A blinded, randomized, controlled, multi-centric field study was conducted on French dairy farms (n = 9) to evaluate the long term efficacy of metaphylactic, single oral treatments with either 1 mg/kg
body weight (BW) of
diclazuril (Vecoxan®), or 15 mg/kg BW of
toltrazuril (Baycox®) against natural
infections with Eimeria zuernii and/or Eimeria bovis, compared to untreated control animals. A total of 199 calves from nine commercial farms aged between 21 and 55 days old at the start of study were included and randomly allocated to one of three groups. Calves on all farms were observed for a period of 78 days post treatment, using both parasitological (oocyst excretion), and clinical parameters (faecal score and
body weight). The assessment of efficacy was based on both control of oocyst excretion, and on the average daily
weight gains throughout the study. During the whole study period, the mean number of days with diarrhoea (≥ 2) was similar (0.7 days) between treated groups. Excretion in the untreated group peaked at 21 days
after treatment. In both the
diclazuril and
toltrazuril-treated groups, mean oocyst excretion decreased dramatically in the five days following treatment. Thereafter, particularly towards the end of the study period, oocyst counts and percentage levels of E. zuernii were highest in the
toltrazuril-treated group. In pooled data from all trial sites, the average daily
weight gain was significantly (p = 0.01) higher (+ 0.057 kg/day) in the
diclazuril group when compared to the
toltrazuril group, and the average
body weight gain of the
diclazuril treated group was 4.4 kg higher than the
toltrazuril group. On eight of the nine trial sites, the average daily gain was greater in the
diclazuril group than in the
toltrazuril group. This study demonstrates that, over an extended observation period of 78 days, metaphylactic treatment with both
diclazuril and
toltrazuril reduces the impact of
coccidiosis, but greater performance benefits based on average daily
weight gains, were achieved following the use of
diclazuril.