Gene Discovery Leads to New OPP Test
By Sandra Avant
A new test is available to help sheep producers identify animals at high risk for ovine progressive pneumonia (OPP), thanks to U.S. Department of Agriculture (USDA) scientists.
An incurable, wasting disease, OPP affects millions of sheep worldwide. Infected sheep are less productive and have fewer lambs. In addition to pneumonia, animals show signs of lameness and “hard bag” syndrome, which causes udders to become hard and produce little milk.
Agricultural Research Service (ARS) scientists at the Roman L. Hruska U.S. Meat Animal Research Center (USMARC) in Clay Center, Neb., found that the gene TMEM154 affects susceptibility to OPP virus infection in sheep. Working with researchers at other ARS laboratories and a commercial company, they developed a commercially available genetic test. ARS is USDA’s chief intramural scientific research agency.
Microbiologist Michael Heaton, geneticist Kreg Leymaster and their colleagues in USMARC’s Genetics, Breeding and Animal Health Research Unit looked at the prevalence of infection in USMARC breeding stock in blood samples of infected and uninfected sheep collected over the years from the entire flock. They designed a genome-wide study to test for sheep genes associated with OPP and discovered the TMEM154 gene influences OPP virus infection.
Three major forms of TMEM154, called haplotypes 1, 2 and 3, were in 97 percent of the more than 8,000 sheep tested. Haplotypes 2 and 3 were strongly associated with OPP virus infection and considered highly-susceptible forms of TMEM154. Only one copy of either haplotype 2 or 3 was needed to increase the risk for OPP virus infection, and ewes with two copies of haplotype 1 were significantly less likely to be infected.
However, OPP virus is highly adaptable and affects flocks differently, scientists caution. Therefore, selection for TMEM154 haplotype 1 may not reduce infection in all production environments.
Producers can use the test to detect sheep that are genetically less susceptible to OPPvirus, decrease the risk of animals becoming infected, and select breeding stock with low-risk genetic factors, thereby reducing the prevalence of the virus in flocks.