Prevalence and effect of subclinical ovine progressive pneumonia virus infection on ewe wool and lamb production

Abstract

Summary The prevalence of infection with ovine progressive pneumonia (opp) virus and its effects on ewe wool and lamb production were investigated in a flock of 2,976 ewes of 6 breed types (Rambouillet, Targhee, Columbia, Polypay, ¼ cross Finnsheep, and ½ cross Finnsheep). Prevalence of seropositivity was significantly (P ≤ 0.01) lower among Rambouillet and Targhee breeds (44 and 42%, respectively), intermediate in Polypay, Columbia, and ¼ cross Finnsheep (approximately 53%), and higher among ½ cross Finnsheep (62%). Seropositivity increased with age in all breed types from ll% at l year of age to 93% at ≥ 7 years of age. Lateral disease transmission is indicated by linear increase of seropositivity prevalence with increasing age, including that in sheep > 6 years old. Subclinical infection with opp virus had no apparent detrimental effect on number of lambs born, lamb viability, birth weight, number of lambs weaned, or growth rate of single and twin lambs, compared with findings for noninfected sheep in the same flock. Mature ewe body weight and grease fleece weight did not differ between subclinically infected seropositive and seronegative ewes. Subclinical infection with opp virus does not appear to have an adverse economic effect on ewe wool and lamb production. Culling rate attributable to clinical manifestation of infection with opp virus must be accurately determined before the true effects of virus infection on production can be determined and an eradication program can be recommended.