Linda Benedict, Owens, William E. | 3/11/2009 7:25:35 PM
William E. OwensMycoplasma mastitis is a unique form of mastitis, which is an inflammation of a cow’s udder. Mycoplasma species differ from the majority of bacteria that cause mastitis by having unique growth requirements and physical characteristics that make them difficult to detect and treat once detected. Mycoplasma mastitis infections do not respond to antibiotic therapy using antibiotics currently available, so no effective therapy exists. In addition, growing these organisms in the laboratory requires specialized media and atmospheric conditions. These difficulties often delay diagnostic efforts and management response to this type of mastitis, magnifying the impact an outbreak has on a dairy herd.
In 2002, the National Animal Health Monitoring System (NAHMS) Dairy Study assessed the prevalence of mycoplasma in bulk-tank milk from 21 states across the United States. Results indicated that 7.9 percent of dairy farms tested positive for mycoplasma from a single bulk-tank sampling using standard culture methods. Sixteen of the 21 states tested had at least one dairy with a positive mycoplasma bulk-tank culture.
History of the Louisiana Outbreak
Mycoplasma mastitis was first detected in Louisiana in September 2002. The positive dairy farm was suffering a severe outbreak of clinical mastitis. Culture for mycoplasma was done as a last resort after routine culture techniques failed to identify a cause. As a result of this initial outbreak and because of the potential for serious economic loss associated with this type of mastitis, all the dairy farms in the state were screened for mycoplasma mastitis by bulk-tank culture. This screening identified an additional 12 dairies (2.8 percent) as having mycoplasma in bulk-tank milk. Cows with confirmed cases of mycoplasma mastitis were isolated from five of these herds.
The statewide bulk-tank results prompted a rapid and unique response from several diverse groups to address the problem. Research scientists and extension specialists from the LSU AgCenter led meetings with dairy producers, dairy fieldmen, the Louisiana Department of Health and Hospitals and the Louisiana Department of Agriculture and Forestry (LDAF). These meetings were held to teach the participants about this type of mastitis and to discuss possible courses of action to deal with it. These meetings led to a program to combat this threat.
Louisiana dairy producers agreed to pay $15 a month to help defray the cost of this program, which consisted of a schedule of monthly bulk-tank cultures from each dairy farm in Louisiana. Bulk-tank samples were collected by milk haulers and transported within 48 hours by LDAF personnel to the Mastitis Research Laboratory at the LSU AgCenter’s Hill Farm Research Station at Homer. Once delivered to the laboratory, samples were immediately cultured for mycoplasma and routine mastitis pathogens typically found by such culture. These routine organisms include Staph. aureus, Strep. agalactiae, Streptococcus species (environmental streptococci), coliforms (primarily E. coli and Klebsiella species) and other pathogens.
When a suspected mycoplasma herd was identified, a confirmatory bulk-tank sample was collected as soon as possible from the suspect dairy and cultured to confirm the presence of mycoplasma. If confirmatory tests proved positive, efforts were made to help the dairy producer identify infected cows. In many cases, composite samples of the entire herd were collected and shipped to the Mastitis Research Laboratory where samples from each cow were cultured.
LSU AgCenter research and extension personnel worked in conjunction with dairy fieldmen, veterinarians and dairy producers to devise management strategies to eliminate mycoplasma mastitis from the affected herd. In addition, LDAF established regulations to reduce the possibility of cows from infected herds being sold to uninfected herds. Once a herd was confirmed positive for mycoplasma mastitis, cows from that herd were restricted to sale for slaughter only. Six consecutive negative monthly bulk milk samples were required to remove a herd from this restriction and allow the sale of cows for dairy use.
Results of the Louisiana Mycoplasma Program
Monthly bulk milk analyses revealed mycoplasma in at least one bulk tank for 12 of the 20 months tested. The greatest number of mycoplasma-positive dairies occurred in the first three months of the program, with sporadic outbreaks occurring randomly thereafter. Twenty-four bulk milk samples were positive for mycoplasma during the monthly sampling phase of the program. Of the 24 mycoplasma-positive samples, four were repeat positive dairies, so a total of 20 dairies tested positive for mycoplasma during the period. Fourteen dairies were confirmed positive by repeat sampling. Seven of those 14 dairies submitted samples from individual cows for culture. A total of 1,025 cow samples were evaluated, and cows positive for mycoplasma were isolated from four dairies. All dairies confirmed positive for mycoplasma and placed on restricted status were subsequently cleared of mycoplasma status, and restrictions were removed by virtue of six negative bulk-tank samples.
Figure 1 shows the distribution of all mastitis pathogens present in bulk-tank milk during the program. Staphylococcus aureus was the most frequently isolated major pathogen, with 51 percent of the tanks testing positive for this pathogen. Staph. aureus and environmental streptococci were present together in 21 percent of the samples.
In 2006, the program shifted to a quarterly rather than monthly sampling schedule. A total of 545 bulk-tank samples were collected in 2006, and three (0.5 percent) tested positive for mycoplasma.
Results indicate that mycoplasma mastitis is present and an ongoing problem for Louisiana dairy producers. While the total number of dairy farms testing positive in any month did not exceed 2 percent, the total of 14 dairies confirmed positive for mycoplasma during the course of the program represents approximately 5 percent of the dairies in the state. This compares favorably to the 6.6 percent of positive dairies reported for the South in the 2002 NAHMS survey. It is noteworthy that after the initial catastrophic outbreak in one dairy, no other dairy suffered similar losses.
Early detection because of the monthly monitoring program allowed for quicker intervention and allowed dairy producers to cull cows and eliminate infections before they sustained major losses.Also, the publicity generated by first meeting to discuss the problem and then involving dairy producers in planning the program helped heighten awareness of this type of mastitis. The heightened awareness helped producers, veterinarians and dairy fieldmen be more aware of proper management procedures to control and prevent this type of mastitis. The 2006 quarterly culture results indicate this program has substantially reduced mycoplasma mastitis in Louisiana to 0.5 percent from an initial incidence of approximately 2.8 percent.
In addition to the mycoplasma culture information generated by this program, dairy producers also benefited greatly from bulk-tank information on other types of mastitis pathogens. Each dairy bulk-tank sample was cultured, and the types and amounts of various masti mastitis pathogens were recorded. Extension agents and dairy specialists provided this information to dairy producers. This appears to be the only statewide program that provides producers with continuing mastitis results on both mycoplasma and other more routine mastitis pathogens. Such monthly information helps producers monitor their overall mastitis situation and make management changes to control emerging problems before they have a major impact. Louisiana is currently continuing the quarterly phase of the monitoring program. The restrictions established by LDAF will continue to remain in effect, and cows from dairies with mycoplasma will not be sold other than for slaughter.
This program can serve as a model for similar control programs in other states.
William E. Owens, Professor, Hill Farm Research Station, Homer, La.
(This article was published in the winter 2009 issue of Louisiana Agriculture.)