduced, they were deemed unsafe and are now illegal (BonDur et al., 1997). In the absence of an effective vaccination for bulls, cattle producers must rely on the previously stated preventive measures (Figure 1). In terms of treatment in females, cows and heifers can be vaccinated against Tritrichomonas foetus using initial immunizations prior to breeding (BonDur et al., 1997). The vaccination, TrichGuard V5-L HB made by Boehringer Ingelheim is commonly used to prevent the spread of the infection (BonDur et al., 1997). This vaccine needs to be administered twice prior to breeding with at least one month separating each injection (BonDur et al., 1997). Therefore, females are apparently easier to manage in the presence of Bovine trichomoniasis.

CONCLUSION

Bovine trichomoniasis has a significant impact on the cattle industry by decreasing reproductive efficiency in beef herds. The parasite Tritrichomonas foetus which causes the infection of Bovine Trichomoniasis, causes heavy economic losses including the costs of testing and culling bulls, along with missed cash-flow from cows unable to produce offspring. In the United States, cases of Bovine Trichomoniasis are relatively low due to the wide acceptance of artificial insemination. For producers using natural service as a method of breeding, testing bulls should be a routine practice to ensure the prevent transmission of the parasite and infection. Ultimately, eradicating trichomoniasis in an infected herd is managed by culling infected bulls and separating infected cows or heifers. Since there has yet to be an effective vaccine approved for the market, further studies should be conducted to ultimately produce an effective vaccination for producers to use. In addition, further studies should also be conducted on how to save pregnancies of cows or heifers that are infected at the time of fertilization.

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