Exogenous nitrous oxide (NO) stimulates egress of Eimeria tenella sporozoites. (A) NO concentrations released by different doses of sodium nitroferricyanide (II) dihydrate (SNP) for a variety of durations. (B) Primary chicken kidney cells (PCKs) were infected with sporozoites and incubated with different concentrations of SNP for different times. The number of free sporozoites was analyzed by flow cytometry. Data are means ± standard error of the mean (SEM) of four replicates, representing three independent experiments. **p < 0.01, comparing SNP with DMEM at the respective time point. (C) Video was captured from 20 to 25 min after SNP treatment; eight representative frames were selected and shown. Arrows indicate the egress process in two sporozoites. Bar: 20 μm.