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Introduction
Bovine trichomoniasis, or trichomonosis, is a sexually transmitted disease caused by the flagellate protozoan Tritrichomonas foetus. The infection is asymptomatic in bulls and linked to the development of a chronic condition, without affecting the quality of the semen or the libido [22] . In cows, T. foetus causes irregular heat cycles, early abortions, pyometra and temporary sub-fertility [23] . It is usually detected by extended breeding periods and lower pregnancy rates. The damages predicted through a model of the disease show a reduction of 14% in calf annual crop for a T. foetus prevalence of 20% in a herd [25] .
Although trichomonosis is worldwide distributed, the incidence of the disease has decreased or even has been eradicated from some regions where artificial insemination is widely practiced. However, in countries with extensive farming systems, the artificial insemination is not a realistic choice. These countries have implemented annual reports with the intention to control the affection [19] . The practiced systematic approach of bovine trichomonosis control relies upon identification of infected bulls followed by their removal from the herd. The infection is recognized by microscopic test of cultures inoculated with preputial samples. The presence of T. foetus can be confirmed through polymerase chain reaction (PCR) followed by agarose gel migration, by quantitative PCR or by loop mediated isothermal amplification (LAMP) [14,21,17,20] . Several states in USA, Australia and Argentina have enforced rules and restrictions to curtail the disease. Testing and culling is an effective practice to control the prevalence of the trichomonosis; however, to increase the system efficiency, new management procedures would be desirable [27,6] .
The commercially available vaccines in Argentina (Tricovac) and USA (TrichGuard®) are based on killed T. foetus cells combined with proprietary adjuvants. Experimental vaccines based on killed T. foetus cells have shown to reduce the number of infected cows by shortening the period of genital infection and by increasing the percentage of pregnancy in comparison to non-vaccinated animals [16,2,10] . Other preparations containing fractions of T. foetus cells such as membranes or glycoproteins were also able to increase the antibody levels and reduce the time of infection in cows [3,1,9] . To our knowledge these vaccines were not shown to prevent the colonization of the genital tract.
The adjuvants enhance...