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

Objective 1:

Step 1: Recruit additional partner farms. This project is designed as an on-farm participatory research project. There will be between 4 and 10 farms. Four farms have committed to this project so far, and additional farms will be recruited with the assistance of local veterinarians. We will enroll up to 10 farms of varying sizes, including both conventional and organic herds.

This first objective has been completed. Eight farms, including organic and conventional dairies, have been recruited for this study. Local veterinarians were used to recruit partner farms.

Step 2: Evaluate partner farm perceptions surrounding Johne’s disease and culling decisions in early lactation. We will interview partner farms using the attached interview protocol to understand their current perceptions of Johne’s disease presence on their farm, as well as management strategies related to disease management. In addition, we will ask about their current processes for culling animals and how likely they would be to adopt a new management strategy related to culling in early lactation. The data analysis will involve coding of themes so we can summarize motivations for culling decisions and understand how best to design messaging to encourage on-farm adoption of our proposed culling strategies. This approach is consistent with the theory of planned behavior, which looks at the likelihood for a person to engage in a behavior.

The second objective has been completed using the interview protocol attached. Farmer responses have been given a number in order to maintain anonymity. A variety of responses related to motivations surrounding behavior were recorded. A slightly modified version of these survey questions will be given again at the end of the study to determine whether any changes related to culling behavior and disease management were implemented, as well as knowledge gained throughout the study. The survey results will then be used to help shape our outreach.

Step 3: Determine presence of Johne’s disease within herds. Each herd enrolled in the study will receive a herd-level screening test for Johne’s disease to identify whether there is a detectable presence of the disease within the herd. Pooled fecal samples from individual cows or environmental samples from a minimum of 6 sites on the farm will be tested for the Johne’s organism using a molecular PCR test performed at a veterinary diagnostic laboratory. The most cost-effective testing strategy will be selected for each farm. The test results will serve as a baseline estimate of the level of shedding in the herd and are provided as a benefit for farms participating in the project. Knowing the baseline will be important since we expect that culling will reduce disease presence on these farms over time.

This step has been completed. All farms have had an environmental fecal culture of six individual locations to determine whether there is a presence of Johne's disease within the herd. Environmental results have been presented to each partner farm.

Step 4: Establish production cut points for considering culling. Before implementing new culling decisions, farms will first need to establish cut points for low production based on their herd’s milk production records. To establish cut points, we will use either monthly DHIA milk test information or daily milk weights, depending on the production records used by the farm. For farms that test monthly, we will use week 4 milk production from the previous 12 months to establish benchmarks for each lactation group. Then we will work with each farm to set the amount below the production benchmarks to use as the cut point. Cut points will be determined by lactation group for 1^st lactation, 2^nd lactation, and 3^rd and greater lactation cows. Cows with production below the cut point will be identified for potential culling by the farm. For herds that record daily milk weights, we will monitor milk production for the first 28 days of lactation. In these herds, the culling decision cut point will be when a cow in 1^st lactation has not increased production daily for the first 20 days in milk, or a cow in 2^nd or higher lactation has not increased daily production for the first 28 days in milk. Other health events that can contribute to low production, such as mastitis or transition related issues, will be recorded.   

This step has been completed, although it has been modified from our original proposal of establishing production cut points based on herd production records. In analyzing the production data, it became clear that there was not a "one size fits all" approach to applying production cut points to each farm. Instead, we decided to allot tests based on a percentage of calvings expected within a six month period. From there, we have worked with each farm to establish criteria for selecting animals for individual testing. By looking at herd production data for stage of lactation and parity, cows under 100 DIM and deviating more than -10 pounds from their previous monthly production are selected for testing. This method is combined with producer input based on animals that they determined were not producing as expected in the first 100 days of lactation. We felt that this approach was a more realistic expectation for farms that may adopt these management strategies after the study is completed.

