G. Zechner and colleagues write: We are grateful for the opportunity to reply to the letter from Bhushan and others (2016) regarding our paper ‘Efficacy of diclazuril and toltrazuril in the prevention of coccidiosis in dairy cows under field conditions’ (Zechner and others 2015). The full online version of this paper was subject to peer review, and the study was conducted to full Good Clinical Practice Standards and in accordance with national animal ethics legislation and approval. To address the more specific points raised, we are able to provide the following further points of clarification. In the online paper, treatment protocols are clearly indicated with the date of treatment predetermined based on anticipated periods of risk, which for each animal followed the movement from single pens to the barns, and before clinical outbreaks of disease were expected or predicted. Under commercial farm conditions, the actual date of treatment would be determined by the individual calves' birth dates and so would have occurred on different dates, but each calf was designated day 0 in the study. All treatments were blinded …