Antimicrobial resistance in livestock is a growing concern due to possible transmission to humans. Thus, it is important to understand antimicrobial use in farm animals. Dairy calves receive antimicrobials for the treatment of respiratory diseases, but it is unclear under what circumstances antimicrobials are used. The objective of this study is to investigate antimicrobial use and case-specific information used in treating respiratory diseases in Canadian dairy calves. A total of 105 dairy farmers (Ontario: 31; Alberta: 28; British Columbia: 26; Nova Scotia: 20) were selected purposively and completed a questionnaire in person about calf health. First, farmers were asked, “Do you use antimicrobials to treat respiratory diseases in calves”?. Second, only those who used antimicrobials to treat respiratory diseases were asked, “What case-specific information do you use to select a respiratory disease case for antimicrobial treatment”?. Respondents were instructed to select all that apply from a list of 4 symptoms (elevated breathing/respiratory rate, spontaneous/induced coughing, fever, presence of nasal/eye discharge) or otherwise specified. The average herd size was 162 milking cows (range 36–560). Among 105 farmers, 98% used antimicrobials to treat respiratory diseases. Among those who used antimicrobials for respiratory diseases, 80% used “elevated breathing/respiratory rate,” 67% used “spontaneous/induced coughing,” 61% used “fever,” 48% used “presence of nasal/eye discharge,” and 33% used other characteristics as indicators to treat respiratory diseases with antimicrobials. Among 34 farmers who specified other characteristics than symptoms given, 38% used “lethargy” and 35% used “lack of appetite” as an indicator for treatment. Among 91 farmers who were asked whether they had a written treatment protocol for respiratory diseases in calves, 35% reported that they have the protocol and 97% of them were discussed with veterinarians. Treatment decisions could be refined with inclusion of additional simple criteria to identify calves that require antimicrobials for their health or welfare.