Allen, J. W., K. G. Bateman, L. Viel, S. Rosendal, and P. E. Shewen. “The Microbial Flora of the Upper and Lower Respiratory Tracts of Feedlot Calves With Undifferentiated Bovine Respiratory Disease”. The Bovine Practitioner, vol. 1991, no. 26, Sept. 1991, pp. 162-5, doi:10.21423/bovine-vol1991no26p162-165.