Efficacy of toltrazuril against artificial infections with Eimeria bovis in calves

Abstract

Eimeria bovis causes catarrhalic to haemorrhagic diarrhea, sometimes lethal, in calves. Two randomized blinded studies were conducted to examine the efficacy of toltrazuril (5 % oral suspension, single application) on experimental E. bovis infection. Sporulated oocysts of a pathogenic field strain were orally inoculated at a dose of 5×10⁴ (study 1) or 1×10⁵ (study 2) per calf (1-5 weeks old). Calves were allocated to groups of 8 to 9 animals as follows: A: sham treated control (both studies); study 1 (toltrazuril at 14 days post infection, dpi): B: 5 mg/kg body weight (bw), C: 15 mg/kg bw, D: 25 mg/kg bw; study 2 (15 mg toltrazuril/kg bw): E: treatment at 12 dpi, F: treatment at onset of clinical coccidiosis (18 dpi). General health, fecal consistency, oocyst excretion (opg) and body weight were assessed. In study 2, two to three calves each were necropsied for the pathomorphological examination of the intestines at dpi 16, 20, 28 (groups A and E) or at dpi 20, 28, 35 (group F). In study 1 onset of clinical coccidiosis was observed in the sham treated controls (A) at dpi 18 to 21 with mean oocyst counts of 4511 opg. Toltrazuril distinctly reduced the prevalence and severeness of diarrhea. Oocyst excretion was suppressed in most calves (14 out of 26) of groups B, C and D, the remaining calves excreting only few oocysts. Consequently, the mean opg were low with values of 106 (B), < 1 (C) and 2.5 (D). Early treatment (E) controlled the infection and prevented clinical disease while the effect of late treatment (F) was limited. The efficacy of toltrazuril was positively dose-correlated. The application of 15 mg toltrazuril/kg bw within the prepatent period recommended for the control of E. bovis infection.