Adopting a New Culling Strategy to Reduce Johne’s Disease and Improve Economic Sustainability on Dairy Farms

Survey Results 

Nine farms completed the survey. Respondents were comprised of 33% certified small farm operations (51-199 milking animals), 44% medium farm operations (200-699 milking animals), and 22% large farm operations (milking greater than 700 animals).  

Figure 1: Partner farms represented by number of milking cows.

Responses to the question ‘What is your level of concern regarding Johne’s disease on your farm?’ ranged from a little to moderate. Four of the nine herds had previously participated in a nationally funded program called VTCHIP that provided testing and veterinary services to help farms reduce Johne’s disease, so many of the participating farms had knowledge of Johne’s disease and diagnostic testing. Concerns related to the economic impact of Johne’s disease on the farm ranged from not at all concerned to extremely concerned. More than half of the respondents did not know whether Johne’s disease was present on their farm, or they were not culling cows exhibiting clinical signs which led to less concern about the economic impacts of the disease. Two participants had previous experience with the negative economic impacts of Johne’s disease in their herds, and had personal experience with how devastating the disease can be. All farms were implementing some type of Johne’s disease control methods, even if they did not initially recognize management practices as such. All respondents indicated that livestock health was very important when making management decisions. Economic impact when making management decisions was ranked as very important by 78% of participants, with the remaining 22% ranking it as somewhat important. 

When asked about details for culling animals, primary reasons included feet and legs, reproductive status, low production, and somatic cell count. Responses to the question of how likely they would be to implement a culling strategy to help reduce Johne’s disease on farm were varied, but participants would be more likely to cull animals that had a positive test result. This response was further supported by a follow up question that asked participants to select the practices they thought were acceptable for managing Johne’s disease on their farm. 67% of participants would cull if individual test results suggested they do so, while 11% would cull if economic impacts suggested they do so, and 22% would cull if test results, production records, and economic impact suggested they do so.  

Environmental Results 

Results from the environmental samples taken from each farm are represented in Figure 2. The majority of the samples were negative, which indicates that the herd prevalence is likely very low with no animals in the clinical stage of Johne’s disease. For the samples that had a light, moderate, or heavy result, this indicates that there is some level of infection present within the herd. Due to the largely subclinical nature of Johne’s disease, there is the potential for a small number of animals shedding millions of bacteria into the environment. Samples classified as heavy could be due to one or more “super-shedders” in the herd contributing heavily to the environment.  

Figure 2: Results from Environmental Fecal Culture Samples from Nine Farms

Individual Sample Results and Economic Analysis 

 A total of 442 individual fecal samples were analyzed for detection of Johne’s disease across the eight partner farms. Results by farm are detailed in Figure 3. Of the 442 samples analyzed, 89.8% of the individual samples were negative, 7.0% were suspect, 1.3% were identified as low shedders, 0.5% were moderate shedders, and 1.3% were heavy shedders.  These results did not support our initial hypothesis that cows with low milk production in early lactation could be infected with Johne’s disease and shedding detectable levels of the bacteria. However, the high proportion of negative results could indicate that many farms have successful management practices in place that have reduced their herd prevalence of Johne’s disease.

Figure 3: Individual Johne’s disease test results by farm

Along with the individual test results, each farm received an economic analysis for each cow tested for Johne's disease. The economic analysis tool utilized a series of inputs based on each individual herd's metrics and compared the cow to her herdmates and gives the animal an economic value compared to a replacement animal. This supporting piece of information was provided as additional support to farms for consideration of culling a cow in early lactation if her test result was positive and her economic contribution to the herd was negative. Johne’s test status, milk production, and profitability were provided as supporting evidence that culling an early lactation animal could have a beneficial impact on their herd, both from a disease management and financial standpoint. This economic analysis tool was useful and informed conversations around management and culling decisions with partner farms. Based on individual test results and economic analyses provided, partner farms were willing to cull an animal classified as a "high shedder" in early lactation but were resistant to cull moderate or low shedders, even when the economic analysis indicated they should do so. This was likely due to these animals being early lactation, and partner farms were reluctant to cull animals in early lactation without multiple reasons. This was especially true if animals producing poorly in early lactation were 1st or 2nd lactation animals, as the return on investment has not been achieved for that animal and her potential for production in future lactations high. 

Farmer Focus Groups 

A total of four dairy producers, 3 male and 1 female, from three of the participating partner farms attended the focus group. Herd sizes ranged from 200 to 700 cows. All three farms that participated in the focus group had at least one test-positive cow during the course of the study.  

During the qualitative analysis, two themes emerged: (1) knowledge of Johne’s disease and management practices and (2) financial impacts of management recommendations.  

