Fig. 1

A, B Process used in the laboratory to develop decoquinate-resistant strains by gradually increasing the drug level (A) and identifying the Eimeria species isolated from the SC strain by PCR (B). Eimeria maxima US and AUS primers were designed based on internal transcribed spacer 1 (ITS-1) sequences of the US and Australian E. maxima isolates, respectively, and E. mitis Mit1 and Mit5 were designed to amplify the two different clones found in E. mitis isolate. M, Marker. C, D, E The drug resistance test results, including weight gain (C), lesion scores (D) and oocysts in one cecum per bird (E) were measured. Statistical analysis using ordinary one-way analysis of variance for weight gain (C) and t-tests for lesion scores (D) and oocysts in one cecum per bird (E). Asterisks indicate a significant difference at *P < 0.05, **P < 0.01, ***P < 0.001 and ****P < 0.0001; ns, not significant. F The resistance evaluation is based on three criteria: percentage of optimum anticoccidial activity (POAA; > 50% sensitivity, ≤ 50% resistance), reduction of lesion scores (RLS; > 50% sensitivity, ≤ 50% resistance) and relative oocyst production (ROP; ≥ 15% resistance, < 15% sensitivity). DecR, Decoquinate resistance; H, XJ, Houghton and Zinjiang original strains of E. tenella; INC, infected non-medicated controls; INC-P, parent strain non-medicated controls; NNC, non-infected, non-medicated birds; SC, decoquinate-resistant strain isolated from the field; SNP, single nucleotide polymorphism