Interaction between Duddingtonia flagrans and dietary coccidiostats in lambs in reducing the development of Haemonchus contortus larvae.

Providing dietary spores of Duddingtonia flagrans leads to fewer gastrointestinal nematode (GIN) larvae on pasture, but little is known about its interaction with dietary coccidiostats. The objective was to determine the efficacy of D. flagrans fed to sheep with or without coccidiostats, decoquinate (Study 1 and 2) or lasalocid (Study 3) to reduce the number of GIN larvae (predominantly Haemonchus contortus) in feces. All studies used a 2 × 2 factorial design (± D. flagrans × ± coccidiostat). Study 1: An in vivo experiment used 8 lambs/treatment and the recommended 5 × 105 chlamydospores/g carrier, but a post-study analysis indicated the package used contained 10-fold fewer spores. There was no reduction in cultured larvae associated with D. flagrans. Studies 2 and 3: anthelmintic-treated lambs were fed a supplement with coccidiostat (C+; decoquinate or lasalocid in Study 2 or 3, respectively) or without (C-) for 7 (Study 2) or 14 (Study 3) days before fecal collection; within diet, D. flagrans was administered (DF+) daily or not (DF-) 1-3 days before fecal collection. Feces were cultured on agar plates for 7 days at 2 g/plate + 300 L3 of H. contortus or 5 g/plate + 1000 L3 (n = 3-4 plates/lamb) at 25°C. On the 2 g plates, D. flagrans reduced L3 recovery (P < 0.001) without an effect by coccidiostat in Study 2 (P = 0.38) or a slight increased recovery (P = 0.05) in Study 3, and no interaction between D. flagrans and coccidiostat. On the 5 g plates, D. flagrans reduced larval recovery (P = 0.001) and there was no effect of lasalocid or any interaction detected. Using these methods, dietary coccidiostats did not impair the action of D. flagrans (5 × 105 chlamydospores/g) on reducing infective larvae in feces.