Comparative risk assessment for new cow-level Mycobacterium avium ssp. paratuberculosis infections between 3 dairy production types: Organic, conventional, and conventional-grazing systems

Abstract

Johne's disease, a granulomatous enteritis of ruminant animals, is a hidden threat on dairy farms, adversely affecting animal welfare as well as herd productivity. Control programs in the United States advocate for specific management practices to temper the spread of the causal organism (Mycobacterium avium ssp. paratuberculosis, MAP), such as improving calving area hygiene and limiting introduction of replacement stock with unknown infection status. A need remains for direct exploration of Johne's disease prevention strategies in the United States with respect to production type. Alongside the growing demand for organic products, the safety of organic dairy practices with respect to MAP control is warranted. Further, conventional herds for which organic practices such as pasture grazing are used should be situated within the risk spectrum. We developed a risk assessment model using the US Voluntary Bovine Johne's Disease Control Program as a framework, with the goal of evaluating the risk of new cow-level MAP infections. A total of 292 organic and conventional farms in 3 states were surveyed on management practices, and an overall analysis was conducted in which each farm was first scored on individual practices using a range of "no risk" to "high risk," according to the literature. The sum of all risk factors was then analyzed to quantify and compare the risk burden for each production type. Organic herds received higher overall risk scores compared with both conventional grazing and nongrazing subtypes. To identify which factors contributed to the overall increased risk for organic herds, the management practices were categorized and evaluated by logistic regression. We determined that the increased risk incurred by organic herds was predominantly due to decisions made in the calving area and preweaned calf group. However, although certain individual risk factors related to calf management are commonly involved in prevention strategies (e.g., cow/calf separation) and were thus included in the overall risk assessment, empirical evidence linking them to the spread of MAP is lacking. Instead, these factors are problematic when executed with other management decisions, leading to a hypothesized synergism of transmission risk. To this end, we developed a set of compound risk factors, which were also evaluated as outcomes in logistic regression models, with production type serving as the predictor of interest. Organic farms in our study were more susceptible to risks associated with the synergism of study variables. Notably, organic producers were most likely to allow calves to spend extended time with the dam, while also lacking a dedicated calving area. Additionally, calves in organic herds were more often permitted to nurse even with poor udder hygiene on farm. A heightened vigilance toward calving area hygiene is therefore indicated for these herds.

Longitudinal relationship between fecal culture, fecal quantitative PCR, and milk ELISA in Mycobacterium avium ssp. paratuberculosis-infected cows from low-prevalence dairy herds

“…The contamination of individual milk samples is of further importance in relation to the bulk tank milk supply; MAP bacteria have been implicated as a potential cause of Crohn's disease in humans (see Feller et al, 2007), with bulk tank milk as a conceivable vector. Further, both pasteurized and unpasteurized milk from the bulk tank is routinely fed to calves in 36 to 71% of US dairy farms (Beaver et al, 2016b), which could result in new infections given the heightened susceptibility of calves (Lombard, 2011). Over the course of our study, no bulk tank milk sample ever tested positive by PCR; furthermore, bulk milk ELISA OD values remained low and invariant.…”

Invited review: A systematic review of the effects of early separation on dairy cow and calf health

“…Of those herds that did use dedicated individual maternity pens, only 20 to 34% (depending on herd size) cleaned the area after each calving (USDA, 2016). There is evidence for a synergism of infection risk in the calving area, based upon the level of environmental cleanliness, udder hygiene, and presence of other lactating animals (Beaver et al, 2016). The evidence we have reviewed indicates that prompt calf removal should not be viewed as a substitute for proper hygiene and management in the maternity area.…”

Do Organic, Conventional, and Intensive Approaches in Livestock Farming Have an Impact on the Circulation of Infectious Agents? A Systematic Review, Focused on Dairy Cattle

“…IDs/IAs present on both CvsO and IvsE: five studies on MAP (Sn65-Sn67 CvsO [61][62][63] ; Sn10-Sn11 IvsE 64,65 ), four studies on viral infections (Sn71-Sn72 CvsO 66,67 , and Sn14-Sn15 IvsE 64,68 ), three studies on urogenital infections (Sn69-Sn70 CvsO 29,34 , and Sn13 IvsE 69 ), three studies on Campylobacter sp., (Sn60-Sn61 CvsO 70,71 , and Sn8 IvsE 72 ), four studies on ectoparasites (Sn62-Sn64 CvsO 49,24,25 , and Sn9 IvsE 73 ), two studies on zoonotic dermatophyte (Sn12 CvsO 74 , and Sn68 IvsE 74 ).…”