I still have more notes to share from the KHSI Expo! Another speaker we heard from was Dr. Lynn Hermann-Hoesing, from the USDA-ARS-Animal Disease Research Unit at Washington State University. Her team is doing research on Ovine Progressive Pneumonia Virus, or OPPV. It is a costly disease that is likened to AIDS in humans- slowly progressive, it robs ewes of thriftiness, and eventually leads to premature death.
One in five sheep in the U.S. are infected, and one in three on the open range. There is correlation to flock size, larger flocks have a higher incidence of OPPV. It is estimated that OPPV costs the sheep industry about $2.7 million annually in lost productivity. The problem with OPPV is that it is often not overtly noticeable to the shepherd, but a flock will experience a smaller, less healthy lamb crop, and ewes that do not live a normal life span. So, the disease is of grave concern to the industry, and is often referred to as the “silent thief.”
OPPV is transmitted “horizontally”- from ewe to ewe; and is thought to be transmitted to ewe lambs not from their mothers directly, but rather after they are weaned and re-introduced to the flock. (This is new information from yet-unpublished research.) It’s a genetic affectation caused by a virus, and is irreversible; i.e. untreatable. Clinical signs only manifest in about 30% of affected ewes, and are not seen until the ewe is 4-6 years of age. When present, the signs are labored breathing, hard udder (mastitis), lameness and swollen joints (arthritis), productivity decrease with age, wasting, and occasional neurological problems.
Currently, the recommendation for controlling OPPV is to test annually (or twice yearly) for five years. Affected ewes can be retained and continue to be bred as long as they are productive and not showing serious clinical symptoms, with the plan of eventually culling them. But they must be kept isolated from the unaffected animals in the herd to prevent transmission. Tests run about $5/sample. So, given the cost and difficulty in maintaining two separate herds, many/most producers have not embraced this method of containment, to date.
Dr. Hermann-Hoesing’s team is working on a DNA test for OPPV, that would offer similar benefits as the scrapie DNA test. This would allow producers to test each animal only once in its lifetime, and progressively breed away from OPPV susceptibility, at a much lower cost than the current method. Their research is currently focusing on the Rambouillet, Columbia and Polypay breeds.The hope is to make progress there, and expand the research to include other breeds in the future.
This presentation sparked a lot of discussion and lively debate amongst the KHSI members in attendance. There is frustration felt amongst the few breeders who are following the recommended OPPV testing program, in that they are very limited in which other breeders from whom they can purchase ewes, because so few others are in the program. And, because they must pass some of this cost on in their sale animals, it makes it hard for them to compete with their non-testing peers. Some feel that KHSI should mandate OPPV testing amongst its membership, or those who register animals. But given the limitations of the current recommended program, this seemed to be very controversial and not widely agreed upon.
I currently have chosen not to test, for these very concerns. The $10/year per ewe doesn’t seem so bothersome, as I could consider it an investment in future flock productivity, and also in marketability of my animals. But, I don’t have the means to separate affected ewes, so I would have to cull them immediately upon finding out they were positive, which would be costly in another sense. For now, I’m crossing my fingers that a DNA test will arrive on the scene soon.
What are your thoughts on OPPV?