Researchers at the University of Wisconsin-Madison are approaching the halfway mark in a nationwide survey of dairy producers that”s part of an effort to prevent Johne”s disease. Cooperating dairy producers will get free confidential testing of their cows, and they”ll be helping to reduce the impact of a disease that costs the U.S. dairy industry hundreds of millions of dollars every year.
“Johne”s is a good candidate for prevention by genetic resistance because vaccines for the disease are only partly effective, and once cattle get the disease there is no cure. The only way to control this disease is to prevent it,” explains dairy cattle geneticist George Shook, who leads the team of UW-Madison researchers. They hope to identify three to five genes that are involved in the resistance and susceptibility to Johne”s disease. Applying this knowledge would allow producers to select AI sires whose daughters are resistant to the disease.
Using tools of molecular genetics, the researchers are genotyping the daughters of 12 prominent Holstein bulls, located in herds throughout the country. The bulls were selected because they have large numbers of daughters — up to 50,000 — in production in herds on the Dairy Herd Improvement program. The bulls themselves are not diseased.
The researchers are contacting herds that have five or more daughters of the 12 bulls (about 10 to 15 percent of DHI herds). “So far we”ve tested close to 4,000 cows. We want to test 6,000 more to reach a total of 10,000. We have a long way to go, but continued good cooperation from producers will help us get there. The more cows we test, the more genes we”ll be able to discover,” Shook says. “We have identified more than 220 disease-positive cows; most of these were not previously known by the producer to be infected. The information allowed producers to take action appropriate to their situation to prevent the spread of disease to uninfected animals.
“We”re making our final contacts with producers now and will complete those contacts by March 2003. When people get our letter and information about the project, we hope that they will reply positively and be willing to sign on to the project,” Shook says.
The research project will pay for the disease testing — a $25 benefit for each cow tested. In addition, for every project cow tested, producers can select another non-project cow for a free test. Test results are returned to producers for use in controlling the disease in their own herds. Shook adds that the results are confidential, and won”t be shared with anyone but the cooperator.
“Herds that know they have animals with Johne”s disease are especially valuable to us and we know that these herds can benefit from the testing that we do,” he says. “We would also like to work with herds that have recently tested in other Johne”s disease programs. In these cases we would need only a blood sample for DNA analysis and the test results for project daughters.
“Herds that don”t know their disease status should participate too. Many of these herds have the disease, but don”t know it. We want to test them, too, for the benefit of our project and to help these herds begin to get a handle on controlling Johne”s disease. Every day that passes, some of the daughters we want to test are being removed from herds, so it”s important that we move ahead as quickly as we can to be able to test as many daughters as possible.”
The project hasn”t gathered enough samples yet to be conclusive, but Shook has already noticed one intriguing result: Prevalence of the disease among bulls” daughters ranges from a low of less than 2 percent to a high of nearly 12 percent. “If these differences stand up through additional testing, we”ll have some interesting and valuable comparisons to explain,” he says.
The data collected during this study will be useful in other areas of dairy health as well. “We”re beginning to understand that the DNA samples we”re collecting will be useful for many more studies beyond genetic resistance to Johne”s disease,” Shook says. “For example, we”ll use these genotypes to search for genes associated with mastitis resistance as measured by somatic cell count and for genes associated with reproductive performance as measured by calving interval or days open. The serum samples we use for disease testing could be used to assay for antibodies to another infectious disease.”
The researchers plan to contact herds in the Eastern states and Wisconsin during November and December, Central states in January 2003, and Western states in February 2003.
The USDA Initiative for Future Agriculture and Food Systems is providing most of the support for this study. The researchers also have received support from National Association of Animal Breeders and a Hatch grant from the UW-Madison College of Agricultural and Life Sciences.