Lessons leaned from the Michigan Johne's Disease Control Demonstration Project (Proceedings)

The Michigan Johne's Disease Control Demonstration Project is a cooperative program between Michigan State University (MSU), Michigan Department of Agriculture (MDA), and the United States Department of Agriculture (USDA). It is part of a larger disease control demonstration project being conducted in 16 other states. The objective is to demonstrate and investigate management factors that are effective in controlling Johne's Disease (JD). Eight dairy farms and one beef farm are enrolled in the project. Herds represent a variety of housing and management systems. A JD control program was developed for each individual herd. The prevalence of JD in the respective herds is tracked annually through repeated testing. Each herd's control program is reviewed annually and updated as necessary. In addition, several field based research projects are being conducted to develop new knowledge on the control of JD. Below is a summary of some of some of the findings from this project.

Isolation of Mycobacterium Avium Subsp. Paratuberculosis From Recycled Sand

Johne's disease (JD), caused by the bacterium Mycobacterium avium subsp. paratuberculosis (MAP), is a chronic untreatable disease of ruminants. It primarily affects the intestinal tract resulting in chronic diarrhea and weight loss. JD is transmitted to young stock through the ingestion of colostrum, milk or feedstuffs contaminated with MAP or through exposure to MAP contaminated environments. Many dairy farms use sand as a bedding material and new technology has been developed to recycle sand and reuse it. In some instances, recycled sand may be used for bedding of replacement heifers that are most susceptible to infection with MAP. This study was conducted to determine if MAP could be found in recycled sand, thus serving as a source of environmental exposure to susceptible animals.

Two dairy farms known to be infected with MAP were used in this study. One farm was visited weekly for 4 weeks during the summer and for 3 weeks during the winter of 2006/2007 (n=7 visits). The other farm was visited once every 6 months from 2004-2006 (n=6 visits). On each farm, a 4 oz sample was collected from the pre sand separation holding area, the post separation recycled sand pile and the post separation organic material holding area (lagoon). Samples were submitted to the Michigan State University Diagnostic Center for Population and Animal Health where they were cultured for MAP using a liquid culture system (TREK ESP II, TREK Diagnostic Systems, Cleveland OH). Positive samples, as determined by the TREK liquid culture system were confirmed by both acid-fast staining and IS900 PCR.

MAP was cultured from 12/13 samples collected from the pre separation holding tanks. Post separation, MAP was cultured from 11/13 and 13/13 of the post separation sand pile and post separation organic material respectively. There was no difference in the frequency of MAP recovery based on farm or season of the year.

This study demonstrates that on infected dairy farms, MAP can be found in recycled sand and can potentially serve as a source of disease exposure if used as bedding for susceptible animals. Veterinarians should recognize this risk when conducting Johne's disease risk assessments and advise their clients on how best to manage recycled sand to reduce risk of MAP transmission. Future studies will attempt to determine how long MAP may remain viable in recycled sand and to identify management strategies to reduce survivability.

Environmental Distribution of Mycobacterium avium supsp. Paratuberculosis On Michigan Dairy Farms

Johne's Disease (JD) is an important infectious disease of cattle caused by Mycobacterium avium subspecies paratuberculosis (MAP). It is estimated that over 50% of US dairy herds are infected with MAP. Environmental contamination with MAP is considered the major reservoir of infection for susceptible cattle. While MAP does not multiply in the environment, it can persist for months in manure, lagoons, manure packs—areas that are found in abundance on most dairy farms—even in below-freezing temperatures. Very little information is published of the distribution of MAP on dairy farms. The objectives of this study were to: 1) perform serial environmental culturing on six Michigan dairy herds, enrolled in a JD control program over several years; 2) characterize the distribution of MAP contamination on dairy farms; and 3) determine if and how that distribution changes as herd fecal culture prevalence changes.

The dairy herds sampled in this project are participants in the ongoing Michigan Johne's Disease Control Demonstration Project and vary in size from 80 to 400 cows milking. Feces from all adult cows were cultured annually for MAP, and herd fecal culture prevalence calculated. Additionally, every six months, composite samples of feed, water, and flooring were collected and cultured for MAP from each of four animal housing areas on the farm: calf, transition heifer, maternity, and lactating cow. Samples were also collected and cultured from the primary manure collection area (lagoon or manure spreader), recycled sand bedding, and pasture areas where applicable.

