Consecutive Excretion of Mycobacterium avium Subspecies paratuberculosis in Semen of a Breeding Bull Compared to the Distribution in Feces, Tissue and Blood by IS900 and F57 Quantitative Real-Time PCR and Culture Examinations

Abstract

Paratuberculosis (Johne's disease) has emerged as one of the most important diseases in cattle. The role of infected bull semen in the spread of infection remains unclear as the correlation between the amount of excreted Mycobacterium avium subsp. paratuberculosis (semen and feces) and the infection load (blood and tissues) has not been defined. The aim of the present study was to study by culture, and a quantitative real-time polymerase chain reaction, the presence of bacteria in consecutive semen, blood, and fecal samples collected from one infected Piedmont breeding bull during a 380 day period. Five out of seven blood samples and all nine semen samples were positive on real-time quantitative polymerase chain reaction with 10¹ to 10² and 10² to 10⁴ copies of IS900/F57 per ml, respectively. In all, there were 9 fecal culture positive samples with too numerous to count colony forming units and positive real-time quantitiative polymerase chain reaction ranging from 10⁵ to 10⁷ copies of IS900/F57. After the bull was euthanized, Mycobacterium avium subsp. paratuberculosis was cultured from various parts of small and large intestines, liver tissue, lymph nodes, and from epididymis and vesicular glands. The results demonstrate wide extraintestinal distribution of the bacterium and awareness that breeding bulls should be considered as a source of paratuberculosis infection due to their contact with other breeding bulls and a high number of heifers and cows through the natural mating process.