Dairy farms testing positive for Mycobacterium avium ssp. paratuberculosis have poorer hygiene practices and are less cautious when purchasing cattle than test-negative herds.

Discipline: disease; Key words: paratuberculosis, Mycobacterium avium ssp. paratuberculosis, risk factor, cattle, environmental samples

Mycobacterium avium ssp. paratuberculosis (MAP), the causative agent of Johne’s disease, is present on many dairy farms over the world, also in South Africa. It is causing significant economic losses and its presence presents a potential public health concern. A study to identify and understand the risk associated with MAP would therefore be valuable. This was the objective of an Alberta study by Dr R Wolf and colleagues, which was published in the Journal of Dairy Science, Volume 99 of 2016, pages 4526 to 4536, the title being: Dairy farms testing positive for Mycobacterium avium ssp. paratuberculosis have poorer hygiene practices and are less cautious when purchasing cattle than test-negative herds.

Risk assessments were conducted and environmental (potential contamination points) samples were collected on 354 Alberta dairy farms that voluntarily participated in the Alberta Johne’s Disease Initiative. Using the statistical technique of univariate logistic regression, risk factors addressing animal and pen hygiene, as well as the use of feeding equipment to remove manure and manure application on pastures, were associated with the number of positive environmental samples. Based on factor analysis, risk factors were clustered and could be summarized as four independent factors: (1) animal, pen and feeder contamination; (2) shared equipment and pasture contamination; (3) calf diet; and (4) cattle purchase. Using these factor scores as independent variables in multivariate logistic regression models, a one unit increase in animal, pen and feeder contamination resulted in 30% higher odds of having at least one positive environmental sample. The same result applied for cattle purchased. Furthermore, a 100-cow increase in herd size resulted in an odds ratio of 110% for having at least one positive environmental sample.

It was concluded that cleanliness of animals, pens and feeders, as well as cattle purchase practices, will substantially affect the risk of herd infection with MAP. Therefore, improvements in those management practices should be a focus in controlling MAP. No doubt, these results have implications on control of other diseases as well. Careless purchases and indifferent bio-security are main reasons for the spread of diseases such as Bovine Brucellosis.