A total of 454 environmental samples were collected for MAP culture from the six herds from 2003 through 2005. MAP was cultured from 45 (10%) environmental samples. The manure collection area was most commonly culture positive for MAP, 13 (3%); followed by lactating cow floor, 12 (2.6%); maternity floor, 5 (1%); maternity water, 4 (0.8%); calf floor, 4 (0.8%); recycled sand bedding, 2 (0.4%); and calf feed, 2 (0.4%). One sample each from lactating cow feed, lactating cow water, and heifer floor was positive for MAP. Fecal culture prevalence of the herds during this time ranged from zero to 42%.

There was a tendency for herds with higher MAP fecal culture prevalence to have more MAP positive environmental samples. As fecal culture prevalence declined, the number of MAP positive environmental samples also declined. Also, positive environmental samples tended to go from being classified as moderate or heavy shedders, to low or very low shedders as herd fecal culture prevalence decreased.

MAP was consistently found (92% of the time) in the manure collection area and/or lactating cow floor when herds had fecal culture prevalence greater than two percent. Once herds reached a prevalence of less than two percent, MAP was never cultured from any area sampled. Conversely, once herds exceeded a fecal culture prevalence of five percent, MAP contamination was found in areas other than the manure collection area and lactating cow floor, most commonly the maternity floor.

On the farms in this study, MAP was most commonly cultured from the primary manure collection area and lactating cow floor. These are the areas on the farm where there is the greatest concentration of manure from the greatest number of mature cows, who are at greatest risk of shedding the bacteria. The number of MAP culture positive environmental samples, and the classification of shedding in those samples, tended to increase as the number of cows shedding MAP in the herd increased. The incidence of environmental contamination with MAP was highest in the primary manure collection area followed by the lactating cow area and the maternity area. The fact it was not uncommon for MAP to be isolated from the maternity area, particularly the floor, is concerning because calves, the animals most susceptible to MAP infection, are being born in these areas. This implies cleanliness and sanitation of the maternity pen must be emphasized when trying to control JD.

Finally, MAP was cultured 92% of the time from the primary manure collection area and/or lactating cow floor in herds with greater than two percent MAP fecal culture prevalence. This suggests "targeted" environmental sampling could be used to screen dairy herds for JD. Targeted environmental sampling may provide a reliable and cost effective tool for producers to monitor the progress of their JD control program.

Detection of Mycobacterium Avium Subsp. Paratuberculosis on the Exterior of Periparturient Cows: Implications For Vertical Transmission

It has been recently demonstrated that the presence of Mycobacterium avium subsp. Paratuberculosis (Para Tb) in the environment can be, through the use of targeted sampling techniques, a good predictor of the presence of Johne's disease in a dairy herd. Our study attempted to illustrate how environmental contamination, with Para Tb organism, may increase the risk of transfer of the bacteria from dam to offspring, independent of the shedding status of the dam.

The sampling frame was a 140 cow dairy herd, enrolled in Michigan's Johnes demonstration project, with a decreasing test prevalence of Johne's disease (3% 2005 compared to18% in 2002). We selected 7 cows for sampling. Six were due to calve in less than 3 weeks and were the only animals housed in an area adjacent to the maternity pen. The seventh cow had vacated that area just prior and calved on test day. With each of the seven cows we swabbed three areas that are prone to be nuzzled in "teat seeking" by the newborn calf (base of teat, hock, and area posterior to Olecranon) with gauze 2x2's dampened with sterile water. The 21 samples were prepared using the Cornell method and cultured in the liquid culture TREK system at Michigan State University. Positive cultures were confirmed with both PCR and Acid Fast Staining.

Five of the six cows (83%), housed in the area next to maternity pen, had at least one positive sample site and two of six (33%) had multiple sites culture positive for Para Tb. Interestingly, none of these six cows were fecal or ELISA positive themselves, and were tested for this concurrently during the annual "whole herd" test. To determine the origins of this contamination we looked at the location of the four fecal shedders in herd at the time of the testing. One was the seventh cow we tested and had just left the area three days prior (she was positive on all three sites) and two of the other three fecal shedding cows had just vacated the area of concern two weeks prior to testing.

