Toxoplasmosis, caused by Toxoplasma gondii, poses a significant threat to sheep flocks, affecting reproductive performance and meat quality, and leading to economic losses. This study aimed to evaluate the correlation between anti-T. gondii IgG antibodies in the serum and colostrum of naturally infected ewes and to assess passive immunity in newborn lambs. Blood and colostrum samples were collected from 162 ewes and 182 lambs across 20 sheep farms in Paraíba, Brazil. Samples were tested for anti-T. gondii and anti-Neospora caninum IgG using indirect fluorescence antibody tests (IFATs), with titers ≥ 1:64 considered positive. Among the ewes, 45.1% tested positive for anti-T. gondii IgG in serum, with titers ranging from 1:64 to 1:16,384. The colostrum from 94.6% of the ewes also tested positive, although 74% had higher titers in their serum than in their colostrum. Concordance between serum and colostrum was high, with a kappa coefficient of 0.950. Lamb serum showed a perfect agreement with maternal colostrum (kappa = 0.962), demonstrating effective passive transfer of antibodies. This study confirms that colostrum is a reliable matrix for detecting anti-T. gondii antibodies and assessing passive immunity in lambs. The high concordance between serum, colostrum, and lamb titers suggests that IFATs on colostrum can be a practical tool for monitoring maternal antibody transfer, contributing to the better management of T. gondii infections in sheep flocks.

New alternatives for controlling resistant populations of gastrointestinal nematodes are being studied, including the use of plant compounds and biological control with nematophagous fungi. The objective of this study was to evaluate the in vitro anthelmintic effect of linalool and its association with the fungus Duddingtonia flagrans (isolated AC001) in controlling gastrointestinal nematodes in sheep. The ovicidal activity of linalool was assessed via the Egg Hatch Test (EHT), and the larvicidal activity of linalool, alone and in combination with D. flagrans conidia, was evaluated via the Larval Motility Inhibition Test (LMIT) on infective larvae (L3). In the EHT, 100% inhibition occurred (at 1.25 and 2.5 mg/mL), with an LC50 of 0.49 mg/mL. In the LMIT, linalool alone inhibited 100% of larval motility (at 4% and 8%), with an LC50 of 0.42% or 4.2 mg/mL. In the combination of linalool with D. flagrans, there was a significant reduction in larvae, starting at 24 h, with 100% reduction after 14 days, thus being more effective in reducing L3 compared to the use of the fungus alone. It is concluded that linalool exhibits ovicidal and larvicidal activity, and its association with D. flagrans enhances the fungal predation capacity and potentiates anthelmintic efficacy.