Theme 1: Knowledge of Johne’s Disease and Management Practices 

One subtheme related to farmer knowledge and management practices surrounding Johne’s disease was identified. A decrease in farmer concern related to Johne’s disease on their own farms was identified among all participants. One participant responded, “we know the disease is endemic in our herd, but we have implemented management practices that allow us to keep it in check.” Participants were aware of Johne’s disease and the impact it can have on the farm, but through increased awareness of the disease and education about best management practices they felt they had the necessary tools to manage the disease.  

Participants also expressed a decreased concern regarding Johne’s disease in the dairy industry as a whole. The consensus was that Johne's disease is less prevalent in herds now than it was nearly 20 years ago and therefore less of a threat to the industry. However, all participants agreed that if a definitive link between Johne’s disease in cows and Crohn’s disease in humans were ever proven, it would become a huge concern throughout the dairy industry.  

Producer responses around animal health concerns showed that other diseases or health concerns were of greater concern as compared to Johne’s disease. Two of the three farms acknowledged that Johne’s disease ranked in the top 5 concerns related to health issues within their herd, while one producer indicated that Johne’s disease was only considered when there was no other apparent reason for illness in a sick animal.  

Theme 2: Financial Impacts of Management Recommendations 

Two subthemes related to financial impacts of management recommendations were identified during analysis. First, the cost of recommended management changes was identified as a barrier to implementing changes. Infrastructure upgrades to improve management are a commonly identified need among dairy farmers in Vermont to improve or alleviate management concerns such as overcrowding or to reduce the spread of disease. The financial investment needed to implement these recommendations is often perceived as too large of a barrier to overcome for many dairy farms. Participants highlighted the need for recommendations that require significant financial investments to show a return on investment and how improvements would lead to increased financial viability for the farm. One participant commented, “Don’t show me what I can gain by implementing something today, show me how much money I've lost because I didn’t do this five years ago.”   

Financial incentives provided to farmers were also identified as a potential way to overcome the barriers to implementing management changes on farms. Participants identified programs within the dairy industry currently in place that provide financial incentives, such as milk quality premiums and grant funds. However, these incentives are not equitable across all farms, with participants identifying the challenging process of applying for and obtaining grant funds that would reduce the financial burden of implementing new practices on the farm. One potential incentive program that gained unanimous support among the participants was for premiums paid directly to producers to certify that their milk was “Johne’s free” if such a program were to be put in place.  

 Johne’s Fact Sheets 

Fact sheets are attached to this report as an information product.  

Discussion

The survey conducted with partner farms at the beginning of this study identified key motivating factors for both management and culling decisions. A key motivation for decision-making and culling was identified to be driven by overall economic impact to the farm. However, when farms were presented with follow-up information following individual testing which included current milk production and an economic analysis, very few farms were willing to cull an animal in early lactation despite low milk production and a negative economic contribution to the herd.  

 Environmental results highlighted that while a herd may not have individual animals that yield a positive test result, there can still be a detectable level of Johne’s disease on a farm. Because of the largely subclinical nature of this disease, many animals that may be infected are not shedding detectable levels of the bacteria; it is possible for the MAP bacteria to be present in the environment but not yet detectable by fecal PCR tests in individual animals. The environmental samples were analyzed via fecal culture, which is the most sensitive and accurate test for detecting Johne’s disease. The downside to this test is that it is more expensive, and results take between six and eight weeks, which make it an impractical choice for individual testing. Most infected herds have a low within-herd prevalence with roughly 30-40% of infected cows shedding the bacterium (Barkema et al., 2010). This further supports a need for educational resources provided to producers that highlight Johne’s disease as an animal health concern and the need for continued management practices that can help reduce the risk of disease in a herd.  

The initial plan to develop a singular approach to identify individual animals for sampling was modified from the original proposal. In the initial stages of developing cut points for production for each farm, it became obvious that due to the different management styles and methods used to manage data on partner farms that cut points determined without producer input would not be a viable method for selecting individual cows for sampling. In addition, the originally proposed method of cut points based on production would not be easily adopted by farms. Instead, criteria for individual sampling were developed using current milk production, change in milk production over time, and producer input. We felt this approach was a more realistic expectation for farms that may adopt this method after the study.  

The individual samples yielded results that were unexpected. The working hypothesis for this study was that the significant stress calving places on a cow would cause her immune system to be weakened and if a cow were infected with Mycobacterium avium subspecies paratuberculosis (MAP), detectable levels of MAP would be present during early lactation. However, individual samples yielded largely negative results. Upon reflection, it seems likely that calving could be the event that precipitates a previously infected animal to progress from the silent stage of infection to the subclinical stage, and that animal may not begin to shed detectable levels of MAP until later in lactation. Throughout the process of identifying and sampling individual cows, it became apparent that many different factors can influence milk production in early lactation or a decrease in production between monthly milk tests. As is common when conducting research on working dairies, there are many confounding variables that can account for variation in milk production. Some examples of these variables are putting cows out on pasture in the spring, group changes, forage and diet changes, and illness. These examples were more apparent in herds that utilized monthly milk testing compared to herds that had daily milk weights from the parlor.  

