This study was conducted to determine the optimal dose of the oral
solution of the ultrasonic extract of Radix dichroae (UERD) and to provide experimental support for a safe clinical dose for anticoccidial treatment of broiler chickens. Radix dichroae root extracts were prepared using the ultrasonic extraction method. The anticoccidial activity of the oral
solution prepared from the ultrasonic extract of Radix dichroae roots was tested in broiler chickens following oral
infection with a field isolate of E. tenella. Ninety Lingnan yellow broiler chickens (14 days old) were randomly divided into nine groups (n = 10), including six UERD oral
solution treatments (0.25, 0.50, 1.50, 2.50, 3.50, and 5.00%), a
toltrazuril group (0.10%), an E. tenella-infected control group, and a healthy control group. All groups were inoculated orally with 7 × 104 sporulated E. tenella oocysts (Guangdong strain) except for the healthy control group. The chickens in the seven drug-treated groups were administered a UERD oral
solution or
toltrazuril in
drinking water for 7 days. The anticoccidial efficacy of the UERD oral
solution was evaluated by the bloody diarrhoea severity level, relative
body weight gain (rBWG), lesion score, oocyst per gram (OPG), and anticoccidial index (ACI). Compared with the infected control group, there were no significant differences in the groups treated with UERD oral
solution or
toltrazuril with regard to the lesion changes in the caecal regions (P > 0.05); however, the blood contents, OPG, and oocyst score in three UERD oral
solution treatment groups (0.50, 1.50, and 2.50%) were significantly reduced, and the bloody diarrhoea was also alleviated. The ACI in three UERD oral
solution treatment groups (0.50%, ACI = 143.7; 1.50%, ACI = 151.0; and 2.50%, ACI = 144.3) was higher than that in the
toltrazuril group (ACI = 127.0), and the rBWG in the 1.50% UERD oral
solution treatment group (95.0%) was similar to that in the healthy control group (100%), which was also 12.5% higher than that in the
toltrazuril group (82.5%). The findings of this study demonstrated that the UERD oral
solution (0.50% ~ 2.50% dose range) showed better prevention, anticoccidial efficacy, and growth promotion effects than
toltrazuril (0.10%), and the 1.50% dose level of UERD oral
solution in water is the clinically recommended dose according to the present study conditions.