Prevalence of Mycoplasma and Chlamydia in the nasal flora of dairy calves.

Nasal swabs from dairy calves in 20 selected herds were collected once in each of three sampling periods in one year and cultured for mycoplasmas and chlamydiae. Seventy-seven of 411 calves (19%) and 16 of 20 herds (80%) were positive for mycoplasmas at least once throughout the year, and all of 378 calves sampled from the 20 herds were negative for chlamydiae. Thirty-one percent of the isolates were Mycoplasma bovirhinis; other species isolated less frequently were Mycoplasma bovis, Mycoplasma arginini, and Acholeplasma laidlawaii. There was no evidence of respiratory tract disease at the time of sampling in calves studied.