Metaphylactic effect of Diclazuril 0.25% in suckling beef calves, during a coccidiosis outbreak in extensive farming

The weight gain performance and oocysts reduction, as response to the metaphylactic treatment with Diclazuril 0.25% at the start of a coccidiosis outbreak, was studied by a cases-controls transverse study.Fifty-eight suckling calves of approximately 90 days old were randomly selected from an infected beef herd on extensive farming. The calves were weighted and individual faecal samples were taken for oocyst per gram count (OPG). Out of those, 29 were drenched with 1 mg kg−1 of Diclazuril in one oral dose (group T), since the other 29 remained as control group (group C). Samples for OPG and weights were measured again at days 7 and 21 after treatment, respectively. Later, the groups were divided (by the median) in higher or lower OPG counts, and were compared in the same way, in order to remove those without apparent infection (lower OPG counts).The faecal oocysts reduction reached 99.5% (p < 0.0001), for the treated group. Along the three weeks of study, an increment of 2.65 kg in 21 days (125 g day−1, p = 0.036), was seen in treated group respect to controls, but this difference increased to 3.94 kg in 21 days (p < 0.0001), when only the calves with higher OPG were taken into account.These results highlight the magnitude of the subclinical impact of coccidiosis, biased by the individual susceptibility to infection, which leads to get heavier infections and express higher oocysts output.