Researchers provide updates on prevention, vaccination, transmission, detection and nutrition.
By Emma Wall
Herd health – in particular Johne’s disease – was a major topic during the 2010 American Dairy Science Association/Poultry Science Association/American Society of Animal Science (ADSA/PSA/ASAS) joint annual meeting in Denver, Colo.
By now, the basics of Johne’s disease (paratuberculosis) should be well known. The infectious bacterial disease is caused by the bacteria Mycobacterium avium ss. paratuberculosis. The University of Wisconsin-Madison’s Johne’s Information Center estimates up to two-thirds of all U.S. dairy herds have at least one infected animal. Although young stock are more susceptible to infection, older cattle can also be infected.
The disease continues to pose big challenges for dairy producers. First, animals can become infected, and infect other animals, for years before they show any symptoms. Second, current detection methods are not always accurate, costing the producer both time and money. By some estimates, the disease costs dairy producers at least $200/cow/year, mainly due to decreased milk production long before other symptoms become apparent.
Ongoing Johne’s disease research presentations at the ADSA/PSA/ASAS meeting focused on three main topics:
1) Understanding transmission
2) Prevention and vaccine development
3) Current and new detection strategies
Pennsylvania State University Research showed there are different strains of Mycobacterium paratuberculosis, and these strains affect Holstein cattle differently. Specifically, strain 2 seemed to be more virulent than the others. If strain identification is incorporated into future disease detection methods, producers might be able to fine-tune prevention strategies based on the strains present in their herds.
Research from the W. H. Miner Agricultural Institute showed Mycobacterium avium ss. paratuberculosis, if present in manure used for fertilizing crops, has the potential to infect animals consuming the feed. Producers of infected herds will need to consider this as a potential area of disease transmission when establishing prevention protocols.
Researchers at Texas A&M discovered some of the genes involved in the invasion and persistence of Mycobacterium paratuberculosis in the intestine. Their study may lead to specific targets for Johne’s disease treatment.
Prevention, vaccine development
Researchers with the USDA’s National Johne’s Demonstration Herd Project evaluated Johne’s disease transmission risks in common cattle housing systems. The research looked at calving areas, and pens for pre- and post-weaned heifers, bred heifers, cows and bulls across 62 dairy and 20 beef farms over a 6-year period.
On beef farms, calving and pre-weaned heifer areas were the highest risk areas for disease transmission and the best places to focus on prevention.
However, on dairy farms, the calving area alone seemed to be the most important. They found the best prevention strategies on dairy farms were to:
• make sure udders and legs of cows in the calving area are clean
• use individual animal calving areas or allow fewer animals in the calving area
• prevent Johne’s disease clinical or suspect animals from entering the calving area
Cornell University researchers used mathematical modeling and predicted keeping calves away from shedding animals, combined with culling positive animals, was the most effective strategy for preventing new infections.
Research from the University of Minnesota argued that although young stock are susceptible, disease transmission in adult animals should also be an area of focus when developing prevention strategies. This is supported by Cornell research showing adult animals can be infected by so-called “super shedders” – animals shedding a very high bacteria levels in manure.
Vaccine development seems to be a very active area of study right now. Researchers at Washington State looked at the potential for using a protein on the surface of Mycobacterium paratuberculosis as a vaccine and found, unfortunately, it did not induce a strong enough animal immune response to be effective. However, calfhood injections with the mutant form of the bacteria did not lead to an infection, and researchers are actively pursuing the idea of using this mutant as a vaccine.
Cornell researchers investigated the use of a different mutant as a vaccine. Preliminary experiments on mice showed it partially prevented disease.
Another group at the University of Minnesota looked at the effectiveness of vaccination against Johne’s across three dairy herds from 2005-2009. They found that although fewer vaccinated animals tested positive for the disease, vaccination had no effect on overall lactation or breeding performance. In contrast, other University of Minnesota research showed vaccination protocols reduced herd-level financial losses.
Researchers in India are looking at a new vaccine, developed for goats, that seems to be very effective at preventing Johne’s in both goats and sheep. Their data, although preliminary, show this vaccine may also be effective in dairy cows.
