By Susan C. Kahler
Practitioners attend continuing education meetings for two reasons, in Dr. John Ferry's estimation: to get the most current scientific knowledge on a subject, and to find out what their colleagues in practice are doing to implement that science.
This philosophy guided the 2005 program committee, chaired by Dr. Ferry, in designing the CE program for the American Association of Bovine Practitioners annual conference.
Mycoplasma: a ubiquitous infection
"In the general session on Mycoplasma, we had three of the world's leading experts talk about the current scientific knowledge, and then we had three practitioners talk about how they implement their programs," Dr. Ferry said.
Dr. R. F. Rosenbusch of Iowa State University gave a presentation on transmission of M bovis and resulting syndromes such as mycoplasmal mastitis, pneumonia, polyarthritis, and middle ear infections. Poor response to treatment and limited effectiveness of prophylaxis make these infections an ongoing concern. Dr. Rosenbusch described how modes of transmission of the various syndromes make certain age groups of dairy and beef cattle susceptible. Besides the nasal, intramammary, and oral routes, colostral transmission is suspected. The disease is more common in young and stressed animals. Transmission can occur regardless of age or health, and not all infected cattle will get sick. Dr. Rosenbusch said not to expect the vaccine to protect against transmission. "As we control Johne's disease, we need to find control strategies that do not interfere with M bovis," he added.
The Mycoplasma session shifted from transmission to prevention with Mary B. Brown, PhD, of the University of Florida. Culturing is the most common method of diagnosis, she said, but it is not always performed on clinical samples unless practitioners request it. Dr. Brown said it's important to determine the species of mycoplasmal organisms to rule out nonpathologic species. Polymerase chain reaction assays can be done instead, directly from a sample or after enrichment. Because PCR assays are not used widely in North American laboratories, she recommended requesting susceptibility/specificity data. For herd surveillance, the antibody-based ELISA determines exposure vs. infection. Dr. Brown said that an increased number of herds have mycoplasmal mastitis, and the National Mastitis Council and the AABP have excellent guidelines for use in testing, control, and prevention.
The program moved on to treatment of mycoplasmal infections. Roger D. Ayling, PhD, of Weybridge Veterinary Laboratories Agency in Surrey, U.K., discussed susceptibility of field isolates and outcome of treatment. He focused on M bovis as a cause of calf pneumonia worldwide and M mycoides subspecies mycoides small-colony type, which causes contagious bovine pleuropneumonia in Africa. It's difficult to control Mycoplasma spp through antimicrobials, Dr. Ayling said as he showed a chart listing susceptibilities to 21 antimicrobials. For M bovis, he said, a combination of culling, vaccination, and antimicrobials might be advisable. Although treated animals may appear to have recovered, they can relapse and be infective carriers. "We need rapid, accurate, and cheap diagnostic tests; effective treatment regimens; improved antimicrobials with short withdrawal periods; and cheap effective vaccines," Dr. Ayling said.
Next, three practitioners shared their experiences with M bovis outbreaks.
Dr. Jan C. Gawthrop focuses his North Manchester, Ind., practice on the care of calves up to five months of age. "Mycoplasma bovis attacks us," he said, "and it never lets up." Infection appears at around 14 days of age. Feeding of contaminated colostrum or unpasteurized waste milk, wet times of year, and poorly ventilated barns are factors. One of Dr. Gawthrop's messages is to be alert for ear droop in a calf at rest as an early sign of M bovis infection. Taking a lesson from swine veterinarians, he suggested advising clients to practice all in/all out management to control disease. He recommended early detection, early and prolonged treatment, good management, and if needed, vaccination of young calves while on milk and again when they are older.
Dr. Peter Kotzeff of Chesley, Ontario, Canada, described Mycoplasma in beef cattle in Ontario and the insidious onset of a chronic, progressive pneumonia that some call chronic pneumonia/polyarthritis syndrome. In his area, it is referred to as the new reality in high-risk cattle. The search for new vaccines and antimicrobials has been disappointing, he said, but it continues. Dr. Kotzeff summarized three alternatives for dealing with the situation: (1) upgrade to lower-risk cattle; (2) institute management changes that include a good caretaker, fungicide use, ample bunk space, yard management, and bedding packs; or (3) accept the situation and "apply Band-Aids."
Dr. Fred J. Muller, who is with a group practice in central Washington state, shared his experience with an M bovis mastitis outbreak in a 1,500-cow Holstein herd. His talk focused on the factors that determine whether a single infection will escalate into a major outbreak in a herd. Dr. Muller said the milking, sanitation, and hospital procedures used by a dairy are the primary determinants. Even closed herds develop mycoplasmal infections sometimes, but Dr. Muller said to be vigilant and not let the situation smolder. "The veterinarian needs to get to the location and look at procedures when there's a Mycoplasma outbreak," he said. These infections are seen most often in herds with replacements from unknown sources, Dr. Muller said. He recommends culling all infected animals.
The Mycoplasma theme crossed over into the AABP feedlot sessions, where Dr. Ted Clark of Saskatoon, Canada, gave an update on pathogenesis and lesions.
From Veterinary Services
Leading off the first AABP general session in Salt Lake City was Dr. John R. Clifford, deputy administrator of Veterinary Services in the Department of Agriculture's Animal and Plant Health Inspection Service. He reported on the status of programs Veterinary Services coordinates for bovine spongiform encephalopathy, brucellosis, tuberculosis, Johne's disease, cattle fever tick, and foreign animal diseases, as well as regulations and trade issues. Dr. Clifford said veterinarians really are the first line of defense and constitute about a third of his agency's 1,700 to 1,800 employees. Vaccines for foot-and-mouth disease and avian influenza are being stored in the National Veterinary Stockpile, he noted. Dr. Clifford also discussed the network of state diagnostic laboratories Veterinary Services has been developing.
Dr. Clifford summarized the components of the National Animal Identification System and reported that it's operational in all 50 states and two U.S. territories, and for five American Indian tribes. The NAIS cattle working group recommends radio frequency identification as the preferred technology. Public comments to the agency indicate that most producers favor a private tracking system.
Veterinary Services will be taking a closer look at brucellosis surveillance and how to retarget it to find the last vestiges of the disease.
Relative to cattle fever tick, Dr. Clifford would like to move the U.S-Mexico buffer zone into Mexico to keep the tick out of the United States. Challenges include acaracide resistance and the prevalence of white-tailed deer and other wildlife as alternative hosts.
Commenting on depopulation, Dr. Clifford said 10 to 20 years from now, it will no longer be acceptable—from animal welfare as well as economic standpoints—to kill thousands of animals, and it's important to think about this now.
By the end of calendar year 2005, he said APHIS will publish the long-awaited, proposed rule seeking public comment on the new two-tiered National Veterinary Accreditation Program that requires supplemental training and offers specializations.