Incidence of infection in 39-month-old ewes with TMEM154 diplotypes "1 1," "1 3," and "3 3" after natural exposure to ovine progressive pneumonia virus

Authors: Leymaster, Kreg; Chitko-Mckown, Carol; Heaton, Michael - Mike

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2014
Publication Date: 1/1/2015
Publication URL: http://handle.nal.usda.gov/10113/62238
Citation: Leymaster, K.A., Chitko-McKown, C.G., Heaton, M.P. 2015. Incidence of infection in 39-month-old ewes with TMEM154 diplotypes "1 1," "1 3," and "3 3" after natural exposure to ovine progressive pneumonia virus. Journal of Animal Science. 93(1):41-45.

Interpretive Summary: Ovine progressive pneumonia is an incurable, slow-acting, wasting disease that affects sheep production in many countries. A decrease in ewe productivity, increased labor requirements, and premature culling or death of breeding stock make ovine progressive pneumonia one of the most costly sheep diseases in the United States. There are no effective vaccines or treatments, but a gene that affects susceptibility to infection was investigated. Sheep with one or two copies of an unfavorable form of the gene had infection rates of 88% at 39 months of age compared to 10% for other sheep. Selection and mating strategies can be used to produce sheep that are genetically less susceptible to this disease, improving health of sheep and increasing profits for producers.

Technical Abstract: Production and well-being of sheep and goats in many countries are harmfully impacted by small ruminant lentiviruses (SRLV) that cause incurable, progressive diseases. Susceptibility to ovine progressive pneumonia virus (OPPV), the North American form of SRLV, is influenced by variants of the ovine transmembrane protein 154 gene (TMEM154). The experimental objective was to estimate additive and dominance effects of TMEM154 haplotypes 1 and 3 on susceptibility of breeding ewes to infection following natural exposure to OPPV from birth to 39 mo of age. Sires and dams were heterozygous for TMEM154 haplotypes 1 and 3, producing ewe lambs with diplotypes “1 1”, “1 3”, and “3 3”. These lambs were raised by mature, infected dams to ensure natural, maternal exposure to OPPV. Ewe lambs (n = 108) were kept for breeding and joined an infected flock of ewes to guarantee natural, nonmaternal exposure to OPPV. Ewes were bred to lamb at 1, 2, and 3 yr of age. Serum samples were collected at breeding, 1 mo before lambing, and shortly after weaning each yr to monitor infection status to 39 mo of age. During the experiment, nine of the 108 ewes died while uninfected and data collected on these ewes were not analyzed. Infection status of the remaining 99 ewes at 39 mo of age was analyzed using logistic regression procedures. Effects of ewe type of birth, ewe type of rearing, and breed type of dam were not detected (P > 0.10), and the estimated sire variance component was nil. Ewe diplotype affected infection status (P < 0.0001), as did additive (P < 0.0001) and dominance (P < 0.0022) effects. Predicted probabilities of infection for ewes with diplotypes “1 1”, “1 3”, and “3 3” were 0.10, 0.88, and 0.89, respectively, and confidence intervals for diplotypes “1 3” and “3 3” were distinct from “1 1”. Haplotype 3 was completely dominant to haplotype 1 at 39 mo of age. The probability of infection for ewes with either diplotype “1 3” or “3 3” averaged 8.5 times that of ewes with diplotype “1 1”. Diplotype “1 3” and “3 3” ewes were highly susceptible to nonmaternal transmission of OPPV, in contrast to diplotype “1 1” ewes. Therefore, the distribution of ewes with diplotypes “1 1”, “1 3”, and “3 3” within a flock will influence the number of infections caused by each route of transmission. Selection and mating strategies can be implemented to produce sheep that are genetically less susceptible to OPPV infection.