Conclusion: It is documented that most animals with Johne's disease are infected as a neonates. Five of the six cows tested had external bacterial contamination even though testing negative for fecal shedding, leading one to surmise that the presence of this organism on these five animals presented a huge risk to their offspring even in a herd with declining prevalence. This study provides impetus to remove calf quickly from dam and to mitigate environmental contamination.

Longitudinal Study of Risk Factors Associated with Cows being Fecal Culture Positive for Mycobacterium Avium Ssp. Paratuberculosis on Michigan Dairy Farms.

Johne's disease (JD) is a chronic disease prevalent on many dairy farms. Cattle generally become infected with the causative agent, Mycobacterium avium ssp. paratuberculosis (MAP) as young calves, but do not develop signs of the disease for 2-5 years. Control of JD has focused on implementing management practices to prevent calves from becoming infected based on knowledge of JD pathogenesis. Due to the chronic nature of JD and the management dynamics on most dairy farms, it has been difficult to prioritize which practices are most effective in preventing JD. The objective of this study was to determine which risk factors are associated with MAP infection in dairy cows over time.

Six Michigan dairy herds infected with JD participated in this longitudinal study as part of the NAHMS Johne's Control Demonstration Project. Serum ELISA and fecal culture for MAP using either standard culture on HEY or the ESP® Culture System II was performed on all adult cows annually. A standardized JD risk assessment was also performed annually, providing scores for perceived risk of MAP infection based on management in five areas on the farm—maternity, pre-weaned calf, weaned calf, bred heifer, and lactating cow. Individual cows within herds were assigned the risk scores for each area consistent with when they were present in that area. These risk scores, along with lactation number and ELISA score, were used as the independent variables in a logistic regression model with fecal culture result (positive/negative) as the outcome. Due to the longitudinal nature of the study, repeated measures within cows and clustering of cows within herds was controlled using GEE with an exchangeable correlation structure. On these farms, after controlling for age and ELISA score, maternity pen cleanliness at birth was the primary factor associated with cows being MAP culture positive as adults.

Prevalence of Dairy Herds Infected with Johne's Disease in Michigan as Determined by Environmental Sampling

Johne's disease (JD) costs the US dairy industry an estimated $200-250 million annually due primarily to reduced production and cull value of infected cows and increased replacement costs. Due to the significant effects on herd productivity, along with the potential public health consequences should MAP be linked to Crohn's Disease in humans, voluntary JD control programs have been implemented at the both the national and state levels. Substantial resources have been committed to these control programs, but their success has been difficult to ascertain due to the lack of an efficient monitoring program. The objective of this study was to estimate the prevalence of Grade A dairy herds infected with JD in Michigan using a novel environmental screening protocol.

Ninety-four randomly selected dairy herds were surveyed for JD by culturing environmental samples for Mycobacterium avium ssp. paratuberculosis (MAP) using the ESP® Culture System II. One sample each was cultured from the primary manure storage area and a high-traffic common cow area. A herd was classified as infected with JD if at least one sample cultured positive for MAP. State, agricultural district, and herd size stratum prevalence was calculated. Information on past JD testing and cattle purchase history was collected, and logistic regression was performed to determine their importance to the JD status of the herd. Thirty-eight (40.4%) of 94 herds were positive for JD, including all herds (n=15) with greater than 200 lactating cows. Herds that had tested for JD or purchased cattle in the previous five years were 4.6 and 3.1 times, respectively, more likely to be infected than herds that had not. Johne's disease continues to be prevalent on Michigan dairy farms. The environmental sampling protocol used in this study is an economically attractive alternative for monitoring the progress of JD control programs at the state or national level, as well as the individual herd level, and could help guide changes to control programs over time.

