2012 Annual Report 1a.Objectives (from AD-416): The NAHMS program includes periodic national commodity studies to investigate current issues and examine general health and management practices used on farms. These studies are driven by industry and stakeholder interest, and collect information that is not available from any other source. 1b.Approach (from AD-416): Activities will include testing of sera from lambs for antibodies to Toxoplasma gondii by using the modified agglutination test (MAT) during the National Animal Health Monitoring System (NAHMA) Sheep 2011 study. 3.Progress Report: Toxoplasmosis is the major cause of economic losses to sheep producers across the U.S. and also a threat to human health. Increased producer education is needed to reduce the prevalence of Toxoplasma gondii in sheep operations nationwide. Blood was collected from 4,009 market age lambs (3-12 months of age) from 359 operations in the 22 largest sheep producing states. Sera were tested for antibodies to T. gondii using the modified agglutination test (MAT). Of all lambs tested, 477 (11.9%) tested positive with a titer of 25 or above. Lambs in the west had the greatest seroprevalence (17.9%) followed by the east (10.6%) and central U.S. (6.1%). The seroprevalence was 13.1% in small and medium operations with 20-499 ewes, and 6.4% in large operations with 500 or more ewes. By flock type, seroprevalence was 13.8% in operations that managed their sheep on pasture compared with 4.4% in open range flocks. Of the 359 operations, 45.4% (163) had at least one seropositive sample. By flock size, operation-level prevalence was greatest among operations with 100-499 ewes (48.6%), followed by operations with 20-99 ewes (45.6%) and 500 or more ewes (35.3%). Operation-level prevalence was greatest among operations in the west (58.8%) followed by the east (42.6%) and central U.S. (31.7%). Nearly one-half (49.3%) of operations that primarily managed their flock on pasture had at least one positive sample. Operation level by management type was: open 37.5%, fenced 37.7%, pasture 49.3%, dry lot 41.2%. Studies have found Toxoplasma titers to increase with age, which may in part account for this difference along with the size, type and location of the flocks of origin.