What group of adult cattle is most likely to be infected with the causative agent of bovine trichomoniasis?

The group of adult cattle most likely to be infected with the causative agent of bovine trichomoniasis is bulls older than 4 years of age. This is primarily because older bulls have been found to be more likely to carry and transmit Tritrichomonas foetus, the protozoan responsible for bovine trichomoniasis. These bulls can become carriers of the organism without showing clinical signs, leading to the spread of infection during mating.

In contrast, while heifers under 2 years of age and cows in their first lactation may be exposed to the parasite, they are less likely to act as reservoirs for the disease. Non-breeding bulls are also not typically involved in the transmission cycle since they do not participate in breeding and have limited exposure to the infective organism.

The high prevalence of infection in older bulls is a critical consideration when managing reproductive health in cattle herds, as it affects overall fertility and results in economic losses due to reproductive failures.