Tri-Lution, a microbial feed additive, has the potential to relieve some of the negative effects of Johne’s disease in infected herds, according to research presented by the product’s manufacturer, Agri-King. The company reported that supplementation with Tri-Lution not only increased milk production, but also decreased bacteria shedding in manure. Therefore, the product has the potential to decrease costs associated with the disease by alleviating some of the milk loss, and by decreasing potential infection rates. This seems to be a pretty new concept though, so more research is needed.
Current, new detection strategies
Researchers from Michigan and Switzerland presented information on a new, high-throughput assay for detecting Johne’s in milk samples. The method is based on an enzyme-linked immunosorbent assay (ELISA) already in use. The researchers described a new, fully-automated system capable of running more than 1,000 samples per day, adding efficiency and speed. If adopted, this could save producers money and time, since the lab can turn the samples over much faster.
At the University of Tennessee, scientists are trying to improve the sensitivity of ELISA. Their results show the potential for improving these tests by detecting new proteins that are found on the membrane of Mycobacterium paratuberculosis.
Although ELISA on blood or milk samples is often used to detect disease, researchers at Purdue University reported fecal sample culturing is the most accurate method to detect animals actually shedding the disease.
Several researchers reported a more sensitive method of disease detection is real-time quantitative polymerase chain reaction (PCR). This method uses DNA amplification to detect and amplify DNA from Mycobacterium paratuberculosis. If it isn’t present in the sample, nothing will amplify. It is more sensitive than other methods, and faster. A few research groups argued this method’s high sensitivity could make it the new “gold standard” for detecting Johne’s disease.
Take home messages
• The calving area is consistently the highest area of risk for disease transmission. Have strategies in place to decrease the risk of infecting new animals.
• Currently, vaccines available for prevention of Johne’s do not always produce consistent results. They have different efficacies on different herds, and don’t always protect animals from infection or shedding. Nevertheless, vaccines may reduce shedding and severity of the disease, so they are probably still cost effective. New vaccines are being tested and hopefully better ones will become available.
• If your herd is infected, there may be nutritional products on the market that can alleviate the effects of Johne’s on lactation performance. Ask your nutritionist.
• Finally, there are several methods of detection available. Work with your veterinarian, test your herd regularly, and encourage the testing laboratory to use cutting-edge detection techniques.
For more information on Johne’s disease, visit:
• USDA’s Animal & Plant Health Insection Service website: http://nahms.aphis.usda.gov/jddh
• the University of Wisconsin-Madison School of Veterinary Medicine Johne’s Information Center website: www.johnes.org
• the National Johne’s Education Initiative website: http://johnesdisease.org
Essential oils, probiotics among other topics
Essential oil research is a hot topic. Using essential oils as feed additives has shown the potential to improve lactation performance of dairy cows and also to increase weight gain and health of calves. This year, research from several institutions looked at the potential of using essential oils in place of antibiotics for both preventative and treatment strategies. Results look promising, and research is ongoing.
Probiotics, also a hot research topic, were covered in an animal health section. Researchers from the University of Alberta reported intravaginal treatment of pregnant cows with probiotics during the transition period improved the health status the cow, and also newborn calves. Treatment of lactating cows with probiotics was shown to decrease the risk of sub-clinical mastitis, increase feed intake and milk production, and improve overall immune status.
Feeding a low-energy diet during the dry period may prevent metabolic disorders in dairy cattle. Research from the University of British Columbia showed that cows fed a low-energy diet (NEL=1.34 Mcal/kg) for three weeks prior to calving had lower dry matter intake, and fewer were diagnosed with subclinical ketosis than cows fed a traditional close-up diet.
Corn silage harvest dry matter alters milk yield. Researchers from Illinois State University found that compared to corn silage harvested at optimum dry matter content (between 33%-36% for the hybrids used in their study), corn silage harvested at 30% dry matter resulted in 5% to 13% less milk per ton and 7% to 25% less milk per acre. The research could impact corn silage hybrid selection.
Increased feed bunk stocking density increases the social aggression of postpartum dairy cows. Consistent with previous observations in transition cows, research from the W. H. Miner Agricultural Research Institute showed that lactating dairy cows increase aggressive behavior during overcrowding. The researchers suggest future work to look at the relationships between overcrowding, clinical illness and feed bunk competition.
For more information on topics covered at the 2010 American Dairy Science Association meeting, go to: http://adsa.psa.ampa.csas.asas.org/meetings/2010.