Effects of visible signs of contagious ecthyma on mass and survival of bighorn lambs.

External signs of contagious ecthyma became common in a population of Rocky Mountain bighorn sheep (Ovis canadensis) in Alberta, Canada, after it attained high density. Between 1990 and 1993, we studied effects of this disease on mass gain and survival of lambs. Prevalence and severity were independent of lamb sex. Lambs with large sores and scabs gained less mass than other lambs and were lighter the following spring as yearlings. There was no significant effect of the disease upon lamb survival, and contagious ecthyma did not appear to play a primary role on the dynamics of the study population.