Cost of Johne's Disease Control Programs on Michigan Dairy Farms

The NAHMS Dairy 1996 study estimated that 22% of US dairy herds are infected with Johne's Disease (JD), but other estimates range from 21-93% depending on region and testing method used to identify infected herds. In a recent stratified random survey of dairy farms in Michigan, it was estimated that up to 49% of the state's dairy herds were infected with JD. Anecdotal reports by private practitioners in Michigan suggest this estimate is extremely conservative. Regardless of the estimate, JD is a prevalent disease on many dairy herds resulting in economic losses due mainly to lost production, increased culling, decreased cull value, and increased replacement costs. The literature estimates annual losses due to JD in US dairy herds range from $22-26 per cow across all cattle in an infected herd. Johne's Control programs are commonly recommended, but very little information is available on the cost to implement these programs. The objective of this study was to quantify the costs of JD control programs implemented on dairy herds over time and determine their impact on herd prevalence.

An economic questionnaire was administered to six Michigan dairy herds enrolled in a JD control program annually (2004-2006) to assess costs directly attributable to the control program. The questionnaire consisted of four categories: supplies/testing, management, labor, and capital investment. Costs for each category were calculated and adjusted to 2006 US dollars. Concurrently, JD prevalence on these herds was monitored by annual whole herd fecal culture or serum ELISA testing.

The cost of JD programs on these farms ranged from $24-109 per cow per year with a mean of $63 per cow per year and a median of $58 per cow per year. The majority of the costs fell in the testing and supplies category, followed by labor costs, with costs for management and capital investments being fairly equal when averaged across all herds. Over the same period JD prevalence, as measured by whole herd fecal culture and/or serum ELISA, within these herds dropped 3-30%. There was a trend across these herds for a reduction in the percent of first lactation cows being fecal culture positive (an indication that practices put in place to prevent new JD infections are working). However, there was no apparent association between the amount spent on a control program and the magnitude of decrease in apparent within herd JD prevalence.

This study provides a rough insight into how much dairy farms are investing into JD control programs. Results also suggest that money spent on a JD control program does reduce within herd prevalence, but a more thorough benefit-cost analysis is needed to determine if JD control programs are cost effective.

Using ELISA Adjusted Optical Density (OD) Measures to Predict Mycobacteria avium supsp. paratuberculosis Shedding Status of Individual Dairy Cattle

Fecal culture remains the standard for diagnosing Mycobateria avium paratuberculosis (MAP) in individual cattle, however it generally requires 8-16 weeks to obtain results. The enzyme-linked immunosorbent assay (ELISA) has a rapid turn-around time, although its sensitivity is poor, especially in subclinically infected cattle. It is generally accepted that as the infection progresses mean ELISA response and sensitivity increases. Cattle infected with MAP have a long prepatent period in which no shedding of the organism occurs followed by intermittent then continuous shedding increasing in volume as disease progresses. While any cow infected with MAP is undesirable, only cattle shedding the organism pose an immediate threat to other cattle. These cattle generally have higher ELISA optical density (OD) values compared to cattle not shedding MAP. The objective of this study was to compare the ELISA adjusted OD values of cattle with negative fecal cultures to cattle classified as either low (≤10 cfus) or high (>10 cfus) shedders and determine the positive likelihood ratios for each.

Fecal culture results and ELISA OD values were evaluated from 2,578 adult cattle from six Michigan dairy herds over two years. Based on fecal culture results cattle were classified as fecal culture negative, low shedders (≤ 10 cfu's), or high shedders (>10 cfu's). The mean adjusted ELISA OD and accompanying 95% CI were calculated for each group. Using the mean as the ELISA cutoff for each respective group and comparing it to fecal culture results, two by two tables were constructed and positive likelihood ratios calculated.

Prevalence of MAP in these herds based on fecal culture ranged from zero to 42% with an average of 9.8%. The mean ELISA OD value for fecal culture negative cattle (n=2,362) was 0.023 (95% CI: 0.02-0.03). That for cattle classified as low shedders (n=158) and high shedders (n=58) was 0.201 (95% CI: 0.12-0.28) and 0.784 (95% CI: 0.52-1.05), respectively. The likelihood ratios of a positive test for fecal culture negative, low, and high shedders were 3.2, 9.7, and 21.9, respectively.

Given the ELISA OD, the likelihood ratios can be used to predict the probability of a cow shedding MAP, provided herd prevalence information is available. This information is valuable in aiding producers making individual cow management and culling decisions.