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Mycobacterium avium subsp. paratuberculosis (Map) is the causative agent of a chronic granulomatous enteritis known as paratuberculosis, one of the most important diseases for cattle and the livestock industry worldwide, due to its considerable economic impact triggered by progressive and fatal weight loss of the animals, reduction of productivity, infertility and decreased milk production. The major routes of infection in ruminants are intrauterine and fecal-oral, through contact with fecal material from an infected animal and/or ingestion of contaminated colostrum and milk (Windsor & Whittington, 2009). Transmission of Map usually occurs during the first months of life, with calves under 6 months of age being the most susceptible to infection due to their immature immune systems, meaning an infective dose of about 50-103CFU per calf (Windsor & Whittington, 2009).
Dairy farmers often feed calves with waste milk (Duse et al. 2015), a mixture of excess colostrum, transition milk and non-saleable milk from cows that have been or are still being treated with antibiotics. Feeding calves with waste milk may represent an economic benefit for farmers not only because it leads to savings in milk replacer, but also because feeding whole milk has been shown to lead to higher growth rates than feeding milk replacer with the same gross composition (Lee et al. 2009). This practice may, however, present a risk for calves due to the potential development of antimicrobial resistant faecal flora (Duse et al. 2015) and infection with pathogens, including Map that leads to the spread of paratuberculosis (Ridge et al. 2005).
The diagnosis of paratuberculosis is difficult and time consuming, due to the characteristics of the agent, and is influenced by the stage of the disease. Faecal culture is considered the gold standard method for Map diagnosis, but it may take up to 6 months for growth of the mycobacteria. The introduction of molecular diagnostic techniques has contributed to a faster and more sensitive detection of Map from biological samples including tissues, faeces and milk. Real time PCR is increasingly used for the direct detection of Map from biological samples due to its higher sensitivity and faster analysis time than conventional PCR and culture.
The present work aimed at evaluating...