Follow-up visits with partner farms to present results of individual samples and economic analyses highlighted reluctance to cull early lactation animals. It was expected that farms would be hesitant to cull an animal in early lactation, which was why this study provided three pieces of information as evidence for why a cow was a good candidate for removal from the herd. Farms were generally willing to cull an animal that had a test result indicating they were shedding a high level of MAP into the environment. Only 1.3% of test results were returned as high shedders, and this accounted for a very small number of cows, roughly 1 high shedder for every 75 cows tested. This number sounds innocuous, however a small percentage of cows in a herd diagnosed as high shedders can be responsible for shedding billions of bacteria into the environment and pose a substantial risk of spreading infection to other animals in the herd. The animals selected for individual testing were animals that showed a decrease in production or clinical signs of disease. However, not all animals shedding MAP bacteria have begun to exhibit clinical signs such as decreased milk production or excessive loss of body condition. It is likely that these animals selected for sampling that returned a high shedder test result would not have been identified and removed from the herd until they began to exhibit clinical signs, at which point other animals could have become infected. Individual testing can be useful to identify infected animals before they exhibit clinical signs, but the cost and time associated with collecting the samples have led many farmers to move away from preventive diagnostic testing once it was no longer subsidized. One potential way to address the concern of Johne’s disease prevalence on dairy farms is by conducting routine environmental sampling of the herd, which can help determine if there are heavy shedders present in the herd.  

While the economic analysis tool utilized was designed to highlight the economic value of an individual cow compared to a replacement, it was found that significant drivers of this tool were milk production, days in milk, lactation number, and pregnancy status. The price of replacement animals also increased significantly during this study, which favored a more positive economic value for evaluated cows compared to a replacement. This increase in replacement animal cost may have placed a higher value on keeping marginal animals versus culling. Johne’s test status, milk production, and profitability were provided as supporting evidence that culling an early lactation animal could have a beneficial impact on the herd, both from a disease management and financial standpoint. However, these results highlight the need for a more in-depth financial analysis tool that could take into account the economic impact of Johne’s disease.  

Figure 4: Example economic analysis graph of a cow.

The focus group allowed for more in-depth discussions with partner farms surrounding Johne’s disease and their perceived barriers to implementing management changes. It was not surprising that Johne’s disease was not viewed as a primary concern on participating farms. Individual test results yielded few positive results, and farms had implemented management strategies designed to reduce the risk of infection. An unexpected finding from this focus group was the need for increased facilitation of peer-to-peer learning for dairy farmers. All focus group participants acknowledged that farmers are more likely to implement a new management strategy if they can talk directly to someone that has already done it. During the pandemic there were decreased opportunities for farmers to gather in person to allow for peer-to-peer learning to take place, and these gatherings have been slow to reestablish in recent years. There is an opportunity to provide more in-person opportunities for farmers to gather and share knowledge, particularly in the Northeast where dairy farm numbers are in decline.  

The original fact sheets on Johne’s disease were created in 2009 by Dr. Julie Smith and Rebecca Calder at the University of Vermont. While much of what is known about how Johne’s disease infects an animal and the progression of the disease, there have been updates regarding how the disease is managed in the industry. A significant amount of focus was placed on testing individual animals and culling moderate and high shedders to help identify and remove infected animals from the herd. However, at the time there was support to help defray the cost of testing and veterinary services to encourage farms to implement the test and cull method. Since the end of this program, the test and cull method is no longer the gold standard. More focus has been placed on prevention through management practices. The updated set of fact sheets created will further support education of farmers and service providers, as well as provide veterinarians with a resource to educate their clients. 

A primary limitation of this study was that it was a convenience sample. Many of the participating farms had previously participated in a voluntary Johne’s control program, and therefore had knowledge and experience with the disease. Local veterinarians were used for recruitment, which may have created a potential for bias of herds that veterinarians were concerned were at risk for Johne’s disease. An additional limitation of this study was the small size of farms recruited, with nine farms initially enrolling in the study and a final number of eight farms. This sample size may not be representative of the presence of Johne’s disease on Vermont dairy farms. However, conducting research on working dairy farms and coordinating times to sample cows takes time and effort, and a larger sample size was not feasible given the time and budget constraints of this project. It is possible that were this study conducted in a herd that had a high prevalence of Johne’s disease this culling strategy would be an effective means to control Johne’s disease. However, future studies that target later lactation cows with a sustained decrease in production may be a more practical means to identify and remove positive animals from the herd. While this study did not yield the expected results, further research into the economic impact of Johne’s disease would provide additional support for culling animals with positive test results. The results of this study highlight that the work to educate Vermont dairy farmers during the early 2000’s on the risks and impacts of Johne’s disease were largely successful. Dairy farmers now understand how to identify a cow showing clinical signs of disease, management practices to reduce the risk of introducing Johne’s disease into the herd, and this study was able to further support that these efforts had an impact through individual testing of cows.