Step 5: Decide how information will be used to influence culling decisions. We will seek to understand how farms feel about culling early lactation animals based on production alone. We will work with partner farms to develop a plan for how they will use production data and test results to make a culling decision.

This step is currently in progress. After each round of individual test results come back, an economic analysis is run for each tested animal and these results are presented to the farm. The farm is able to take that information and decide whether they would like to cull the animal based on the data provided, or for that animal to remain in the herd.

Objective 2:

Step 1: Provide testing to farms. Because farms may not be willing to cull a cow in early lactation based on production alone, we will offer a fecal PCR test to determine Johne’s disease status of animals that fell below established cut points. We have budgeted to allow us to test up to 50 animals per herd or a total of 430 cows over the period of the study. The timeframe for testing will be from September through April, to avoid the confounding influence of heat stress as a cause of decreased production.

The individual testing of cows on partner farms is roughly halfway completed. Testing has been completed on three farms, and we expect to complete the remainder of the individual tests by the end of May 2024.

Step 2: Present test results to farms. There are four possible test result outcomes of a fecal PCR test; high-shedder, moderate shedder, low shedder, and negative. Test results will be presented to the partner farms. Farms will use this information according to the plan developed in objective 1.

Test results are presented to farms after each round of testing. Animals with a high-shedder result are recommended for culling from the herd. Animals with a moderate, low, or suspect (very low positive or contamination) are generally recommended to be retested at a later stage of lactation to see if the results have changed. There are instances when an animal my be a low shedder on one test and then negative on a subsequent test due to ingestion of the MAP bacteria that is simply passing through the animal but not truly infecting them with the disease.

Step 3: Develop partial budgets. A partial budget is useful for understanding the economic benefits of implementing a management change and will be developed to assess the economic benefits of culling low production animals within early lactation. We will present a partial budget specific to each partner farm, which shows the economic costs and benefits of implementing our proposed management change, assuming all else remains the same.

Along with the individual test results, each farm receives an economic analysis for each cow tested for Johne's disease. This economic analysis has a series of inputs based on each individual herd's metrics and compares a cow to her herdmates and gives that animal an economic value compared to a replacement animal. This is a supporting piece of information that may help a farm feel more comfortable culling a cow in early lactation if she has a very negative economic value in the herd. This tool has informed a lot of conversations around management with the partner farms.

Step 4: Reevaluate culling strategy. We will work in collaboration with partner farms to evaluate, based on the available information, whether the initially developed culling plan is adequate or whether it needs to be modified. If the budget has not been exhausted in year 1, we would request a no cost extension in order to recruit additional farms and allow for, at a minimum, herd level screening tests for Johne’s disease and limited testing of individual animals.

Based on our results so far, partner farms are willing to cull an animal classified as a "high shedder" in early lactation, but are more resistant to cull moderate or low shedders, even when the economic analysis indicates they should do so.

Objective 3:

Step 1: Present preliminary findings to farmer groups. We will find opportunities to present our preliminary results at 2 or more producer meetings and share our results with the broader dairy farming community. The purpose of these meetings will be to recruit additional producers to adopt this management change on their farms.

We are planning to host farmer focus groups in the spring of 2024 to take a look at the motivations and barriers to management changes related to Johne's disease control. We will use the information collected at these focus groups to inform our further outreach.

Step 2: Recruit additional farms. Other farms that are interested in adopting and implementing management changes based on preliminary results from this partnership study will be enrolled. (This is dependent on the success of the prior objectives with our partner farms.) We will use the framework established in the previous two objectives to implement the proposed management changes with these additional herds. If the budget allows, we will provide the same herd level screening test for Johne’s disease.

Step 3: Provide framework. Create a digital copy of the framework used that will be located online for farms to easily access. This will allow more farms, regardless of location, to be able to adopt the framework on their own farm. We believe this management approach will be applicable across all types of dairies.

Step 4: Evaluation of success. Project leaders will evaluate the satisfaction of participating farmers with this approach to controlling Johne’s disease and enhancing profitability.