Convention: Sheep Disease Updates

Sheep Disease Updates Dominate Animal Health Discussions

The Shepherd

The Animal Health Committee session at the ASI Annual convention was packed with updates from industry collaborators.

Dr. Diane Sutton of the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service reported the excellent news that there have been no new cases of sheep or goats infected with scrapie in the nation in nearly two years.

Erica Sanko of the California Wool Growers Association reported on her organization’s successful effort to import FootVax into the United States from its manufacturer in New Zealand. With footrot a top animal health priority for California sheep producers, CWGA applied for a federal research and education permit to import the vaccine as a short-term fix while a domestic-sourced vaccine is being pursued for the long-term.

The association imported 95,000 doses, which were distributed to producers at a cost of $1.25 per dose in 250-dose packs. Orders had to be prepaid, and there were 34 producers participating, representing three states: California, Idaho and Oregon. CWGA has a small carryover of the vaccine available to its members, and is preparing to place its second order. Producers using the vaccine have reported steep declines in the number of sheep showing signs of footrot.

Dr. Maggie Highland of the USDA Animal Research Service presented a short introduction to Mycoplasma ovis in domestic sheep in the United States. The red bloodcell-infecting bacterium M. Ovis can lead to ill-thrift in sheep (which can seem similar to parasite infection or mineral deficiency) and in some animals, death – but not all infected animals will show signs of the disease. Hosts include domestic sheep, goats and white-tailed deer, and its distribution is worldwide. M. ovis is transmitted through biting insects and needle reuse, as well as some transplacental transmission. Abattoirs in some countries condemn infected carcasses because of jaundice, and vaccines have not yet proven successful. The production consequences of M. ovis are currently being examined, Highland said, in conjunction with a three-year research project at the U.S. Sheep Experiment Station.

M. Ovis is an under-recognized but widespread pathogen in domestic sheep in the United States, Highland said, while emphasizing that M. ovis is not to be confused with the respiratory complex Mycoplasma ovipneumoniae.

Dr. Natalie Urie, also with ARS, presented information on M. ovis data collected during the National Animal Health Monitoring System study on the nation’s sheep flocks in 2001 and 2011.

Urie reported that preliminary risk factors associated with M. ovis detection include:

• Flock size: Larger sheep flocks had a higher seroprevalence.

• Region: The central portion of the country in the NAHMS study had higher detection rates.

• Year of blood collection: M. ovis detection rates were higher in the 2011 sampling than from 2001.

• Requirement of preventative health practices (vaccinations, deworming, etc.): Operations with no preventative health practices for new additions to their flocks were 2.1 times more likely to have M. ovis.

• Public lands grazing: Operations that had sheep flocks grazing on public lands were 3.5 times more likely to have M. ovis present in their flocks than other grazing systems such as those who practice shed lambing or pasture lambing. Urie suggested perhaps that’s because these flocks sometimes come in contact with other flocks, or might simply be more likely to have biting insects present that are transmitting M. ovis.

• Vaccinations: Operations that administered vaccines were 1.7 times more likely to have M. ovis than those that did not. This does not mean that vaccines spread or cause M. ovis, but it does mean that producers need to do a better job in changing needles between animals.

After examining detection rates, researchers then looked at preliminary risk factors associated with M. ovis within-flock seroprevelance.

Once again, flock size, region and year of blood collection were risk factors, along with a few others. Operations that had experienced any abortions during the study years had 1.12 times higher within-flock M. ovis seroprevalence. In one odd finding that will require more examination, sheep operations that reported always disinfecting shearing equipment had 1.7 times higher M. ovis seroprevalance rates than those who reported only sometimes or never disinfecting shearing equipment. That doesn’t mean that disinfecting shearing equipment spreads or causes M. ovis.

ARS will continue to analyze results and will report back on findings in the future.

Dr. Christina Cunha of ARS reported on research progress concerning Malignant Catarrhal Fever, a serious and often fatal disease that affects many species, including sheep, cattle, bison, deer, moose and pigs. MCF can be carried asymptomatically by sheep, but causes a usually fatal disease in clinically susceptible hosts.

MCF is a sporadic disease that tends to occur in outbreaks, Cunha said. Sheep need a very high dose of virus to cause death, unlike other species such as bison. There is no vaccine or treatment available to combat MCF.

Cunha recommends that in the event MCF is detected, management options should be focused on separating clinically susceptible and carrier hosts, and production of virus-free carriers. Meanwhile, researchers are focused on production of a vaccine that will stimulate a neutralizing antibody response capable of blocking the virus at the entry site, thus preventing infection and/or disease.

Barber pole worm is a pathogenic gastrointestinal parasite, and thrives in warm, humid climates, but is now present in most states, according to Dr. Joan Burke, ARS research animal scientist, even out west where areas are irrigated. This blood-sucking worm is very prolific and causes great health problems, including anemia, reduced gain, poor performance and health.

Anthelmintics don’t work to control this parasite, so alternative control measures are recommended, but should be selective among flock members. Using a three-way anthelmintic combination, along with copper oxide wire particles increases efficacy, according to Burke. Other control measures included having flocks consume condensed tannin-rich forages, grazing management strategies and genetic selection.

Burke suggested that producers in some regions can move to fall lambing to get away from parasites. Most worm transmission occurs during peri-parturient, so selecting for parasite-resistant ewes during this time is also a good management strategy. Having good stocking rates and optimizing condition and nutrition are also good strategies, while minimizing overall stress for healthier flocks.

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